Feedback | Help | Exit
Journal of Applied Physics
Search:
   
 
 
 

BROWSE VOLUME

Year Range:  

15 May 2009

Volume 105, Issue 10,  Articles (10xxxx)

back to top

SPECIAL TOPIC: APPLIED BIOPHYSICS

Preface to Special Topic: Applied Biophysics

Andreas Mandelis, Gerald J. Diebold, Takehiko Kitamori, Akihide Hibara, and I. Alex Vitkin

J. Appl. Phys. 105, 101901 (2009) (2 pages)

Online Publication Date: 19 May 2009

Full Text: HTML | Sectioned HTML | PDF (47 kB)

+
 Abstract Unavailable
Show PACS
01.30.-y, 87.63.D-, 87.63.L-, 87.80.Ek, 87.61.-c, 87.59.B-

X-ray elastography: Modification of x-ray phase contrast images using ultrasonic radiation pressure

Theron J. Hamilton, Claude Bailat, Stephan Gehring, Christopher M. Laperle, Jack Wands, Christoph Rose-Petruck, and Gerald J. Diebold

J. Appl. Phys. 105, 102001 (2009) (4 pages)

Online Publication Date: 19 May 2009

Full Text: HTML | Sectioned HTML | PDF (360 kB)

Show Abstract
The high resolution characteristic of in-line x-ray phase contrast imaging can be used in conjunction with directed ultrasound to detect small displacements in soft tissue generated by differential acoustic radiation pressure. The imaging method is based on subtraction of two x-ray images, the first image taken with, and the second taken without the presence of ultrasound. The subtraction enhances phase contrast features and, to a large extent, removes absorption contrast so that differential movement of tissues with different acoustic impedances or relative ultrasonic absorption is highlighted in the image. Interfacial features of objects with differing densities are delineated in the image as a result of both the displacement introduced by the ultrasound and the inherent sensitivity of x-ray phase contrast imaging to density variations. Experiments with ex vivo murine tumors and human tumor phantoms point out a diagnostic capability of the method for identifying tumors.
Show PACS
87.59.B-, 87.63.D-, 43.80.Qf, 87.19.R-, 87.19.xj

X-ray phase contrast imaging: Transmission functions separable in cylindrical coordinates

Guohua Cao, Theron Hamilton, Christopher M. Laperle, Christoph Rose-Petruck, and Gerald J. Diebold

J. Appl. Phys. 105, 102002 (2009) (6 pages)

Online Publication Date: 19 May 2009

Full Text: HTML | Sectioned HTML | PDF (395 kB)

Show Abstract
A Fresnel–Kirchhoff integral can be used to calculate x-ray phase contrast images when the transmission function is known. Here expressions for image intensity are derived for objects with axial symmetry for an x-ray source with non-vanishing dimensions. An expression for the image intensity is given for an x-ray source whose intensity distribution is described by a Gaussian function, from which an expression for the limiting case of a point source of radiation is found. The expressions for image intensity are evaluated for cases where the magnification is substantially greater than one, as would be employed in biological imaging. Experiments using a microfocus x-ray tube and charge coupled device camera are reported to determine the capability of the method for imaging small spherical objects, such as gold particles, which might find application as contrast agents in biomedical imaging.
Show PACS
87.59.B-, 07.85.Fv

Mechanism of voltage production and frequency dependence of the ultrasonic vibration potential

Cuong K. Nguyen, Shougang Wang, and Gerald Diebold

J. Appl. Phys. 105, 102003 (2009) (4 pages)

Online Publication Date: 19 May 2009

Full Text: HTML | Sectioned HTML | PDF (187 kB)

Show Abstract
Imaging with the ultrasonic vibration potential is based on voltage generation by a colloidal or ionic suspension in response to the passage of ultrasound. The polarization within a body arising from the oscillatory displacement in the ultrasonic field produces a current in a pair of external electrodes that is measured as a function of time or frequency. Existing theory gives the current in the electrodes as arising from both a time varying polarization and ionic conduction. Here, experiments are reported that show the production of the polarization current is the dominant mechanism for current generation in soft tissue. Experiments are also reported giving the frequency dependence of the ultrasonic vibration current in canine blood and in several dilutions of aqueous silica suspensions.
Show PACS
87.50.yg, 43.35.Wa, 43.35.Bf, 43.40.Ng

Hyperpolarized noble gas magnetic resonance imaging of the animal lung: Approaches and applications

Giles E. Santyr, Wilfred W. Lam, Juan M. Parra-Robles, Timothy M. Taves, and Alexei V. Ouriadov

J. Appl. Phys. 105, 102004 (2009) (13 pages)

Online Publication Date: 19 May 2009

Full Text: HTML | Sectioned HTML | PDF (1288 kB)

Show Abstract
Hyperpolarized noble gas (HNG) magnetic resonance (MR) imaging is a very promising noninvasive tool for the investigation of animal models of lung disease, particularly to follow longitudinal changes in lung function and anatomy without the accumulated radiation dose associated with x rays. The two most common noble gases for this purpose are 3He (helium 3) and 129Xe (xenon 129), the latter providing a cost-effective approach for clinical applications. Hyperpolarization is typically achieved using spin-exchange optical pumping techniques resulting in ~10 000-fold improvement in available magnetization compared to conventional Boltzmann polarizations. This substantial increase in polarization allows high spatial resolution (<1  mm) single-slice images of the lung to be obtained with excellent temporal resolution (<1  s). Complete three-dimensional images of the lungs with 1 mm slice thickness can be obtained within reasonable breath-hold intervals (<20  s). This article provides an overview of the current methods used in HNG MR imaging with an emphasis on ventilation studies in animals. Special MR hardware and software considerations are described in order to use the strong but nonrecoverable magnetization as efficiently as possible and avoid depolarization primarily by molecular oxygen. Several applications of HNG MR imaging are presented, including measurement of gross lung anatomy (e.g., airway diameters), microscopic anatomy (e.g., apparent diffusion coefficient), and a variety of functional parameters including dynamic ventilation, alveolar oxygen partial pressure, and xenon diffusing capacity.
Show PACS
87.61.-c, 87.19.X-

Refracting Röntgen's rays: Propagation-based x-ray phase contrast for biomedical imaging

T. E. Gureyev, S. C. Mayo, D. E. Myers, Ya. Nesterets, D. M. Paganin, A. Pogany, A. W. Stevenson, and S. W. Wilkins

J. Appl. Phys. 105, 102005 (2009) (12 pages)

Online Publication Date: 19 May 2009

Full Text: HTML | Sectioned HTML | PDF (752 kB)

Show Abstract
Absorption-contrast x-ray imaging serves to visualize the variation in x-ray attenuation within the volume of a given sample, whereas phase contrast allows one to visualize variations in x-ray refractive index. The former imaging mechanism has been well known and widely utilized since the time of Röntgen's Nobel prize winning work, whereas the latter mechanism—sought for, but not found, by Röntgen himself—has laid the foundation for a revolution in x-ray imaging which is the central topic of this review. We consider the physical imaging mechanisms underlying both absorption contrast and phase contrast, together with the associated inverse problem of how one may obtain quantitative two- or three-dimensional information regarding a sample, given one or more phase-contrast images of the same. Practical questions are considered, regarding optimized phase-contrast imaging geometries as a function of detector resolution, source size, x-ray spectrum, and dose. Experimental examples pertaining to biomedical applications are given, and prospects for the future outlined.
Show PACS
87.59.B-, 87.57.cf, 87.64.kd

X-ray dark-field and phase-contrast imaging using a grating interferometer

F. Pfeiffer, M. Bech, O. Bunk, T. Donath, B. Henrich, P. Kraft, and C. David

J. Appl. Phys. 105, 102006 (2009) (4 pages)

Online Publication Date: 19 May 2009

Full Text: HTML | Sectioned HTML | PDF (752 kB)

Show Abstract
In this letter, we report results obtained with a recently developed approach for grating-based x-ray dark-field imaging [F. Pfeiffer et al., Nat. Mater. 7, 134 (2008)]. Since the image contrast is formed through the mechanism of small-angle scattering, it provides complementary and otherwise inaccessible structural information about the specimen at the micron and submicron length scales. Our approach is fully compatible with conventional transmission radiography and the grating-based hard x-ray phase-contrast imaging scheme [F. Pfeiffer et al., Nat. Phys. 2, 258 (2006)]. Since it can be used with standard x-ray tube sources, we envisage widespread applications to x-ray medical imaging, industrial nondestructive testing, or security screening.
Show PACS
07.85.-m, 42.79.Dj, 07.60.Ly

Alkene epoxidation with a polystyrene immobilised metal salen catalyst in a continuous-flow microfluidic reactor

Christopher J. Cullen, Robert C. R. Wootton, and Andrew J. de Mello

J. Appl. Phys. 105, 102007 (2009) (4 pages)

Online Publication Date: 19 May 2009

Full Text: HTML | Sectioned HTML | PDF (281 kB)

Show Abstract
The epoxidation of styrene using a modularly constructed polymer immobilized Mn(III)-salen catalyst has been demonstrated within a continuous-flow glass fabricated microfluidic reactor.
Show PACS
82.35.-x, 47.85.Np, 82.30.Vy

Real-time fast inverse dose optimization for image guided adaptive radiation therapy–Enhancements to fast inverse dose optimization (FIDO)

S. P. Goldman, D. Turnbull, C. Johnson, J. Z. Chen, and J. J. Battista

J. Appl. Phys. 105, 102008 (2009) (11 pages)

Online Publication Date: 19 May 2009

Full Text: HTML | Sectioned HTML | PDF (2748 kB)

Show Abstract
A fast, accurate and stable optimization algorithm is very important for inverse planning of intensity-modulated radiation therapy (IMRT), and for implementing dose-adaptive radiotherapy in the future. Conventional numerical search algorithms with positive beam weight constraints generally require numerous iterations and may produce suboptimal dose results due to trapping in local minima regions of the objective function landscape. A direct solution of the inverse problem using conventional quadratic objective functions without positive beam constraints is more efficient but it will result in unrealistic negative beam weights. We review here a direct solution of the inverse problem that is efficient and does not yield unphysical negative beam weights. In fast inverse dose optimization (FIDO) method the objective function for the optimization of a large number of beamlets is reformulated such that the optimization problem is reducible to a linear set of equations. The optimal set of intensities is then found through a matrix inversion, and negative beamlet intensities are avoided without the need for externally imposed ad hoc conditions. In its original version [S. P. Goldman, J. Z. Chen, and J. J. Battista, in Proceedings of the XIVth International Conference on the Use of Computers in Radiation Therapy, 2004, pp. 112–115; S. P. Goldman, J. Z. Chen, and J. J. Battista, Med. Phys. 32, 3007 (2005)], FIDO was tested on single two-dimensional computed tomography (CT) slices with sharp KERMA beams without scatter, in order to establish a proof of concept which demonstrated that FIDO could be a viable method for the optimization of cancer treatment plans. In this paper we introduce the latest advancements in FIDO that now include not only its application to three-dimensional volumes irradiated by beams with full scatter but include as well a complete implementation of clinical dose-volume constraints including maximum and minimum dose as well as equivalent uniform dose constraints. The method has been integrated into a commercial treatment planning system (Pinnacle, Philips Medical Systems) for beta testing using clinical radiotherapy cases and standard dose constraints set by radiation oncologists. Our FIDO method consistently delivered excellent treatment plans comparable and often better than those obtained using standard optimization techniques that are considerably slower. By design, FIDO is guaranteed to find a global minimum and will achieve highly conformal and homogeneous dose distributions without the need for artificial internal contours that must be created in conventional IMRT optimization systems to help the search engines better control some beam entry directions and in this way avoid the creation of hot and cold spots. This method provides a fast, intuitive and robust technique that yields excellent results for the inverse planning of IMRT. FIDO's ability to efficiently optimize very large numbers of beamlet weights also makes it an ideal tool for the optimization of helical tomotherapy. Future gains in speed will make it possible to use FIDO for instant treatment plan reoptimization using CT images produced at the radiotherapy machine, just prior to daily treatments of the patient.
Show PACS
87.53.Jw, 87.53.Bn, 87.55.de, 87.55.dk, 02.30.Zz, 87.57.Q-, 87.19.xj

The past, present, and future of x-ray technology for in vivo imaging of function and form

A. Fouras, M. J. Kitchen, S. Dubsky, R. A. Lewis, S. B. Hooper, and K. Hourigan

J. Appl. Phys. 105, 102009 (2009) (14 pages)

Online Publication Date: 19 May 2009

Full Text: HTML | Sectioned HTML | PDF (3944 kB)

Show Abstract
Scientists and clinicians have a keen interest in studying not just the structure of physiological systems, but their motion also, or more generally their form and function. This paper focuses on the technologies that underpin in vivo measurements of form and function of the human body for both research and medical treatment. A concise literature review of x-ray imaging, ultrasonography, magnetic resonance imaging, radionuclide imaging, laser Doppler velocimetry, and particle image velocimetry is presented. Additionally, a more detailed review of in vivo x-ray imaging is presented. Finally, two techniques, which the authors believe are representative of the present and future of in vivo x-ray imaging techniques, are presented.
Show PACS
87.59.B-

Multimodal optical imaging and spectroscopy for the intraoperative mapping of nonmelanoma skin cancer

Elena Salomatina, Alona Muzikansky, Victor Neel, and Anna N. Yaroslavsky

J. Appl. Phys. 105, 102010 (2009) (7 pages)

Online Publication Date: 19 May 2009

Full Text: HTML | Sectioned HTML | PDF (852 kB)

Show Abstract
Basal cell carcinoma (BCC) is the most common human malignancy, and its incidence increases yearly. In this contribution we investigate the feasibility of combining multimodal reflectance and fluorescence polarization imaging (RFPI) with spectroscopic analysis of the reflectance images for facilitating intraoperative delineation of BCCs. Twenty fresh thick BCC specimens were obtained within 1 h after Mohs micrographic surgeries. The samples were soaked for up to 2 min in an aqueous 0.2 mg/ml solution of methylene blue, briefly rinsed in saline solution, and imaged. Reflectance images were acquired in the range from 395 to 735 nm, with steps of 10 nm. Fluorescence polarization images were excited at 630 nm and registered in the range between 660 and 750 nm. The results yielded by RFPI were qualitatively compared to each other and to histopathology. From the copolarized reflectance images the spectral responses including the optical densities and their wavelength derivatives were calculated. The differences in the spectral responses of the benign and malignant stained skin structures were assessed. Statistical analysis, i.e., Student's t-test, was employed to verify the significance of the discovered differences. Both reflectance and fluorescence polarization images correlated well with histopathology in all the cases. Reflectance polarization images provided more detailed information on skin morphology, with the appearance of skin structures resembling that of histopathology. Fluorescence polarization images exhibited higher contrast of cancerous tissue as compared to reflectance imaging. The analysis of the optical densities and their wavelength derivatives for tumor and normal tissues has confirmed statistical significance of the differences that can be used for intraoperative cancer delineation. The results of the study indicate that spectral analysis is a useful adjunct to RFPI for facilitating skin cancer delineation.
Show PACS
87.63.L-, 87.64.kv, 87.17.-d, 02.50.-r, 87.57.nj, 87.19.xj

Electron and photon spread contributions to the radiological penumbra for small monoenergetic x-ray beam (<=2  MeV)

Jean-Philippe Pignol and Brian M. Keller

J. Appl. Phys. 105, 102011 (2009) (5 pages)

Online Publication Date: 19 May 2009

Full Text: HTML | Sectioned HTML | PDF (1188 kB)

Show Abstract
Our team has previously published that submegavoltage photons could significantly improve the radiological penumbra for small size radiation fields. The present work uses Monte Carlo simulation to evaluate the contributions of secondary electrons and photon scatter to the penumbra region for various field sizes (5, 10, 20, and 40 mm in diameters) and for various monoenergetic photon beams (200, 400, 600, 800, 1000, and 2000 keV, and a standard 6 MV beam), minimizing geometrical and transmission penumbra. For field sizes less than 2 cm in diameter, photon scatter is negligible such that the secondary electrons are the main contributor to the radiological penumbra. Reducing the photon beam energy to the submegavoltage range reduces the range of secondary electrons and eventually improves the beam boundary sharpness. Provided that the geometrical penumbra and patient immobilization system are optimized, submegavoltage photon beams with effective photon energies in the 300 to 600 keV range, present significant advantages for multiple beam stereotactic irradiations of tumors less than 2 cm in diameter.
Show PACS
87.53.Ly, 87.53.Jw, 87.55.kh, 87.19.xj

Thrombin generation test in microfluidic systems

Kaspar Koch, Sander S. van Berkel, Marloes M. E. B. van de Wal, Pieter J. Nieuwland, Jan C. M. van Hest, and Floris P. J. T. Rutjes

J. Appl. Phys. 105, 102012 (2009) (5 pages)

Online Publication Date: 19 May 2009

Full Text: HTML | Sectioned HTML | PDF (505 kB)

Show Abstract
The thrombin generation test is one of the diagnostic tests currently in use as a universal method for measuring hemostatic disorders. We envisioned that conventional monitoring of thrombin generation could be miniaturized resulting in a time-saving, accurate, easy-to-operate, and cost-efficient test. For the translation of the conventional thrombin generation test to microfluidic devices, our focus was directed to parameters such as the detection limit, temperature, protein-surface interactions (i.e., hydrophilicity of microchannels), and mixing behavior. Scaling down to microchannels (e.g., capillaries) resulted in volume reduction and allowed us to study the effect of a microchannel surface (either hydrophilic or hydrophobic) on the thrombin activity. Finally, the use of a micromixer enabled us to perform efficient on-chip mixing, resulting in the successful measurement of a thrombin generation in a microfluidic device.
Show PACS
87.85.Ox, 85.85.+j, 47.85.Np, 87.14.ej, 87.19.U-, 87.15.K-

Towards microsystems for automatic acquisition of in vivo gastrointestinal information

Katsuya Morimoto, Shigeki Yamaguchi, Junji Fukuda, and Hiroaki Suzuki

J. Appl. Phys. 105, 102013 (2009) (7 pages)

Online Publication Date: 19 May 2009

Full Text: HTML | Sectioned HTML | PDF (305 kB)

Show Abstract
The possibility to develop a microanalysis system for the acquisition of gastrointestinal information is presented here. The system consists of four assay sites for trypsin, pepsin, and other biochemical compounds. The major components in each assay site were a pH-responsive valve, a pH-stat used to maintain the pH of the solution to be analyzed and used for electrochemical pH-titration, and a freeze-dried enzyme substrate stored in the pH-stat. The operation of the valve is based on electrowetting, and the valve is made pH-responsive by means of a nonstandard three-electrode system. The sample solution was automatically injected into the compartment and rapidly dissolved into the substrate layer. The automatic pH-stat, based on another nonstandard use of the electrochemical three-electrode system, maintained the solution pH and, at the same time, conducted pH-titration. The determination of the activity of the proteases was conducted at their optimum pHs. The output current showed a clear dependence on the activity of the enzymes. Integrating the functions provides significant advantages for the use of this system as an isolated telemetric microsystem that may operate with wireless signal transmission using a small power supply.
Show PACS
87.85.Ox, 85.85.+j, 87.19.xu, 87.14.ej, 82.45.Fk, 87.15.N-

Cell manipulation with magnetic particles toward microfluidic cytometry

Chengxun Liu, Tim Stakenborg, Sara Peeters, and Liesbet Lagae

J. Appl. Phys. 105, 102014 (2009) (11 pages)

Online Publication Date: 19 May 2009

Full Text: HTML | Sectioned HTML | PDF (5515 kB)

Show Abstract
Magnetic particles have become a promising tool for nearly all major lab-on-a-chip (LOC) applications, from sample capturing, purification, enrichment, transport to detection. For biological applications, the use of magnetic particles is especially well established for immunomagnetic separation. There is a great amount of interest in the automation of cell sorting and counting with magnetic particles in LOC platforms. So far, despite great efforts, only few fully functional LOC devices have been described and further integration is necessary. In this review, we will describe the physics of magnetic cell sorting and counting in LOC formats with a special focus on recent progress in the field.
Show PACS
87.80.Ek, 85.85.+j, 87.17.-d, 87.80.Fe, 47.85.Np

Quantification of Ag(I) and kinetic analysis using ion-pair extraction across a liquid/liquid interface in a laminar flow by fluorescence microscopy

Hidenori Nagai, Natsuko Miwa, Miho Segawa, Shin-ichi Wakida, and Kenji Chayama

J. Appl. Phys. 105, 102015 (2009) (7 pages)

Online Publication Date: 19 May 2009

Full Text: HTML | Sectioned HTML | PDF (752 kB)

Show Abstract
To analyze the kinetics of complicate ion-pair extraction, we have utilized a microfluidic approach and fluorescence detection. We have already developed a Ag(I)-specific thia-crown ether as an ion-association reagent. Furthermore, a fluorescent anion was added to detect the generated complex of Ag(I), ion-association reagent, and the counteranion in the ion-pair extraction system. A two-phase laminar flow consisting of an aqueous liquid and an organic liquid in a microchannel was formed, and the relationship between the initial conditions and reaction rate was examined. The microfluidic device could realize a spatiotemporal approach to solvent extraction, because the traveling length along the interface corresponded to the reaction time. The rate-determining step was estimated according to ion-pair formation behavior. Furthermore, due to the miniaturized reaction volume in the microchannel, rapid extraction of Ag(I) was achieved. The microchannel width was optimized to carry out the rapid extraction of Ag(I). In the application of the microfluidic device, the quantification of Ag(I) was examined and exhibited good linearity in the range of 6.1×10−7–4×10−6M. The lower limit of detection was almost the same as for an atomic absorption spectrometer.
Show PACS
82.30.Nr, 82.20.-w, 47.85.Np, 47.61.Jd, 47.15.Rq, 85.85.+j

Single-biomolecule observation with micro one-way valves for rapid buffer exchange

Yoko Hirono-Hara, Hiroyuki Noji, and Shoji Takeuchi

J. Appl. Phys. 105, 102016 (2009) (5 pages)

Online Publication Date: 19 May 2009

Full Text: HTML | Sectioned HTML | PDF (1515 kB)

Show Abstract
This paper describes a method for the rapid exchange of buffer solution during single-molecule observation. We use a simple, transparent, all-plastic one-way valve integrated on a coverslip on a flow cell. The valve is formed using a membrane made of parylene covering a microhole. It opens when a buffer solution is introduced from the microhole (the flow pushes the cover membrane) and closes when suctioning the buffer solution (the membrane is pulled back and seals the microhole to prevent the diffusion of the solution). To check valve performance, we observed the response of a rotary biomotor, F1-ATPase, for several buffer solutions in the fabricated chamber.
Show PACS
87.80.Ek, 87.16.dp, 87.15.Vv, 87.15.N-, 85.85.+j, 47.63.-b

Quantification of disease marker in undiluted serum using an actuating layer-embedded microcantilever

Kyo Seon Hwang, Hye Kyung Jeon, Sang-Myung Lee, Sang Kyung Kim, and Tae Song Kim

J. Appl. Phys. 105, 102017 (2009) (7 pages)

Online Publication Date: 19 May 2009

Full Text: HTML | Sectioned HTML | PDF (817 kB)

Show Abstract
In this study, we describe the application feasibility of a dynamic microcantilever with regard to the detection of a specific protein in human serum or real blood using an end-point analysis. The mechanical response (i.e., resonant frequency) of a functionalized dynamic microcantilever was shown to be altered by molecular interactions, which allowed for the detection of biomolecules present in small quantities without any additional signal enhancements, such as labeling. For the application of the microcantilever sensors to bioassays of serum samples, the mechanical response from the nonspecific adsorption of abundant proteins must be reduced, because it significantly influences the output signal deviation of the microcantilever sensor. We implemented a label-free prostate specific antigen (PSA) detection protocol in standard serum via our established process, which was designed to minimize nonspecific protein adsorption. PSA is a tumor marker for prostate cancer, with a threshold concentration of 2–4 ng/ml (7.2–14.4 pM) for the distinction between patients and normal individuals. The dynamic range of our dynamic microcantilever-based PSA assay on the background of standard serum ranged between 0.1 and 100 ng/ml (3.6 and 3600 pM). It was suggested that the dynamic microcantilever might allow for the sensitive label-free detection of disease markers in an actual human sample.
Show PACS
87.85.Ox, 85.85.+j, 87.19.xj, 87.14.E-, 87.15.K-, 87.80.Ek

Hadamard transform microchip electrophoresis combined with laser-induced fluorescence detection using a compact neodymium-doped yttrium aluminum garnet laser emitting at 532 nm

Kazuki Hata, Takashi Kaneta, and Totaro Imasaka

J. Appl. Phys. 105, 102018 (2009) (6 pages)

Online Publication Date: 19 May 2009

Full Text: HTML | Sectioned HTML | PDF (393 kB)

Show Abstract
Hadamard transform electrophoresis combined with laser-induced fluorescence (LIF) detection on a microchip was demonstrated. A compact, diode-pumped neodymium-doped yttrium aluminum garnet laser was employed as the light source for LIF detection. The analytical conditions were optimized using rhodamine B as the analyte. Under optimal conditions, the signal-to-noise ratio (S/N) of the analyte was improved by a factor of 7.5 by means of Hadamard transformation based on a 255-order cyclic S matrix. Additionally, the relationship between fluorescence intensity and analyte concentration was linear with a correlation coefficient of 0.993 in the inverse Hadamard transformed data at the concentration range from 25 to 100 pM. The results indicate that the present method is applicable to quantitative analysis at the concentration lower than the concentration limit of detection in a conventional method. The concentration limit of detection was ~25  pM (the relative standard deviation of the peak height was 5.2%). The present technique was successfully applied to the separation of a mixture containing 1.9 nM phenylalanine and 1.9 nM glutamic acid labeled with rhodamine B isothiocyanate. The S/Ns of the analyte peaks were improved up to ~10 in the inverse Hadamard transformed data derived from a 127-order cyclic S matrix, while neither peak was lower than the limit of detection (S/N<3) in conventional microchip electrophoresis by a single injection.
Show PACS
87.80.Ek, 42.62.Be, 87.15.Tt, 02.30.Uu, 87.64.kv, 87.15.N-

An easy cell-based microchip assay method for a CYP1A1-mediated drug metabolism using adhesive cells, HepG2

Masaru Kato, Tatsuhiro Yamamoto, Masashi Sekimoto, Masakuni Degawa, and Toshimasa Toyo'oka

J. Appl. Phys. 105, 102019 (2009) (4 pages)

Online Publication Date: 19 May 2009

Full Text: HTML | Sectioned HTML | PDF (203 kB)

Show Abstract
We have developed a convenient cell-based assay method using a microchip. In the method, adhesive cells, HepG2, were cultured in the conventional culture dish containing glass disks and then the disks covered with the HepG2 were transferred to the microchip for cell assay. Activity of ethoxyresorufin O-deethylation (EROD), which is mainly mediated by cytochrome P4501A1 (CYP1A1), in HepG2 was measured. Treatment of HepG2 with 3-methylcholanthrene, a CYP1A1 inducer, resulted in significant increase in EROD activity.
Show PACS
87.80.-y, 87.15.R-, 87.18.-h

Signal-to-noise ratio improvement of peptide microarrays by using hyperbranched-polymer materials

Takeshi Mori, Go Yamanouchi, Xiaoming Han, Yusuke Inoue, Syuhei Shigaki, Takayuki Yamaji, Tatsuhiko Sonoda, Kei Yasui, Hisato Hayashi, Takuro Niidome, and Yoshiki Katayama

J. Appl. Phys. 105, 102020 (2009) (6 pages)

Online Publication Date: 19 May 2009

Full Text: HTML | Sectioned HTML | PDF (366 kB)

Show Abstract
The fabrication of peptide microarrays using hyperbranched polymers (HBPs) to improve the signal-to-noise ratio was demonstrated. Due to a high density of reactive groups at the chain ends of the HBPs, as well as to their spherical shape, HBPs can be used as linkers to increase the amount of immobilized peptides through raising the specific surface area of the glass substrate. A zwitterionic HBP was used as a blocking agent to reduce the noise level of the peptide microarrays. The zwitterionic HBP shows comparably excellent blocking ability to a commercially available BSA-based blocking agent. Thus, it was concluded that HBPs have high potential for the fabrication of highly sensitive peptide microarrays.
Show PACS
87.15.rp, 82.35.-x, 36.20.-r, 82.35.Pq

On scaling laws of biosensors: A stochastic approach

Shreepriya Das, Haris Vikalo, and Arjang Hassibi

J. Appl. Phys. 105, 102021 (2009) (7 pages)

Online Publication Date: 19 May 2009

Full Text: HTML | Sectioned HTML | PDF (665 kB)

Show Abstract
We study the scaling laws of affinity-based biosensors. In particular, we examine the implications of scaling on the response time, signal-to-noise ratio (SNR), and dynamic range (DR) of biosensor systems. Initially, using stochastic differential methods and particularly Fokker–Planck (FP) equation, we formulate the analyte capturing process and derive its uncertainty by computing the probability distribution function of the captured analytes as a function of time. Subsequently, we examine the effects of scaling on the solution to the FP equation and the signal fluctuation, which demonstrates that scaling down significantly reduces the achievable SNR and DR of biosensors. We argue that these results question the advantages of excessive miniaturization of biosensors, especially the fundamental SNR limitation, which transpire in the micro- and nanoregimes.
Show PACS
87.80.Ek, 87.10.Mn, 85.85.+j, 07.07.Df, 07.10.Cm

Theoretical analysis of coupled diffuse-photon-density and thermal-wave field depth profiles photothermally generated in layered turbid dental structures

Anna Matvienko, Andreas Mandelis, Raymond J. Jeon, and Stephen H. Abrams

J. Appl. Phys. 105, 102022 (2009) (15 pages)

Online Publication Date: 19 May 2009

Full Text: HTML | Sectioned HTML | PDF (433 kB)

Show Abstract
A coupled diffuse-photon-density and thermal-wave model is developed for theoretical analysis of the photothermal field in demineralized teeth. Intact and demineralized layers of enamel, as well as dentin, are described as a layered one-dimensional system. The solution of the radiative transport equation in the limit of diffuse-photon-density field is considered as a source term in the thermal-wave field equation. The influence of optical parameters (absorption and scattering coefficients) and thermal parameters (thermal diffusivity and conductivity) of each layer on the diffuse-photon-density and thermal-wave depth profiles is analyzed using computer simulations, allowing the verification of accuracy and validity of the developed theory. The proposed model and simulations are intended for identifying the parameters most affecting the diffuse-photon-density and thermal-wave fields in turbid media, which leads to optimization of the fitting process of thermal and optical properties of teeth from experimental data obtained by frequency-domain photothermal radiometry.
Show PACS
87.85.jc, 87.19.Pp, 87.10.-e

Polarimetry in turbid, birefringent, optically active media: A Monte Carlo study of Mueller matrix decomposition in the backscattering geometry

Nirmalya Ghosh, Michael F. G. Wood, and I. Alex Vitkin

J. Appl. Phys. 105, 102023 (2009) (8 pages)

Online Publication Date: 19 May 2009

Full Text: HTML | Sectioned HTML | PDF (266 kB)

Show Abstract
Determination of the intrinsic polarization properties of a complex turbid medium such as biological tissue in the backscattering geometry (a geometry that is convenient for in situ applications) is complicated due to the confounding influence of scattering, and due to simultaneous occurrence of several polarization effects. We have investigated the polar decomposition approach of Mueller matrices to delineate individual intrinsic polarization parameters (specifically linear retardance delta and optical rotation psi) of a birefringent, chiral, turbid medium in the backscattering geometry, using Mueller matrices generated with polarization-sensitive Monte Carlo simulations. The results show that near the exact backscattering direction, the interplay of the scattering-induced linear retardance and diattenuation on the intrinsic values for delta and psi is coupled in a complex interrelated way, due to contribution of the backscattered photons. In contrast, these effects were significantly reduced for detection positions at distances larger than a transport length away from the point of illumination. Simultaneous determination of the intrinsic values for delta and psi of a birefringent, chiral, turbid medium in the backward detection geometry can thus be accomplished by decomposing the Mueller matrices recorded at distances larger than a transport length away from the point of illumination. Determination of the intrinsic values for these polarization parameters in backscattering geometry could be significant in, for example, for quantification of tissue structural anisotropy and for noninvasive blood glucose measurements of diabetic patients.
Show PACS
87.64.Cc, 87.50.wf, 87.10.Rt, 02.10.Yn

Spectral distortion in diffuse molecular luminescence tomography in turbid media

Scott C. Davis, Brian W. Pogue, Stephen B. Tuttle, Hamid Dehghani, and Keith D. Paulsen

J. Appl. Phys. 105, 102024 (2009) (8 pages)

Online Publication Date: 19 May 2009

Full Text: HTML | Sectioned HTML | PDF (801 kB)

Show Abstract
The influence of tissue optical properties on the shape of near-infrared (NIR) fluorescence emission spectra propagating through multiple centimeters of tissue-like media was investigated. Fluorescence emission spectra measured from 6 cm homogeneous tissue-simulating phantoms show dramatic spectral distortion which results in emission peak shifts of up to 60 nm in wavelength. Measured spectral shapes are highly dependent on the photon path length and the scattered photon field in the NIR amplifies the wavelength-dependent absorption of the fluorescence spectra. Simulations of the peak propagation using diffusion modeling describe the experimental observations and confirm the path length dependence of fluorescence emission spectra. Spectral changes are largest for long path length measurements and thus will be most important in human tomography studies in the NIR. Spectrally resolved detection strategies are required to detect and interpret these effects which may otherwise produce erroneous intensity measurements. This observed phenomenon is analogous to beam hardening in x-ray tomography, which can lead to image artifacts without appropriate compensation. The peak shift toward longer wavelengths, and therefore lower energy photons, observed for NIR luminescent signals propagating through tissue may readily be described as a beam softening phenomenon.
Show PACS
87.15.mq, 33.20.Ea, 33.70.Jg, 33.50.Dq

Interstitial point radiance spectroscopy of turbid media

Lee C. L. Chin, Brendan Lloyd, William M. Whelan, and I. Alex Vitkin

J. Appl. Phys. 105, 102025 (2009) (11 pages)

Online Publication Date: 19 May 2009

Full Text: HTML | Sectioned HTML | PDF (986 kB)

Show Abstract
We present an optical technique, point radiance spectroscopy, to directly recover chromophore concentrations and the reduced optical scattering coefficient spectrum from continuous wave interstitial point radiance measurements at a single-source-detector separation in turbid, tissuelike media. The method employs a spectral algorithm to fit the relative radiance data, using the P3 approximation, at only two detection angles (0° and 90°). The spectral fitting algorithm is applied to simulated data of relative point fluence and relative point radiance data with added 1% noise and shows that even under realistic experimental conditions, only point radiance information is able to provide quantitative information regarding chromophore concentrations and scattering power at distances greater than two to three mean free paths from the source. Furthermore, experimental measurements in tissue-simulating phantoms demonstrate that dye concentrations and scattering parameters can be recovered to within ~10%. The developed point radiance technique bridges a technological gap between local surface reflectance and spatially resolved interstitial fluence methods in optical assessment of random media such as biological tissue.
Show PACS
87.64.kv, 87.50.wf, 87.85.-d, 82.70.-y, 82.80.-d

Characterization of integrating ultrasound detectors for photoacoustic tomography

G. Paltauf, R. Nuster, and P. Burgholzer

J. Appl. Phys. 105, 102026 (2009) (9 pages)

Online Publication Date: 19 May 2009

Full Text: HTML | Sectioned HTML | PDF (470 kB)

Show Abstract
Photoacoustic tomography is based on generation of sound waves in a semitransparent medium by illumination with short light pulses. In standard methods, measurements of the acoustic waves around the sample with point like ultrasound detectors are used for reconstruction of the distribution of absorbed energy, which contains information on light-absorbing structures such as blood vessels in tissue. Integrating ultrasound detectors are planes or lines larger than the imaged object and measure temporal signals that are given by spatial integrals over the sound field. It can be shown that such integrated signals give exact reconstructions with constant, high resolution throughout the imaging zone. The goal of the present study was to investigate with the help of simulations and experiments how far real implementations of integrating detectors based on piezoelectric films or optical interferometry have characteristics approximating those of ideal planes or lines. It is shown that the directive sensitivity of piezoelectric films tends to distort signals, mainly in the case of large area detectors. This distortion can, on the other hand, be used to directly measure a part of the directivity that is caused by distribution of stress components in the detector. Optical beams as part of an interferometer have omnidirectional response, but need focusing in order to achieve high temporal and spatial resolution. For example, with a beam focused to a diameter of 38  µm a spatial image resolution of 52  µm could be observed. Because of the beam waist, this resolution can only be achieved for acoustic sources lying within a range corresponding to the focal depth of the beam. It is concluded that line detectors made of piezoelectric thin films yield almost ideal performance for acoustic waves at normal incidence. Even better suited for photoacoustic tomography are focused optical beams as line detectors due to their omnidirectional response and higher signal to noise ratio, but only for objects with a size smaller than the focal depth.
Show PACS
87.63.dh, 43.80.Qf, 87.85.Ox, 87.57.cf, 87.63.L-

Noninvasive, in vivo imaging of the mouse brain using photoacoustic microscopy

Erich W. Stein, Konstantin Maslov, and Lihong V. Wang

J. Appl. Phys. 105, 102027 (2009) (5 pages)

Online Publication Date: 19 May 2009

Full Text: HTML | Sectioned HTML | PDF (406 kB)

Show Abstract
Noninvasive, high resolution imaging of mouse brain activity is poised to provide clinically translatable insights into human neurological disease progression. Toward noninvasive imaging of brain activity through the hemodynamic response, the dark-field photoacoustic microscopy (PAM) technique was enhanced to image the cortex vasculature of the mouse brain in vivo using endogenous hemoglobin contrast. Specifically, the PAM system was redesigned to efficiently collect photoacoustic waves originating from cortical vessels, providing high (70  µm lateral and 54  µm axial) resolution images of the mouse brain vasculature with a contrast-to-noise ratio of 25 dB. These findings confirm the efficacy of PAM to noninvasively image vascular structures in the mouse brain and the potential to image mouse brain function by tracking the hemodynamic response.
Show PACS
87.19.lh, 87.19.um, 87.63.dh, 87.64.M-, 87.57.cf, 87.14.E-

Noncontact imaging of absorption and scattering in layered tissue using spatially modulated structured light

Jessie R. Weber, David J. Cuccia, Anthony J. Durkin, and Bruce J. Tromberg

J. Appl. Phys. 105, 102028 (2009) (9 pages)

Online Publication Date: 19 May 2009

Full Text: HTML | Sectioned HTML | PDF (964 kB)

Show Abstract
Sinusoidal patterns of spatially modulated near-infrared (650 nm) structured light are used to interrogate multilayer phantoms and tissue. Diffuse reflectance is imaged at multiple spatial frequencies from 0–0.3  mm−1. ac and dc components of the image are fit to a two layer model formulated from the diffusion approximation to the Boltzman transport equation. The two-layer model depends on optical properties (absorption, µa, and reduced scattering, µ<sub>s</sub><sup>[prime]</sup>) in each layer and on top layer thickness (d). Layered tissue phantoms with variable optical properties in each layer (µa=0.006–0.034  mm−1 and µ<sub>s</sub><sup>[prime]</sup>=0.89–1.45  mm−1) were constructed to test the accuracy of the model. Constraining top layer thickness to within 25% of the correct value in a four-parameter fit results in recovery of upper layer optical properties with average accuracies of ±2% for top layer µ<sub>s</sub><sup>[prime]</sup> and ±17% for top layer µa. Bottom layer µa can then be recovered to an average accuracy of ±25% with two parameter fits. Average accuracies of top and bottom layer absorption can further be improved to 12% and 18%, respectively, by fitting for each alone. Bottom layer scattering and top layer thickness do not vary significantly from initial guesses because of poor sensitivity to these parameters in frequency dependent reflectance data. Measurements of in vivo volar forearm optical properties at 650 nm produced spatially varying skin (d=2  mm) optical property maps that range from 0.025–0.045 and 1.7–2  mm−1 for upper layer µa and µ<sub>s</sub><sup>[prime]</sup> and 0.005–0.015 and 0.5–3  mm−1 for lower layer µa and µ<sub>s</sub><sup>[prime]</sup>, respectively. These preliminary results suggest that spatial modulation of the source provides sufficient depth sensitivity to allow noncontact mapping and quantification of layered tissue optical properties using a wide-field, noncontact approach.
Show PACS
87.50.wf

Frequency-domain photothermoacoustics: Alternative imaging modality of biological tissues

Sergey Telenkov, Andreas Mandelis, Bahman Lashkari, and Michael Forcht

J. Appl. Phys. 105, 102029 (2009) (8 pages)

Online Publication Date: 19 May 2009

Full Text: HTML | Sectioned HTML | PDF (510 kB)

Show Abstract
Frequency-domain photothermoacoustic (FD-PTA) imaging of biological tissues is presented and compared with the conventional time-domain methodology. We demonstrate that tissue imaging can be performed with high axial resolution without the necessity to employ short-pulse and high peak-power laser systems to generate acoustic transients. The presented analysis shows that depth information in the FD-PTA method can be recovered by using linear frequency-modulated (chirped) optical excitation and frequency-domain signal processing algorithms. The signal-to-noise ratio can be increased significantly using correlation processing, which can compensate for the small amplitude of acoustic waves typical to the periodic excitation mode. Additionally, narrow-band signal demodulation enables depth-specific and confocal tissue imaging using the optically induced photothermoacoustic effect. Application of the FD-PTA is demonstrated in experiments with turbid phantoms and ex vivo tissue specimens.
Show PACS
87.63.L-, 87.50.wf, 43.35.Ud

Lateral spatial resolution of thermal lens microscopy during continuous scanning for nonstaining biofilm imaging

T. T. J. Rossteuscher, A. Hibara, K. Mawatari, and T. Kitamori

J. Appl. Phys. 105, 102030 (2009) (6 pages)

Online Publication Date: 19 May 2009

Full Text: HTML | Sectioned HTML | PDF (454 kB)

Show Abstract
The possible application of continuous scanning thermal lens microscopy (TLM) as alternative online biofilm observation method is studied. As biofilm is a heterogeneous sample, the influence of spatially limited thermal flow at the sample heterogeneities and the biofilm-environment border has to be considered. The influence of the edges on the lateral resolution with respect to scanning velocity during continuous scanning TLM was therefore evaluated. Lateral scanning experiments on 100 nm thin gold stripes showed that the maximum scan speed can be predicted from a time constant of a lock-in amplifier and the beamwidth. Since three-dimensional mapping is needed to fully characterize the biofilm structure, depth scanning experiments with stained 4  µm thick polystyrene samples with the coaxial TLM setup were evaluated for signal width at full width at half maximum. Thus, a minimum step width for depth scanning of 10  µm for observation has been acquired. A three-dimensional image of unstained biofilm grown in a flow chamber was acquired using continuous scanning TLM.
Show PACS
87.64.M-, 07.79.-v, 87.15.nr

Quantified light-induced fluorescence, review of a diagnostic tool in prevention of oral disease

Elbert de Josselin de Jong, Susan M. Higham, Philip W. Smith, Catherina J. van Daelen, and Monique H. van der Veen

J. Appl. Phys. 105, 102031 (2009) (7 pages)

Online Publication Date: 19 May 2009

Full Text: HTML | Sectioned HTML | PDF (381 kB)

Show Abstract
Diagnostic methods for the use in preventive dentistry are being developed continuously. Few of these find their way into general practice. Although the general trend in medicine is to focus on disease prevention and early diagnostics, in dentistry this is still not the case. Nevertheless, in dental research some of these methods seem to be promising for near future use by the general dental professional. In this paper an overview is given of a method called quantitative light-induced fluorescence or (QLF) in which visible and harmless light excites the teeth in the patient's mouth to produce fluorescent images, which can be stored on disk and computer analyzed. White spots (early dental caries) are detected and quantified as well as bacterial metabolites on and in the teeth. An overview of research to validate the technique and modeling to further the understanding of the technique by Monte Carlo simulation is given and it is shown that the fluorescence phenomena can be described by the simulation model in a qualitative way. A model describing the visibility of red fluorescence from within the dental tissue is added, as this was still lacking in current literature. An overview is given of the clinical images made with the system and of the extensive research which has been done. The QLFTM technology has been shown to be of importance when used in clinical trials with respect to the testing of toothpastes and preventive treatments. It is expected that the QLFTM technology will soon find its way into the general dental practice.
Show PACS
87.63.L-, 87.10.Rt

Discrete dipole approximation simulations of gold nanorod optical properties: Choice of input parameters and comparison with experiment

Constantin Ungureanu, Raja Gopal Rayavarapu, Srirang Manohar, and Ton G. van Leeuwen

J. Appl. Phys. 105, 102032 (2009) (7 pages)

Online Publication Date: 19 May 2009

Full Text: HTML | Sectioned HTML | PDF (921 kB)

Show Abstract
Gold nanorods have interesting optical properties due to surface plasmon resonance effects. A variety of biomedical applications of these particles have been envisaged and feasibilities demonstrated in imaging, sensing, and therapy based on the interactions of light with these particles. In order to correctly interpret experimental data and tailor the nanorods and their environments for optimal use in these applications, simulations of the optical properties of the particles under various conditions are essential. Of various numerical methods available, the discrete dipole approximation (DDA) approach implemented in the publicly available DDSCAT code is a powerful method that had proved popular for studying gold nanorods. However, there is as yet no universal agreement on the shape used to represent the nanorods and on the dielectric function of gold required for the simulations. We systematically study the influence of these parameters on simulated results. We find large variations in the position of plasmon resonance peaks, their amplitudes, and shapes of the spectra depending on the choice of the parameters. We discuss these in the light of experimental optical extinction spectra of gold nanorods synthesized in our laboratory. We show that much care should be taken and prudence applied before DDA results be used to interpret experimental data and to help characterize nanoparticles synthesized.
Show PACS
78.67.Bf, 73.20.Mf, 73.22.Lp, 78.20.Ci, 77.22.Ch, 87.85.Rs

Terahertz electromagnetic interactions with biological matter and their applications

Joo-Hiuk Son

J. Appl. Phys. 105, 102033 (2009) (10 pages)

Online Publication Date: 19 May 2009

Full Text: HTML | Sectioned HTML | PDF (1044 kB)

Show Abstract
The characteristics of electromagnetic interactions with biological matter in the terahertz region are reviewed. The recent development of terahertz technology has made possible the study of the scientifically rich spectral region where molecular rotational and vibrational modes exist. The technology is reviewed in terms of sources, detectors, and related techniques for spectroscopy and imaging. The spectroscopic technique has been utilized for the investigation of various biological molecules including DNAs, RNAs, nucleobases, proteins, polypeptides, and biological liquids to reveal intermolecular and intramolecular dynamics. Terahertz imaging has also proven to be a potential modality of medical diagnosis using the results of preliminary researches of skin and breast cancers.
Show PACS
87.57.-s, 87.14.gk, 87.14.E-, 33.15.Mt

A membrane basis for bacterial identification and discrimination using laser-induced breakdown spectroscopy

Steven J. Rehse, Narmatha Jeyasingham, Jonathan Diedrich, and Sunil Palchaudhuri

J. Appl. Phys. 105, 102034 (2009) (13 pages)

Online Publication Date: 19 May 2009

Full Text: HTML | Sectioned HTML | PDF (323 kB)

Show Abstract
Nanosecond single-pulse laser-induced breakdown spectroscopy (LIBS) has been used to discriminate between two different genera of Gram-negative bacteria and between several strains of the Escherichia coli bacterium based on the relative concentration of trace inorganic elements in the bacteria. Of particular importance in all such studies to date has been the role of divalent cations, specifically Ca2+ and Mg2+, which are present in the membranes of Gram-negative bacteria and act to aggregate the highly polar lipopolysaccharide molecules. We have demonstrated that the source of emission from Ca and Mg atoms observed in LIBS plasmas from bacteria is at least partially located at the outer membrane by intentionally altering membrane biochemistry and correlating these changes with the observed changes in the LIBS spectra. The definitive assignment of some fraction of the LIBS emission to the outer membrane composition establishes a potential serological, or surface-antigen, basis for the laser-based identification. E. coli and Pseudomonas aeruginosa were cultured in three nutrient media: trypticase soy agar as a control, a MacConkey agar with a 0.01% concentration of bile salts including sodium deoxycholate, and a trypticase soy agar with a 0.4% deoxycholate concentration. The higher concentration of deoxycholate is known to disrupt bacterial outer membrane integrity and was expected to induce changes in the observed LIBS spectra. Altered LIBS emission was observed for bacteria cultured in this 0.4% medium and laser ablated in an all-argon environment. These spectra evidenced a reduced calcium emission and in the case of one species, a reduced magnesium emission. Culturing on the lower (0.01%) concentration of bile salts altered the LIBS spectra for both the P. aeruginosa and two strains of E. coli in a highly reproducible way, although not nearly as significantly as culturing in the higher concentration of deoxycholate did. This was possibly due to the accumulation of divalent cations around the bacteria by the formation of an extracellular polysaccharide capsule. Lastly, a discriminant function analysis demonstrated that in spite of alterations in the LIBS spectrum induced by growth in the three different media, the analysis could correctly identify all samples better than 90% of the time. This encouraging result illustrates the potential utility of LIBS as a rapid bacteriological identification technology.
Show PACS
87.80.Dj, 87.16.dp, 87.14.-g, 87.15.N-

Biophysical mechanisms of modification of skin optical properties in the UV wavelength range with nanoparticles

A. P. Popov, A. V. Priezzhev, J. Lademann, and R. Myllylä

J. Appl. Phys. 105, 102035 (2009) (6 pages)

Online Publication Date: 19 May 2009

Full Text: HTML | Sectioned HTML | PDF (184 kB)

Show Abstract
In this paper, by means of the Mie theory and Monte Carlo simulations we investigate modification of optical properties of the superficial layer of human skin (stratum corneum) for 310- and 400-nm ultraviolet (UV) radiation by embedding of 35–200-nm-sized particles of titanium dioxide (TiO2) and silicon (Si). Problem of skin protection against UV light is of major importance due to increased frequency of skin cancer provoked by excessive doses of accepted UV radiation. For 310-nm light, the optimal sizes of the TiO2 and Si particles are found to be 62 and 55 nm, respectively, and for 400-nm radiation, 122 and 70 nm, respectively.
Show PACS
87.53.-j, 02.50.Ng, 87.19.xj, 87.85.Rs, 87.10.-e, 87.50.wf

Midinfrared surface-plasmon resonance: A novel biophysical tool for studying living cells

M. Golosovsky, V. Lirtsman, V. Yashunsky, D. Davidov, and B. Aroeti

J. Appl. Phys. 105, 102036 (2009) (11 pages)

Online Publication Date: 19 May 2009

Full Text: HTML | Sectioned HTML | PDF (1096 kB)

Show Abstract
We discuss the surface-plasmon resonance (SPR) technique based on Fourier transform infrared (FTIR) spectrometry. We explore the potential of the infrared surface plasmon technique for biological studies in aqueous solutions and compare it with the conventional surface plasmon technique operating in the visible range. We demonstrate that the sensitivity of the SPR technique in the infrared range is not lower and in fact is even higher. We show several examples of applying FTIR-SPR for biological studies: (i) monitoring D-glucose concentration in solution and (ii) measuring D-glucose uptake by erythrocytes in suspension. We emphasize the advantages of infrared SPR for studying living cell cultures and show how this technique can be used for characterization of (i) cholesterol penetration into plasma membrane and (ii) transferrin-induced clathrin-mediated endocytosis.
Show PACS
87.80.Dj, 87.16.D-, 82.80.-d, 87.64.km, 07.57.Ty, 87.18.-h

Laser interference microscopy in erythrocyte study

A. I. Yusipovich, E. Yu. Parshina, N. Yu. Brysgalova, A. R. Brazhe, N. A. Brazhe, A. G. Lomakin, G. G. Levin, and G. V. Maksimov

J. Appl. Phys. 105, 102037 (2009) (7 pages)

Online Publication Date: 19 May 2009

Full Text: HTML | Sectioned HTML | PDF (732 kB)

Show Abstract
With the laser interference microscopy (LIM) technique, one can measure phase height of cells—a variable proportional to the cell thickness and the difference in the refractive indices of the cell and the surrounding medium. This makes functional optical cell imaging possible, and estimation of shape, thickness, and area of erythrocytes feasible. In this paper, we studied changes in erythrocyte shape and volume with osmolarity and pH. Obtained from the LIM technique, erythrocyte phase heights and area values, as well as the hematocrit-measured erythrocyte volume, were used to estimate changes in the refractive index with osmolarity and pH. A comparison between the estimated refractive index with the refractive index, calculated in the assumption that it can only depend on the hemoglobin concentration in the cell, indicates that these two estimates are identical in the range of osmolarity (250–1000 mOsm) and pH (4.5–10.0) values. Thus, refractive index changes result exclusively from the changes in hemoglobin concentration with the changes in erythrocyte volume. Under these conditions, it is possible to estimate the amount of hemoglobin in an erythrocyte from its phase height and area, obtained from LIM.
Show PACS
87.64.M-, 87.63.lt, 42.62.Be

Possibility for a full optical determination of photodynamic therapy outcome

J. D. Vollet-Filho, P. F. C. Menezes, L. T. Moriyama, C. Grecco, C. Sibata, R. R. Allison, O. Castro e Silva, Jr., and V. S. Bagnato

J. Appl. Phys. 105, 102038 (2009) (7 pages)

Online Publication Date: 19 May 2009

Full Text: HTML | Sectioned HTML | PDF (492 kB)

Show Abstract
The efficacy of photodynamic therapy (PDT) depends on a variety of parameters: concentration of the photosensitizer at the time of treatment, light wavelength, fluence, fluence rate, availability of oxygen within the illuminated volume, and light distribution in the tissue. Dosimetry in PDT requires the congregation of adequate amounts of light, drug, and tissue oxygen. The adequate dosimetry should be able to predict the extension of the tissue damage. Photosensitizer photobleaching rate depends on the availability of molecular oxygen in the tissue. Based on photosensitizers photobleaching models, high photobleaching has to be associated with high production of singlet oxygen and therefore with higher photodynamic action, resulting in a greater depth of necrosis. The purpose of this work is to show a possible correlation between depth of necrosis and the in vivo photosensitizer (in this case, Photogem®) photodegradation during PDT. Such correlation allows possibilities for the development of a real time evaluation of the photodynamic action during PDT application. Experiments were performed in a range of fluence (0–450  J/cm2) at a constant fluence rate of 250  mW/cm2 and applying different illumination times (0–1800 s) to achieve the desired fluence. A quantity was defined (psi) as the product of fluorescence ratio (related to the photosensitizer degradation at the surface) and the observed depth of necrosis. The correlation between depth of necrosis and surface fluorescence signal is expressed in psi and could allow, in principle, a noninvasive monitoring of PDT effects during treatment. High degree of correlation is observed and a simple mathematical model to justify the results is presented.
Show PACS
87.50.wp, 42.62.Be, 87.50.wj, 87.50.wf

In situ real-time monitoring of biomolecular interactions by using surface infrared spectroscopy

Ayumi Hirano-Iwata, Ryo-taro Yamaguchi, Ko-ichiro Miyamoto, Yasuo Kimura, and Michio Niwano

J. Appl. Phys. 105, 102039 (2009) (11 pages)

Online Publication Date: 19 May 2009

Full Text: HTML | Sectioned HTML | PDF (1885 kB)

Show Abstract
This paper reviews our recent approaches for in situ label-free detection of biomolecules and their interactions by using infrared absorption spectroscopy (IRAS) in the multiple internal reflection (MIR) geometry. Biomolecular interactions, such as DNA hybridization, DNA hydration, protein-protein interaction, cell growth and cell death, were characterized and monitored in situ both in D2O and H2O media. Combination of MIR-IRAS and various sensing platforms, such as Si, GaAs, porous Si, and porous amunina, was also discussed in terms of sensitivity and applicability to chip analysis. It is demonstrated that MIR-IRAS is a promising tool not only for the label-free detection of biomolecules but also for the accurate discrimination between specific and nonspecific interactions, which is critically important when we are monitoring complex and dynamic biological samples.
Show PACS
87.15.K-, 87.64.km, 87.14.gk, 07.07.Df, 82.80.-d

Phase-sensitive swept source optical coherence tomography for imaging and quantifying of microbubbles in clear and scattering media

Ravi Kiran Manapuram, Venu Gopal Reddy Manne, and Kirill V. Larin

J. Appl. Phys. 105, 102040 (2009) (10 pages)

Online Publication Date: 19 May 2009

Full Text: HTML | Sectioned HTML | PDF (809 kB)

Show Abstract
A phase resolved system based on swept source optical coherence tomography (SSOCT) called as phase-sensitive SSOCT to detect and quantify gas microbubbles in aqueous and tissue simulated media is developed. The structural images of gas microbubbles are obtained using conventional SSOCT, while common path SSOCT was used to perform the phase-sensitive measurements. The system shows an axial resolution of 10  µm, a phase sensitivity of 0.03  rad, an imaging depth of up to 6  mm in air, and a scanning speed of 20  kHz for a single A-line. The structural images of the bubbles show an accuracy of 10  µm, whereas the temporal phase response show an accuracy of 0.01  µm. Images of rapidly moving bubbles are also presented which indicate that the SSOCT could be ultimately applied for the rapid assessment of microbubbles in biofluids and tissues.
Show PACS
87.63.L-, 42.30.Wb, 87.64.Cc, 47.63.-b, 87.19.rh

A review of some recent developments in polarization-sensitive optical imaging techniques for the study of articular cartilage

Stephen J. Matcher

J. Appl. Phys. 105, 102041 (2009) (11 pages)

Online Publication Date: 19 May 2009

Full Text: HTML | Sectioned HTML | PDF (791 kB)

Show Abstract
This article reviews recent developments in the optical imaging of articular cartilage using polarized-light methods, with an emphasis on tools that could be of use in tissue engineering approaches to treatment. Both second-harmonic generation microscopy and polarization-sensitive optical coherence tomography are described and their potential role in the treatment of cartilage disorders such as osteoarthritis is suggested. Key results are reviewed and future developments are discussed.
Show PACS
87.63.L-, 87.19.X-, 87.85.Lf, 42.65.Ky, 87.64.M-

Fully automated, quantitative, noninvasive assessment of collagen fiber content and organization in thick collagen gels

Christopher Bayan, Jonathan M. Levitt, Eric Miller, David Kaplan, and Irene Georgakoudi

J. Appl. Phys. 105, 102042 (2009) (11 pages)

Online Publication Date: 19 May 2009

Full Text: HTML | Sectioned HTML | PDF (1908 kB)

Show Abstract
Collagen is the most prominent protein of human tissues. Its content and organization define to a large extent the mechanical properties of tissue as well as its function. Methods that have been used traditionally to visualize and analyze collagen are invasive, provide only qualitative or indirect information, and have limited use in studies that aim to understand the dynamic nature of collagen remodeling and its interactions with the surrounding cells and other matrix components. Second harmonic generation (SHG) imaging emerged as a promising noninvasive modality for providing high-resolution images of collagen fibers within thick specimens, such as tissues. In this article, we present a fully automated procedure to acquire quantitative information on the content, orientation, and organization of collagen fibers. We use this procedure to monitor the dynamic remodeling of collagen gels in the absence or presence of fibroblasts over periods of 12 or 14 days. We find that an adaptive thresholding and stretching approach provides great insight to the content of collagen fibers within SHG images without the need for user input. An additional feature-erosion and feature-dilation step is useful for preserving structure and noise removal in images with low signal. To quantitatively assess the orientation of collagen fibers, we extract the orientation index (OI), a parameter based on the power distribution of the spatial-frequency-averaged, two-dimensional Fourier transform of the SHG images. To measure the local organization of the collagen fibers, we access the Hough transform of small tiles of the image and compute the entropy distribution, which represents the probability of finding the direction of fibers along a dominant direction. Using these methods we observed that the presence and number of fibroblasts within the collagen gel significantly affects the remodeling of the collagen matrix. In the absence of fibroblasts, gels contract, especially during the first few days, in a manner that allows the fibers to remain mostly disoriented, as indicated by small OI values. Subtle changes in the local organization of fibers may be taking place as the corresponding entropy values of these gels show a small decrease. The presence of fibroblasts affects the collagen matrix in a manner that is highly dependent on their number. A low density of fibroblasts enhances the rate of initial gel contraction, but ultimately leads to degradation of collagen fibers, which start to organize in localized clumps. This degradation and reorganization is seen within the first days of incubation with fibroblasts at a high density and is followed by de novo collagen fiber deposition by the fibroblasts. These collagen fibers are more highly oriented and organized than the fibers of the original collagen gel. These initial studies demonstrate that SHG imaging in combination with automated image analysis approaches offer a noninvasive and easily implementable method for characterizing important features of the content and organization of collagen in tissuelike specimens. Therefore, these studies could offer important insights for improving tissue engineering and disease diagnostic efforts.
Show PACS
87.63.lt, 42.65.Ky, 87.64.mk, 87.14.E-, 87.85.Lf

Controlled localization and enhanced gathering of particles on microfabricated concentrators assisted by ac-electro-osmosis

Laurent Tanguy and Liviu Nicu

J. Appl. Phys. 105, 102043 (2009) (8 pages)

Online Publication Date: 19 May 2009

Full Text: HTML | Sectioned HTML | PDF (513 kB)

Show Abstract
ac-electro-osmosis is used to concentrate particles on circular gold electrodes. Localization of the concentration of particles is predicted and experimentally observed by slight modifications of the electrical parameters (frequency, voltage intensity). Efficiency evaluations of the concentrators are proposed and applied to our system and compared with the predictions. Experimental concentration on dedicated test devices is 200 times faster than classical diffusion. An optimization of the collection rate is obtained by switching the frequency signal between two determined values. This optimization allows doubling the arrival rate of particles.
Show PACS
82.39.Wj, 82.45.Fk

Electric-field-induced interaction between biological cells or colloidal particles

W. J. Tian, J. P. Huang, and K. W. Yu

J. Appl. Phys. 105, 102044 (2009) (6 pages)

Online Publication Date: 19 May 2009

Full Text: HTML | Sectioned HTML | PDF (303 kB)

Show Abstract
Biological cells can be treated as an inhomogeneous particle. In addition to biomaterials, inhomogeneous particles are also important in more traditional colloidal science. By using two energy methods that are based on Legendre polynomials and Green's function, respectively, we investigate the interaction between biological cells or colloidal particles in the presence of an external electric field, in an attempt to investigate the effect of inhomogeneity on crossover frequencies across which the interaction force changes from attraction to repulsion or vice versa. The predictions by the two methods agree with each other very well. It is shown that there exist two kinds of crossover frequencies omegap, one from attraction to repulsion and the other from repulsion to attraction as external frequencies increase. The first omegap strongly depends on the degree of inhomogeneity, while the second omegap does not. This work has relevance to manipulation of biological cells or colloidal particles.
Show PACS
87.50.C-, 82.70.Dd, 02.30.-f, 02.10.De

Does the deoxyribonucleic acid shape dictate its conductivity?

P. Romano, A. Polcari, V. Granata, L. Sabatino, and V. Colantuoni

J. Appl. Phys. 105, 102045 (2009) (5 pages)

Online Publication Date: 19 May 2009

Full Text: HTML | Sectioned HTML | PDF (1013 kB)

Show Abstract
We present the evolution of current-voltage characteristics measured on linear fragments of deoxyribonucleic acid (DNA) molecules as a function of their length. The nonlinear behavior systematically observed at room temperature and also reported on circular plasmids suggests that the more molecules are involved in the conduction process, the higher are the current values measured. At the same time, a characteristic steplike feature superimposed to an overall increasing background appears more pronounced. We interpret this behavior in terms of simultaneous coherent and incoherent transport processes, the former taking place inside the DNA molecule, the latter through the network of molecules. Following our previous analysis on circular molecules, a phenomenological model is developed, in which a tunneling current with an energy dependent transmission coefficient is superimposed to a hopping current. The model provides a semiquantitative evidence that the steplike feature represents the signature of charge transmission inside the molecule. Our results are consistent with many of the conductivity data present in the literature.
Show PACS
87.15.Pc, 87.14.gk, 87.18.-h

Device considerations for development of conductance-based biosensors

Kangho Lee, Pradeep R. Nair, Adina Scott, Muhammad A. Alam, and David B. Janes

J. Appl. Phys. 105, 102046 (2009) (13 pages)

Online Publication Date: 19 May 2009

Full Text: HTML | Sectioned HTML | PDF (655 kB)

Show Abstract
Design and fabrication of electronic biosensors based on field-effect-transistor (FET) devices require understanding of interactions between semiconductor surfaces and organic biomolecules. From this perspective, we review practical considerations for electronic biosensors with emphasis on molecular passivation effects on FET device characteristics upon immobilization of organic molecules and an electrostatic model for FET-based biosensors.
Show PACS
87.85.Ox, 68.47.Fg, 85.30.Tv

Emerging technologies for diagnosis of dental caries: The road so far

Bennett T. Amaechi

J. Appl. Phys. 105, 102047 (2009) (9 pages)

Online Publication Date: 19 May 2009

Full Text: HTML | Sectioned HTML | PDF (138 kB)

Show Abstract
It is now universally recognized that the development of new technologies for early detection and quantitative monitoring of dental decay at an early stage of formation could provide health and economic benefits ranging from timely preventive interventions to reduction in the time required for clinical trials of anticaries agents. The use of technologies as adjunct to clinical visual examination for caries diagnosis will facilitate preventive care in dentistry to lower treatment cost as well as reduce the cost and time for testing potential anticaries agents. This article describes the various technologies available to aid the dental practitioners in detecting dental caries at the earliest stage of its formation, assessing the activities of the detected carious lesion, and quantitatively or qualitatively monitoring of the lesion over time. The need and the importance of these technologies were also discussed. The data discussed are primarily based on published scientific studies and reviews from case reports, clinical trials, and in vitro and in vivo studies. References have been traced manually by MEDLINE® or through manufacturer's websites. While some of the devices are fully developed and commercially available, others are still under development. The devices vary in their modes of action as well as their capability as caries diagnostic aids. It is clear that the differences in caries presentations and behavior in different anatomical sites make it unlikely that any one diagnostic modality will have adequate sensitivity and specificity of detection of carious lesions for all sites; a combination of diagnostic tools will help us diagnose lesions earlier and detect failing restorations sooner, all to avoid more costly, destructive dental procedures and truly take dentistry into the preventive rather than the reactive mode.
Show PACS
87.85.Ox

Application of biophysical technologies in dental research

Susan M. Higham, Neil Pender, Elbert de Josselin de Jong, and Philip W. Smith

J. Appl. Phys. 105, 102048 (2009) (8 pages)

Online Publication Date: 19 May 2009

Full Text: HTML | Sectioned HTML | PDF (562 kB)

Show Abstract
There is a wealth of evidence to indicate that if dental caries can be recognized at an early stage, it is possible to halt its progression or even reverse it. This has led to an increased interest in the development of diagnostic techniques capable of visualizing caries at an early stage in addition to providing clinicians with an aid to diagnosis. Several techniques are available for research and clinical applications for detecting early demineralization. This manuscript has reviewed some of the techniques currently available to determine their advantages, whether they have any limitations and their applicability to dental research and clinical dentistry. Not one method is the perfect choice in all situations, but what is clear is that the development and application of biophysical technologies have allowed major advances to be made in dental research as well as in clinical dentistry. With continued developments these technologies will play an important role in the future management of dental disease.
Show PACS
87.63.L-, 87.19.X-
back to top

LASERS, OPTICS, AND OPTOELECTRONICS

Theoretical studies of the optical properties of plasmon resonance on silver nanoparticles in the near-field optics

Ye-Wan Ma, Yu Zhang, Zhao-Wang Wu, Li-Hua Zhang, Jie Zhang, Guo-Shu Jian, and Shi-Fa Wu

J. Appl. Phys. 105, 103101 (2009) (6 pages)

Online Publication Date: 18 May 2009

Full Text: HTML | Sectioned HTML | PDF (445 kB)

Show Abstract
Near-field spectral characteristics, images, and optical parameters of silver nanoparticles are studied using Green's tensor. The Lippmann–Schwinger integral equation is discretized, and numerically solved with complex-conjugate gradient method-fast Fourier transform algorithm. Simulation models include placing nanoparticles in either an infinitely homogeneous medium or on a substrate, and illuminated either directly with plane waves or through a glass substrate under total internal reflection. Simulation results suggest that local plasmon resonance redshifts to longer wavelengths when dielectric constant of the surrounding medium increases or when a substrate is presented, but blueshifts to shorter wavelengths when the height of a nanoparticle increases. Due to the exponential attenuation behavior of evanescent waves, total intensity of electrical field attenuates quickly as the detection distance increases. Optical efficiencies, scattering efficiencies, absorption, and extinction efficiencies of Ag nanoparticles are also reported.
Show PACS
78.67.Bf, 78.20.Ci

Comparison of output power of InGaN laser diodes for different Al compositions in the AlGaN n-cladding layer

H. Y. Ryu, K. H. Ha, J. K. Son, H. S. Paek, Y. J. Sung, K. S. Kim, H. K. Kim, Y. Park, S. N. Lee, and O. H. Nam

J. Appl. Phys. 105, 103102 (2009) (4 pages)

Online Publication Date: 20 May 2009

Full Text: HTML | Sectioned HTML | PDF (171 kB)

Show Abstract
The output power of InGaN multiple-quantum-well laser diodes (LDs) emitting at 405 nm wavelength is compared for several Al composition in the AlGaN n-cladding layer. The Al composition has been varied from 2% to 6% to study the effect of n-cladding refractive index on threshold current and slope efficiency of the LDs. As the Al composition in the AlGaN n-cladding layer increases, both threshold current and slope efficiency decrease. This behavior can be explained by the change in optical field distribution with refractive index of the AlGaN n-cladding layer. It is found that the Al composition of <=4% would be advantageous for achieving more than 100 mW output power and high level of catastrophic optical damage.
Show PACS
42.55.Px, 42.81.Bm, 42.25.-p

Semiconductor-based superlens for subwavelength resolution below the diffraction limit at extreme ultraviolet frequencies

M. A. Vincenti, A. D'Orazio, M. G. Cappeddu, Neset Akozbek, M. J. Bloemer, and M. Scalora

J. Appl. Phys. 105, 103103 (2009) (6 pages)

Online Publication Date: 20 May 2009

Full Text: HTML | Sectioned HTML | PDF (491 kB)

Show Abstract
We theoretically demonstrate negative refraction and subwavelength resolution below the diffraction limit in the UV and extreme UV ranges using semiconductors. The metal-like response of typical semiconductors such as GaAs or GaP makes it possible to achieve negative refraction and superguiding in resonant semiconductor/dielectric multilayer stacks, similar to what has been demonstrated in metallodielectric photonic band gap structures. The exploitation of this basic property in semiconductors raises the possibility of yet-untapped applications in the UV and soft x-ray ranges.
Show PACS
42.79.Dj, 42.25.-p, 42.70.Qs

Interfacial misfit array formation for GaSb growth on GaAs

Shenghong Huang, Ganesh Balakrishnan, and Diana L. Huffaker

J. Appl. Phys. 105, 103104 (2009) (5 pages)

Online Publication Date: 20 May 2009

Full Text: HTML | Sectioned HTML | PDF (652 kB)

Show Abstract
The manuscript reports that the initial strain relaxation of highly mismatched GaSb layers grown on GaAs (001) is governed by the two-dimensional (2D), periodic interfacial misfit (IMF) dislocation array growth mode. Under optimized growth conditions, only pure 90° dislocations are generated along both [110] and [1[overline 1]0] directions that are located at GaSb/GaAs interface, which leads to very low threading dislocation density propagated along the growth direction. The long-range uniformity and subsequent strain relaxation of the 2D and periodic IMF array are demonstrated via transmission electron microscopy and scanning transmission electron microscopy images at GaSb/GaAs interface.
Show PACS
61.72.Ff, 62.40.+i

Restoration of terahertz signals distorted by atmospheric water vapor absorption

Yingxin Wang, Zhiqiang Chen, Ziran Zhao, Li Zhang, Kejun Kang, and Yan Zhang

J. Appl. Phys. 105, 103105 (2009) (7 pages)

Online Publication Date: 21 May 2009

Full Text: HTML | Sectioned HTML | PDF (242 kB)

Show Abstract
Terahertz spectroscopic measurements under ordinary atmospheric conditions may suffer interferences from water vapor absorption in the ambient air. A manifold of narrow absorption lines appears in the terahertz spectrum at particular frequencies corresponding to the pure rotational transitions of water molecules. For real-world data, such effect results in unwanted spectral artifacts in the deconvolved spectrum of the examined sample and thus complicates its frequency-dependent characterization. In this paper we use a signal postprocessing algorithm consisting of line shape fitting and spectral subtraction procedures to eliminate the water lines. Restoration of terahertz signals from simulated data and low-humidity measurements is first demonstrated to validate the algorithm. Furthermore, to overcome the difficulty of eliminating strong lines which lead to possible excessive absorption under high-humidity environment, we propose to modify the objective function in spectral subtraction by smoothing the residual spectrum to get acceptable performance.
Show PACS
33.20.Bx, 33.20.Sn

Absolute measurement of the nonlinear refractive indices of reference materials

Georges Boudebs and Kamil Fedus

J. Appl. Phys. 105, 103106 (2009) (5 pages)

Online Publication Date: 21 May 2009

Full Text: HTML | Sectioned HTML | PDF (237 kB)

Show Abstract
We report absolute measurements of the nonlinear refractive index on carbon disulfide (CS2) and fused silica. These materials are commonly used as standard references in nonlinear optical experiments. To obtain more accurate values than those usually used, we have combined the z-scan method inside a 4-f imaging system (in order to analyze the spatial distortion of the diffracted pump beam) with the “Kerr shutter” experiment (to evaluate the temporal pulse width durations for three different wavelengths such as 1064, 532, and 355 nm). We obtained surprisingly n2 values one order of magnitude less than the one usually taken into account in the picosecond regime and a more significant dispersion of the nonlinear refraction index. Experimental and simulated Z-scan transmittance profiles as well as acquired autocorrelation functions in the Kerr-gating experiments are presented here in order to validate our measurements.
Show PACS
78.20.Ci

Narrow asymmetric waveguide semiconductor lasers for improved temperature wavelength stability

Boris Ryvkin and Eugene Avrutin

J. Appl. Phys. 105, 103107 (2009) (4 pages)

Online Publication Date: 21 May 2009

Full Text: HTML | Sectioned HTML | PDF (441 kB)

Show Abstract
We show theoretically that Fabry–Pérot semiconductor lasers using narrow asymmetric waveguides can offer much higher temperature stability of the lasing wavelength compared to structures with standard symmetrical waveguides. The mechanism of the low thermal sensitivity is the uniquely strong wavelength dependence of the confinement factor near the waveguide cutoff, which increases the blueshift of the modal gain peak with carrier density and helps offset the bandgap shrinkage with temperature.
Show PACS
42.55.Px, 42.60.Lh, 42.60.Jf

Well-width dependence of in-plane optical anisotropy in (001) GaAs/AlGaAs quantum wells induced by in-plane uniaxial strain and interface asymmetry

C. G. Tang, Y. H. Chen, B. Xu, X. L. Ye, and Z. G. Wang

J. Appl. Phys. 105, 103108 (2009) (6 pages)

Online Publication Date: 22 May 2009

Full Text: HTML | Sectioned HTML | PDF (569 kB)

Show Abstract
The well-width dependence of in-plane optical anisotropy (IPOA) in (001) GaAs/AlxGa1−xAs quantum wells induced by in-plane uniaxial strain and interface asymmetry has been studied comprehensively. Theoretical calculations show that the IPOA induced by in-plane uniaxial strain and interface asymmetry exhibits much different well-width dependence. The strain-induced IPOA is inversely proportional to the energy spacing between heavy- and light-hole subbands, so it increases with the well width. However, the interface-related IPOA is mainly determined by the probability that the heavy- and light-holes appear at the interfaces, so it decreases with the well width. Reflectance difference spectroscopy has been carried out to measure the IPOA of (001) GaAs/AlxGa1−xAs quantum wells with different well widths. Strain- and interface-induced IPOA have been distinguished by using a stress apparatus, and good agreement with the theoretical prediction is obtained. The anisotropic interface potential parameters are also determined. In addition, the energy shift between the interface- and strain-induced 1H1E reflectance difference (RD) structures, and the deviation of the 1L1E RD signal away from the prediction of the calculation model have been discussed.
Show PACS
78.67.De

Effects of defect permittivity on resonant frequency and mode shape in the three-dimensional woodpile photonic crystal

Daniel Stieler, Anthony Barsic, Gary Tuttle, Ming Li, and Kai-Ming Ho

J. Appl. Phys. 105, 103109 (2009) (4 pages)

Online Publication Date: 22 May 2009

Full Text: HTML | Sectioned HTML | PDF (671 kB)

Show Abstract
Tuning the resonant frequency of a 1  uc defect across the bandgap of a three-dimensional woodpile photonic crystal (PC) was achieved by altering the defect's permittivity. Experiments were performed at microwave frequencies and calculations were made using the transfer-scattering matrix method. Defect permittivity was varied by using solid materials of different permittivities or by constructing structures smaller than a lattice constant from the the PC lattice materials. These small structures, which will be referred to as “sublattice defects,” produce an effective permittivity between their two materials' permittivities. Changes in mode shape with resonant frequency and permittivity were also examined.
Show PACS
42.70.Qs, 77.22.Ch

Transmittance and optical constants of Tm films in the 2.75–1600 eV spectral range

Manuela Vidal-Dasilva, Mónica Fernández-Perea, José A. Aznárez, Juan I. Larruquert, José A. Méndez, Luca Poletto, A. Marco Malvezzi, Angelo Giglia, and Stefano Nannarone

J. Appl. Phys. 105, 103110 (2009) (7 pages)

Online Publication Date: 26 May 2009

Full Text: HTML | Sectioned HTML | PDF (656 kB)

Show Abstract
The optical constants of thulium (Tm) films were obtained in the 2.75–1600 eV range from transmittance measurements performed at room temperature. Thin films of Tm were deposited by evaporation in ultrahigh vacuum conditions and their transmittance was measured in situ. Tm films were deposited onto grids coated with a thin, C support film. Transmittance measurements were used to obtain the optical extinction coefficient k of Tm films. The refractive index n of Tm was calculated using the Kramers–Krönig analysis. k data were extrapolated both on the high and the low energy sides by using experimental and calculated extinction coefficient values available in the literature. Tm, similar to other lanthanides, has a low-absorption band below the O2,3 edge onset; the lowest absorption was measured at ~23  eV. Therefore, Tm is a promising material for filters and multilayer coatings in the energy range below the O2,3 edge in which materials typically have an absorption stronger than away. Good consistency of the data was obtained through f and inertial sum rules.
Show PACS
78.20.Ci, 81.15.Ef, 78.66.Bz, 78.40.Kc, 68.65.Ac, 68.55.jd

Physical characterization of n-GaAs on p-Si formed by low-temperature pulsed-laser deposition

K. P. Acharya, H. Khatri, and B. Ullrich

J. Appl. Phys. 105, 103111 (2009) (5 pages)

Online Publication Date: 27 May 2009

Full Text: HTML | Sectioned HTML | PDF (380 kB)

Show Abstract
Stoichiometry, texture, surface features, I-V characteristic, and optical responsivity were studied of thin-film n-GaAs deposited onto p-type Si at room temperature. Low-temperature pulsed-laser deposition using a neodymium doped yttrium aluminum garnet laser (532 nm, 6 ns, 10 Hz) was employed to form the heteropairing. The film is stoichiometric, mainly of amorphous nature including some crystalline sections, and, despite droplets, exhibits an optically smooth surface. Rectification and photodiode properties for alternating as well as direct current experiments were established in an almost scholastic manner, which cannot be attributed to the previously investigated p-GaAs/n-Si. Hence, the ablation of electron rich GaAs is apparently the way of choice to form operative GaAs/Si junction devices. The work further reveals that intrinsic sample features might be different for alternating and direct photocurrent measurements.
Show PACS
73.40.Kp, 81.15.Fg, 61.50.Nw, 81.40.Ef, 68.55.ag, 73.40.Ei, 73.50.Pz

Experimental study on electromagnetic wave transparency for coated metallic cylinders

Xiaobing Cai, Qibo Deng, and Gengkai Hu

J. Appl. Phys. 105, 103112 (2009) (5 pages)

Online Publication Date: 27 May 2009

Full Text: HTML | Sectioned HTML | PDF (303 kB)

Show Abstract
In this work, coated metallic cylinders transparent to electromagnetic waves are designed based on the neutral inclusion method; they are then verified experimentally by measuring the reflection coefficient and total scattering fields. The dynamic effective permittivity of a composite made of coated metallic cylinders is first derived by setting the effective permittivity of the composite equals to that of air; the necessary dielectric constant of the coating layer as function of the geometry of the coated cylinder is obtained. We choose the mixture of carbon nanotube (CNT) and rubber for the coating material, its dielectric constant can be tuned by adjusting the content of CNT to reach the value necessary for realizing the transparency. The reflection coefficients and the total scattering electric fields are measured for the carefully designed coated and bare copper cylinders, respectively, significant reductions of the reflection coefficient and total scattering fields are observed for the coated cylinders, which confirms the proposed design method.
Show PACS
78.20.Ci, 77.22.Ch

Energy transfer between Yb3+ and Er3+ in barium gallogermanate glass

X. P. Jiang, Z. M. Yang, T. Liu, and S. H. Xu

J. Appl. Phys. 105, 103113 (2009) (6 pages)

Online Publication Date: 27 May 2009

Full Text: HTML | Sectioned HTML | PDF (662 kB)

Show Abstract
Spectroscopic properties of Er3+/Yb3+ codoped barium gallogermanate glass demonstrate that an efficient energy transfer from Yb3+ to Er3+ ions occurs while the back energy transfer from Er3+ to Yb3+ ions cannot be ignored. Based on the rate equations of electron transitions, the forward energy transfer Yb3+(2F5/2)+Er3+(4I15/2)-->Yb3+(2F7/2)+Er3+(4I11/2) and the back transfer Er3+(4I11/2)+Yb3+(2F7/2)-->Er3+(4I15/2)+Yb3+(2F5/2) coefficients were calculated to be 9.2×10−17  cm3 s−1 and 1.1×10−17  cm3 s−1, respectively. Also the energy transfer upconversion coefficient Yb3+(2F5/2)+Er3+(4I11/2)-->Yb3+(2F7/2)+Er3+(2F7/2) was determined to be 1.1×10−16  cm3 s−1. The calculated results show that a population inversion between the 4I13/2 and 4I15/2 levels can be attained at a low pumping flux of around 1.7×1022  cm−2 s−1, while the inversion threshold between the 4S3/2 and 4I15/2 levels is about 30 times higher when pumped by 980 nm laser diode. With increasing pump flux the back energy transfer probability becomes larger and when the pump flux is more than 2.0×1022  cm−2 s−1, the back energy transfer probability dominates the forward energy transfer probability.
Show PACS
78.66.Jg, 78.55.Qr, 78.45.+h, 71.23.Cq, 61.72.up

Direct evidence for electric field assisted dissolution of Au nanoparticles on glass surface

Zhiyu Zou, Qiang Wang, Xiangjun Chen, and Shiliang Qu

J. Appl. Phys. 105, 103114 (2009) (7 pages)

Online Publication Date: 28 May 2009

Full Text: HTML | Sectioned HTML | PDF (662 kB)

Show Abstract
Spherical gold (Au) nanoparticles are formed onto glass surface by sputtering of Au foil and the following annealing process. By employing electric field assisted annealing of above as-prepared samples, the original spherical Au nanoparticles are dissolved to lunar-eclipselike structure and even fully dissolved. When applied voltages are increased in steplike feature, spikelike sharp current increase is observed at every voltage step, and it is followed by a rather long current decaying process. The spikelike current increase indicates the onset of electronic transport, leading to Au nanoparticles polarization and ionization. Long current decaying process is assigned to the electronic conduction from cathode to recombine with as-ionized positive charges, along with Au cationic transport resulting in dissolution of Au atoms from the nanoparticles. Our current study provides straightforward evidence of electric field assisted dissolution of Au nanoparticles on glass surface.
Show PACS
64.75.Bc, 81.40.Ef, 79.20.Rf, 81.16.-c, 73.63.Bd
back to top

PLASMAS AND ELECTRICAL DISCHARGES

Three-dimensional model of magnetized capacitively coupled plasmas

Shahid Rauf, Jason Kenney, and Ken Collins

J. Appl. Phys. 105, 103301 (2009) (9 pages)

Online Publication Date: 20 May 2009

Full Text: HTML | Sectioned HTML | PDF (1139 kB)

Show Abstract
A three-dimensional plasma model is used to understand the characteristics of magnetized capacitively coupled plasma discharges. The simulations consider plasmas generated using high frequency (13.5 MHz) and very high frequency (162 MHz) sources, electropositive (Ar) and electronegative (O2) gases, and spatially uniform and nonuniform magnetic fields. Application of a magnetic field parallel to the electrodes is found to enhance the plasma density due to improved electron confinement and shift the plasma due to the E×B drift. The plasma is electrically symmetric at 162 MHz so it drifts in opposite directions adjacent to the two electrodes due to the E×B drift. On the other hand, the 13.5 MHz plasma is electrically asymmetric and it predominantly moves in one direction under the influence of the E×B drift. The E×B drift focuses the plasma into a smaller volume in regions with convex magnetic field lines. Conversely, the E×B drift spreads out the plasma in regions with concave magnetic field lines. In a magnetized O2 plasma, the overall plasma is found to move in one direction due to the E×B drift while the plasma interior moves in the opposite direction. This behavior is linked to the propensity of negative ions to reside in regions of peak plasma potential, which moves closer to the chamber center opposite to the E×B drift direction.
Show PACS
52.50.Dg, 52.80.Pi, 52.25.Xz, 52.25.Fi, 52.65.Kj

Effects of rf power on electron density and temperature, neutral temperature, and Te fluctuations in an inductively coupled plasma

James Camparo and Gilda Fathi

J. Appl. Phys. 105, 103302 (2009) (9 pages)

Online Publication Date: 21 May 2009

Full Text: HTML | Sectioned HTML | PDF (483 kB)

Show Abstract
Atomic clocks that fly on global-navigation satellites such as global positioning system (GPS) and Galileo employ light from low-temperature, inductively coupled plasmas (ICPs) for atomic signal generation and detection (i.e., alkali/noble-gas rf-discharge lamps). In this application, the performance of the atomic clock and the capabilities of the navigation system depend sensitively on the stability of the ICP's optical emission. In order to better understand the mechanisms that might lead to instability in these rf-discharge lamps, and hence the satellite atomic clocks, we studied the optical emission from a Rb/Xe ICP as a function of the rf power driving the plasma. Surprisingly, we found that the electron density in the plasma was essentially independent of increases in rf power above its nominal value (i.e., “rf-power gain”) and that the electron temperature was only a slowly varying function of rf-power gain. The primary effect of rf power was to increase the temperature of the neutrals in the plasma, which was manifested by an increase in Rb vapor density. Interestingly, we also found evidence for electron temperature fluctuations (i.e., fluctuations in the plasma's high-energy electron content). The variance of these fluctuations scaled inversely with the plasma's mean electron temperature and was consistent with a simple model that assumed that the total electron density in the discharge was independent of rf power. Taken as a whole, our results indicate that the electrons in alkali/noble-gas ICPs are little affected by slight changes in rf power and that the primary effect of such changes is to heat the plasma's neutral species.
Show PACS
52.50.Dg, 52.80.Pi, 52.25.Ya, 52.25.Gj, 52.25.Os, 52.35.Qz

The role of He in enhancing the intensity and lifetime of H and D emissions from laser-induced atmospheric-pressure plasma

Koo Hendrik Kurniawan, Tjung Jie Lie, Maria Margaretha Suliyanti, Rinda Hedwig, Marincan Pardede, Muliadi Ramli, Hideaki Niki, Syahrun Nur Abdulmadjid, Nasrullah Idris, Kurnia Lahna, Yoshihumi Kusumoto, Kiichiro Kagawa, and May On Tjia

J. Appl. Phys. 105, 103303 (2009) (6 pages)

Online Publication Date: 22 May 2009

Full Text: HTML | Sectioned HTML | PDF (396 kB)

Show Abstract
A series of measurements have been performed on the time dependences of the intensities of helium, hydrogen, and deuterium emission lines from the corresponding laser-induced helium plasma at atmospheric pressure for two different He flow rates. The prolonged Halpha and Hbeta emissions along with their constant intensity ratio over a relatively extended period indicate the need to provide an alternative excitation mechanism other than the well-known thermal excitation process in a hot plasma. This additional excitation mechanism is also related to the metastable excited state of a He atom as indicated by the similar characteristics of the observed time dependence of the emission intensities. The enhanced intensity and lifetime of He emission at a high He flow rate was explained in terms of the collision-induced increase in the number of He atoms excited to above the 2 1S0 metastable state, which was also responsible for the delayed excitation of H and D atoms via an energy transfer mechanism involving a Penning-like chemi-ionization process. Finally, the benefits of He-assisted delayed excitation of H and D atoms and the aforementioned enhanced intensity and lifetime at a high He flow rate were demonstrated by the achievement of clearly resolved Halpha and Dalpha emission lines.
Show PACS
52.25.Os, 52.50.Jm, 52.70.Kz, 52.20.Hv, 52.80.Sm, 52.25.Jm

Laser ablation of aluminum from normal evaporation to phase explosion

A. Gragossian, S. H. Tavassoli, and B. Shokri

J. Appl. Phys. 105, 103304 (2009) (7 pages)

Online Publication Date: 26 May 2009

Full Text: HTML | Sectioned HTML | PDF (323 kB)

Show Abstract
A study of laser ablation of Aluminum sample by nanosecond laser pulses considering two simultaneous mechanisms of normal evaporation and phase explosion is theoretically carried out. The temperature distribution in the sample is calculated by a one dimensional heat conduction equation. Ablation depth due to the evaporation and explosion is calculated as a function of laser pulse energies. Variation in some effective sample parameters during the laser ablation and their effects on laser ablation mechanisms are taken into account. At low irradiance, ablation is mainly due to the evaporation, while after a threshold intensity, the phase explosion becomes the dominant mechanism. Theoretical results of transition from the normal evaporation to the phase explosion are in good agreement with the experimental results.
Show PACS
79.20.Ds, 64.70.fm, 72.15.Cz, 61.80.Ba

Fast discharge in a plasma gun with hemispherical insulator

P. S. Antsiferov, L. A. Dorokhin, Yu. V. Sidelnikov, and K. N. Koshelev

J. Appl. Phys. 105, 103305 (2009) (3 pages)

Online Publication Date: 28 May 2009

Full Text: HTML | Sectioned HTML | PDF (228 kB)

Show Abstract
A method of creation of hot dense plasma is proposed. It is based on cumulation of a shockwave, which originates on a hemispherical surface of insulator of plasma gun. The results of first experiments are presented. The shock wave is driven by fast electrical discharge (dI/dt>1012  A/s). The inductive storage with semiconductor opening switch is used as a current driver. Time resolved pin-hole images and vacuum ultraviolet (vuv) spectra are studied. Shockwaves from hemispherical insulator with 4 mm radius create plasma with a form of column about 1 mm diameter and 3–4 mm length. vuv spectra contain the lines of Ar ions that corresponds to the electron temperature about 20 eV. Possible practical application is discussed.
Show PACS
52.50.Lp, 52.35.Tc, 52.25.Os, 52.80.-s, 52.75.-d

Static gas-liquid interfacial direct current discharge plasmas using ionic liquid cathode

T. Kaneko, K. Baba, and R. Hatakeyama

J. Appl. Phys. 105, 103306 (2009) (5 pages)

Online Publication Date: 28 May 2009

Full Text: HTML | Sectioned HTML | PDF (222 kB)

Show Abstract
Due to the unique properties of ionic liquids such as their extremely low vapor pressure and high heat capacity, we have succeeded in creating the static and stable gas (plasmas)-liquid (ionic liquids) interfacial field using a direct current discharge under a low gas pressure condition. It is clarified that the ionic liquid works as a nonmetal liquid electrode, and furthermore, a secondary electron emission coefficient of the ionic liquid is larger than that of conventional metal electrodes. The plasma potential structure of the gas-liquid interfacial region, and resultant interactions between the plasma and the ionic liquid are revealed by changing a polarity of the electrode in the ionic liquid. By utilizing the ionic liquid as a cathode electrode, the positive ions in the plasma region are found to be irradiated to the ionic liquid. This ion irradiation causes physical and chemical reactions at the gas-liquid interfacial region without the vaporization of the ionic liquid.
Show PACS
52.80.Wq, 52.80.Vp, 82.33.Xj, 82.45.Fk, 61.80.Jh
back to top

STRUCTURAL, MECHANICAL, THERMODYNAMIC, AND OPTICAL PROPERTIES OF CONDENSED MATTER

Solution-processed omnidirectional antireflection coatings on amorphous silicon solar cells

Yuehui Wang, Rajesh Tummala, L. Chen, L. Qing Guo, Weidong Zhou, and Meng Tao

J. Appl. Phys. 105, 103501 (2009) (6 pages)

Online Publication Date: 18 May 2009

Full Text: HTML | Sectioned HTML | PDF (903 kB)

Show Abstract
Solution-processed spherical surface textures are demonstrated on commercial amorphous silicon solar cells. The texture is formed with a monolayer of silica microspheres by convective coating, followed by a spin-on-glass film. It is found that the spherical texture reduces the reflectivity of the cells in the wavelength regime of 400–1200 nm, thus broad spectrum. It is also found that the spherical texture improves the efficiency of the cells at various incident angles from surface normal to at least 60°. The improvement in efficiency increases at larger incident angles to as high as 12% relative improvement, demonstrating its omnidirectionality. Current-voltage characteristics show that the efficiency improvement with coating is largely due to the increased short circuit current, while the open-circuit voltage remains the same. Therefore the efficiency improvement is attributed to more light coupled into the cells. This omnidirectional surface texture offers an attractive solution for antireflection in both polycrystalline silicon and thin-film solar cells.
Show PACS
84.60.Jt, 42.79.Wc, 68.55.jm, 68.47.Pe

Direct measurements of the alpha-epsilon transition stress and kinetics for shocked iron

B. J. Jensen, G. T. Gray, III, and R. S. Hixson

J. Appl. Phys. 105, 103502 (2009) (7 pages)

Online Publication Date: 18 May 2009

Full Text: HTML | Sectioned HTML | PDF (282 kB)

Show Abstract
Iron undergoes a polymorphic phase transformation from the alpha-phase (bcc) to the epsilon-phase (hcp) when compressed to stresses exceeding 13 GPa. Because th