(a) Chip design and construction. The electrode patterns of the bottom layer were fabricated on a thin cover slip slide and the electrode pattern of the top layer was fabricated on a treated glass slide. A roughened metal shelter was designed in front of the trapping electrode of the top layer that not only reduces the fluorescence noise but also enhances Raman signal. (b) Finished chip.
Configuration of the setup. The samples were injected into the microfluidic chip using a syringe pump. After the separation procedure, the bacteria were trapped by negative DEP force and aggregated into the roughened metal shelter for SERS detection.
(a) Microscopy image and (b) AFM image of two types of roughened Au surface. (c) RS-1 surface demonstrated flat peaks with a peak-to-valley roughness of 80–100 nm. RS-2 surface demonstrated sharper peaks with peak-to-valley roughness of 60–80 nm.
(a) The Raman spectra of S. aureus detected by different roughened electrode surfaces. The purple curve, blue curve, and red curve were obtained from the RS-1, the RS-2, and the smooth Au surface, respectively. (b) The measurement results of S. aureus [curve (a)] and P. aeruginosa [curve (b)] show distinct SERS spectra that are promising for fingerprint discrimination.
Results of guiding, sorting, and concentrating. (a) Blood cells and bacteria were guided to the sorting electrode by nDEP and laminar flow. (b) Blood cells were repelled to the upper subchannel while bacteria penetrated the paired electrode that flowed to the lower subchannel. Blood cells (c) and bacteria (d) were concentrated at their specific locations after the guiding and sorting steps.
(a) The Raman spectra of S. aureus detected on the integrated chip. Curves (a), (b), and (c) were obtained on a 3D chip with a roughened Au shelter surface (RS-2), with smooth Au shelter, and without an Au shelter, respectively. (b) The SERS signatures of S. aureus, RBC, and RBCs/bacteria mixture .
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