(Color online) Fabrication process for nanogap IDE arrays using e-beam evaporation at a given tilted angle, combined with dry etching of the SiO2 substrate. Conventional photolithography was used to define the microscaled IDE arrays with 3-μm width and spacing. Then, e-beam evaporation with at a given tilted angle was carried out to form the nanogap IDE arrays.
(Color online) (a) Optical microscopy image of the prepatterned IDE arrays with 3-μm width and spacing. (b) Optical microscopy (left) image of the realized structures of the nanogap IDE arrays and scanning electron microscopy image (right) of a cross-section along the white line (A–A′) in the left figure clearly showing the 400-nm spacing between electrodes.
(Color online) (a) Scanning electron microscopy images showing electrode gap spacings of 400 nm (far left), 200 nm, and 100 nm, corresponding to tilted angles of 75°, 60°, and 45°, respectively. (b) The tilted angle dependence of the gap size. The inset reveals that higher tilted angles provided larger shadow effects.
(Color online) (a) Impedance spectra as a function of frequency, showing the difference in impedance at low frequencies between the 3-μm and 400-nm gap IDE arrays. The inset shows the experimental set-up of the impedance spectroscopy with the IDE arrays and the HP4192a. (b)Equivalent circuit model consisting of the dielectric capacitance (C di) of the solution, the resistance (R s) of the bulk solution, and the constant phase element (Z CPE).
(Color online) Phase shifts in accordance with the impedance spectra. The peak position of (a) 3-μm IDE arrays occurs at a lower frequency (∼6kHz) than that (∼15 kHz) of the (b) 400-nm gap IDE arrays, indicating that the resistance of the measured solution is higher in the case of 3-μm IDE arrays.
(Color online) (a) E-field distribution surrounding 400-nm gap IDE arrays through the simulation using FlexPDE software based on finite element method. (b) Magnitude of E-field along the white line (1→2) in (a)according to varying gap spacing.
(Color online) Numerical simulation results: E-field distribution in the vicinity of electrodes showing a better sensitivity of (a) the nanogap IDE arrays than (b) the 3-μm IDE arrays. It is assumed that the biomaterials with 50-nm thickness are located between the electrodes. The plots show the magnitude of E-field along the white line (1→2) in the contour figures. For nanogap IDE arrays, the E-field behavior between electrodes with Biomaterials were changed significantly. The color scale corresponds to electrical field (V/cm), and the actual electrode height of 300 nm is only small in the E-field vs height plots.
Estimated impedance parameters fitted to the equivalent circuit model.
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