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. Author manuscript; available in PMC: 2021 Nov 2.
Published in final edited form as: IEEE Trans Biomed Eng. 2020 Mar 17;67(11):3203–3210. doi: 10.1109/TBME.2020.2979475

Figure 2.

Figure 2.

Electrochemical and surface characterization of both graphene microelectrode arrays and equivalent circuit model. (a) EIS results from 1 Hz to 100 kHz of graphene microelectrode array fabricated on PET substrate along with equivalent model fitting. (b) 1 kHz impedance bar chart for sample graphene microelectrode array on PET substrate. (c) EIS results from 1 Hz to 100 kHz of graphene microelectrode array fabricated on SU-8 substrate along with equivalent model fitting. (d) 1 kHz impedance bar chart for sample graphene microelectrode array on SU-8 substrate. (e) Tapping-mode atomic force microscopy (AFM) 3-dimensional photograph of PET substrate. (f) AFM 3D image of SU-8 substrate. (g) Equivalent circuit model for graphene microelectrode arrays, regardless of substrate. Rs is the series resistance. CPE is the constant phase element representing the Helmholtz double-layer capacitance. Cq represents quantum capacitance. Rct represents the charge-transfer resistance, and Wb is a bounded Warburg element representing any diffusion processes. (h) Accelerated aging test schematic showing the graphene microelectrode arrays suspended in 87 °C PBS solution. A hotplate is used to keep the PBS constantly heated, and a thermometer is held next to the arrays in order to confirm the temperature. The beaker is enclosed by a silicone stopper in order to prevent temperature changes and evaporation.