Chi 440c

Chloroauric acid trihydrate (HAuCl₄, 4~50% Au basis), iron (II, III) oxide (MBs,100–200 nm, 5 mg mL⁻¹), chloroplatinic acid (H₂PtCl₆, 99.9%), single-layer graphene oxide dispersion (2 mg mL⁻¹, dispersion in H₂O), acetylthiocholine iodide (ACH), acetylcholinesterase (AChE, 200 U g⁻¹), and choline oxidase (CHOx, 8–20 U mg⁻¹) were purchased from Shanghai Macklin Biochemical Co., Ltd. (Shanghai, China). Trisodium citrate dihydrate (C₆H₅Na₃O₇·2H₂O), ethylenediaminetetraacetic acid disodium salt (C₁₀H₁₄N₂Na₂O₈), citric acid monohydrate (C₆H₁₀O₈), glycerol (C₃H₈O₃), and dimethyl sulfoxide (DMSO, C₂H₆OS) were bought from Xilong Scientific Co., Ltd. (Guangzhou, China).
A 5500 UV-vis spectrometer (Shanghai Yuanxi Instrument Co., Ltd., Shanghai, China) was used to obtain UV-vis absorption spectra. All electrochemical measurements were performed on a CHI 440C (CH Instruments, Inc., Dellas, TX, USA) electrochemical workstation with a three-electrode system (a glassy carbon electrode, a platinum wire, and Ag/AgCl electrode were used as working, counter, and reference electrode, respectively).

The cyclic voltammetry was performed with a computer-controlled electrochemical analyzer (CHI 440 C, CH Instruments), using three-electrode configuration; Protein nanowires (~170 nm) or SiO₂ dielectric (~160 nm) were coated on Au electrodes (size ~25 mm²) as the working electrodes. A platinum wire and Ag/AgCl electrode were used as the counter electrode and reference electrode, respectively. A 0.10 M KNO₃ solution (with Ag⁺ 5 mM) was used as the electrolyte for the electrochemical measurements.