2.2. Apparatus

Morphological characterization of stainless-steel substrate, Au modified electrode, and β-CD-Au electrode were recorded using a field-emission scanning electron microscopy (FESEM, Hitachi S-4800, Japan) and atomic force microscope (AFM, SPI-3800N, Japan). The elemental content was obtained by X-ray photoelectron spectroscopy (XPS, PHI 5000c, PerkinElmer Instruments, Waltham, MA, USA). A three-electrode system was used in the experiment, including a working electrode, Ag/AgCl reference electrode, and Pt counter electrode. The applied potentials in all the measurements were vs. the Ag/AgCl reference electrode. The electrochemical impedance spectroscopy (EIS) was carried out with CHI660C electrochemical workstation (Chenhua, China) at 0.24 V, and its AC disturbance voltage was in the frequency range between 0.1 and 10⁵ Hz.