Removal of Thiol-SAM on a Gold Surface for Re-Use of an Interdigitated Chain-Shaped Electrode

Abstract

The self-assembled monolayer (SAM) is the most common organic assembly utilized for the formation of the monolayers of alkane-thiolates on gold electrode, resulting in a wide range of applications for the modified SAM on gold in various research areas. This study examined the desorption of a SAM that was developed on the gold surface of an interdigitated chain-shaped electrode (the ICE, a unique electrode design, was fabricated by our group) with the goal of determining the most efficient strategy of SAM removal for the ICE to be re-used. A simple and proficient solution-based cleaning procedure was applied for the removal of a SAM on the gold surface of the ICE by using a sodium borohydride solution within short-term treatment, resulting in efficiency for the recovery of the originally electrochemical characteristic of ICE of 90.3%. The re-use of ICE after the removal process was confirmed by the successful re-deposition of a SAM onto the electrode surface, resulting in the high efficiency percentage of 90.1% for the reusability of ICE with the SAM modification. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) were used as tools to investigate the changes in the electrode interface at each stage of the SAM removal and the electrode recycling. X-ray photoelectron spectroscopy and Fourier-transform infrared spectroscopy were employed, being powerful spectrum techniques, for the characterization of the bonding structure and chemical state of the bare ICE and the modified ICE at each treatment step. Based on the comprehensive discussion of analytical chemistry from the obtained EIS and CV data in this study, we confirmed and proved the effectiveness of this promising method for the removal of a SAM from the ICE and the re-use of ICE in the field of material deposition, with the aims of saving money, improving experimental handling, and protecting the environment.

Keywords: SAM removal; electrochemical impedance spectroscopy; interdigitated chain-shaped electrode; self-assembled monolayer.

Figure 1

(a) Picture of ICE, a working area microscopic image of ICE containing several fingers, and a scanning electron microscopy (SEM) image of an Au finger of ICE. (b) Deposition of the SAM, removal of the SAM (by NaBH₄), and re-deposition of the SAM procedures for the Au surface of ICE, respectively, and the corresponding EIS results at each stage.

Figure 2

(a) EIS and (b) CV results of ICE, before and after the cleaning process.

Figure 3

(a) XPS results of the ICE, ICE/SAM, and re-ICE. (b) Deconvolution of the Au 4f spectra of ICE/SAM.

Figure 4

FT-IR results of the ICE, ICE/SAM, and re-ICE.

Figure 5

(a–c) EIS, expressed by Nyquist plots, and (d) the CV results of ICE, ICE/SAM, re-ICE, re-ICE/SAM in 1 mM K[Fe(CN)₆]^3−/4− containing 0.1 M KCl. EIS spectra included the fitting data.

Figure 6

Efficiency percentage (%) for the re-use ICE and the re-deposition SAM. Columns and bars represent the averages and standard deviations of the data (n = 3).