A novel capacitive biosensor based on electropolymerized molecularly imprinted polymer (MIP) for glutathione detection is reported. The capacitive sensor was prepared by electropolymerizing o-phenylenediamine (o-PD) on a self-assembled 2-mercaptoethane sulfonate (MES) monolayer modified gold electrode in the presence of template glutathione. 1-Dodecanethiol was used to block the defect of polymer film to improve its dielectric performance. Hydrolization procedure was selected to remove the template thoroughly for better sensitivity. The dielectric property of the sensitive layer was characterized by differential pulse voltammetry (DPV). The linear response range of the sensor for glutathione was between 0.025 and 0.30 mmol L À1 with a detection limit of 1.25 Â 10 À3 mmol L À1. Satisfactory results were obtained in the direct detection of real samples. The selectivity was evaluated by capacitance selective coefficient of glutathione and other compounds. The kinetic aspects of the recognition process were investigated by capacitive transduction. A two-step kinetic model was derived to describe the interaction between analyte and imprint sites. Fitted results were well in agreement with the corresponding experimental results.

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A novel voltammetry with a modified gold electrode for the direct determination of copper in environmental samples, without any pretreatment, is proposed in this paper. A porous disorganized monolayer was formed on the surface of the gold electrode by the self-assembly of mercaptoacetic acid (MAA), which could selectively permeate small molecules. Subtractive square wave anodic stripping voltammetry (SASV) was applied to determine copper, in which the underpotential deposition (UPD) of copper was used as the deposition step. The linear range was from 8 × 10 -7 to 1 × 10 -5 mol l -1 by the modified electrode in the presence of human serum albumin, and the determination was not interfered with common metal ions. Copper in a real environmental sample was successfully detected.

Electrochemical impendence spectroscopy (EIS), cyclic voltammetry (CV) and differential pulse voltammetry (DPV) were performed to investigate the barrier properties and electron transfer of derivatized thiol self-assembled monolayers (SAMs) on gold in the presence of surfactants. The thiol derivatives used included 2-mercaptoethanesulfonic acid (MES), 2-mercaptoacetic acid (MAA), and N-acetyl-L-cysteine (NAC). A simple equivalent circuit was derived to fit the impedance spectra very well. The negative redox probe [Fe(CN)6] 3-/4-was selected to indicate the electron-transfer efficiency on the interface of the studied electrodes. It was found that by changing the surface structure of SAMs, different surfactants could regulate the barrier properties and electron-transfer efficiency in different ways. A positively charged surfactant lowered the electrostatic repulsion between the negative redox probe and negatively charged surface groups of a monolayer, while enhancing the reversibility of electron transfer by virtue of increasing the redox probe concentration within the electric double-layer region. A neutral surfactant showed no significant effect, while a negative surfactant hindered the access and reaction of redox probe by electrostatic repulsion of same-sign charges.

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