Xinkui Wang

Assessing the apparent effective thickness of alkanethiol self-assembled monolayers in different concentrations of Fe(CN)63-/Fe(CN)64- by ac impedance spectroscopy

Abstract The concept of an apparent effective thickness of a self-assembled monolayer is established and assessed with the measurements of ac impedance spectroscopy in different concentrations of Fe(CN) 6 3− /Fe(CN) 6 4− by alkanethiol self-assembled monolayers on a gold electrode. The complex-plane impedance plots for SAMs in solution of various concentrations of Fe(CN) 6 3− /Fe(CN) 6 4− exhibit arc shapes. The apparent resistance ( R 2 ), obtained from the simulation, decreased with increasing concentration of the redox couples. It is determined that the apparent effective thickness of the SAMs is lower than the length of chain of the alkanethiol. Defect sites may exist at the alkanethiol monolayers.

Electrochemical behavior of the self-assembled membrane formed by calmodulin (CaM) on a Au Substrate

Abstract A membrane of calmodulin (CaM) was successfully fabricated by the self-assembly technique on a Au substrate. The electrochemical response of the membrane was investigated systematically with cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) methods, where a redox couple of Fe(CN)63−/4− was employed as the probe. The results showed that a combination of CaM with Ca2+ could lead to a decrease of the reaction resistance (Rct). The most interesting point is that the plots, which were recorded using the above two methods for the Au electrode modified with the CaM membrane (CaM/Au), showed a regular dependence on the pH of the electrolyte studied. After serial experiments, we concluded that the results we obtained could be attributed partly to the conversion process of the spatial structure of the CaM.

Electron transfer between ferrocene-modified Au/octadecanethiol/lipid BLM electrode and redox couples in solution

Bilayers incorporated with ferrocene consisting of self-assembled octadecanethiol and lipid monolayer on gold substrates were fabricated. Its electrochemical behaviors in solutions containing different redox couples were investigated by cyclic voltammetry and ac impedance. The transmembrane electron transfer reaction across octadecanethiol self-assembled film and an adsorbed phospholipid layer mediated by ferrocene have been observed in the solution of Fe(CN)6(3-/4-). The formal potential difference between mediator in bilayer lipid membrane (BLM) and redox couple in solution has a great impact on the transmembrane electron transfer behavior. The ferrocene-modified BLM electrodes might be useful for constructing a bilayer-based electrochemical current rectifying device.

Cyclic Voltammetry Studies of Octadecanethiol Self-Assembled Monolayers in Different Concentrations of Fe(CN)63−/ Fe(CN)64−

Abstract Octadecanethiol self-assembled monolayers derivatized gold electrode in different concentrations of Fe(CN)6 3−/4− was studied by cyclic voltammetry. The cyclic voltammetric responses display a series of inverse sigmoidal curves for the SAMs in the solution of various concentration of Fe(CN)6 3−/4−. A new concept of apparent effective thickness of self-assembled monolayers is established on the base of the measurements of cyclic voltammetry. It is determined that the apparent effective thickness of the SAMs is lower than the length of chain of octadecanethiol. Defect sites may be present in the alkanethiol monolayers. The apparent effective thickness can be used to describe the quality of SAMs quantitatively.

Ferrocene Mediated Transmembrane Electron Transfer on Gold Electrode Modified by Hybrid Bilayer Membrane Consisting of Octadecanethiol and Phospholipid

Abstract Supported hybrid bilayers consisting of octadecanethiol and phospholipid incorporated with ferrocene were fabricated through self-assembling methods. Its electrochemical behaviors in solutions containing different concentrations of Fe(CN)6 3-/4− were investigated by ac impedance and cyclic voltammetry. The transmembrane electron transfer across octadecanethiol self-assembled film and an adsorbed phospholipid layer mediated by ferrocene has been observed. It is determined that the apparent heterogeneous rate constant is 2.3 × 10−8 cm·s−1.