Fabrication And Application Of Self-assembled Monolayers On Gold Electrodes

Self-assembled monolayer films (SAMs) has grown into an extremely development as a kind of new-type organic membrane in the past 20 years, and it has made great progress of SAMs's fabrication and characterization. SAMs are formed by spontaneous adsorption of self-assembling molecules from either a single component or a mixture on a solid substrate. Though many self-assembly systems have been invested, monolayer of thiolates gold electrodes are probably the most studied SAMs to date. At present, various applications have been reported on modified gold electrode, but most reports studied the properties of SAMs on gold electrode for analytical purposes. The reaction mechanism of protons transfer, thermodynamic and kinetic analysis of the interaction has never been reported. In this work, we attempt to describe the fabrication, mechanism and application of SAMs on gold electrode.1. Determination of the surface isoelectric point of self-assembled modified gold electrode.Interfacial proton transfer studies are crucial to understand and control acid/base properties of surface confined molecules and are essential to applications including fundamental studies of interfacial phenomena. Thiols of short alkyl chain length and different terminal group (COOH and NH₂) were self-assembled on gold electrodes. Fe(CN)₆^3-/4- is used to probe the variation of the self assembled monolayer terminal group charge with the change in solution pH by the differential pulse voltammetry (DPV) titration method. The surface pK values for the amino group of cysteamine and the carboxyl groups of meso-2, 3-dimercaptosuccinic acid and 3,3'-dithiodipropionic acid were reported. In particular, the surface isoelectric point of L-cysteine and penicillamine were studied at different pH by differential pulse voltammetry titration. And we are interested in comparing analysis titration curves of carboxyl-terminated, amino-terminated and both carboxyl-terminated and amino-terminated self-assembled films.2. Electrochemical behavior of epinephrine at different self-assembled monolayer on gold electrode A self-assembled monolayer of 3,3'-dithiodipropionic acid (DTDPA) and a mixed self-assembled monolayer (SAM) of meso-2, 3-dimercaptosuccinic acid (DMSA) and penicillamine (PCA) were prepared on gold electrode. The mixed SAM of DMSA and PCA, which the volume ratio of DMSA : PCA was 2:1, showed an obvious electrochemical activity for the oxidation of epinephrine (EP). The self-assembled electrode of DTDPA has also an obvious of electrochemical activity for the oxidation of epinephrine. Under the optimum conditions, the possible reaction mechanism has been discussed and parameters also have been determined. Both modified gold electrodes have a high stability and can be applied to the determination in practical samples with simplicity, rapidness and accurate results.3. Thermodynamic and kinetic analysis of the interaction between hepatitis B surface antibody and antigen on SAMs electrodeHepatitis B surface antibody (HBsAb) was immobilized to the surface of a gold electrode modified with colloidal gold as matrices to detect hepatitis B surface antigen (HBsAg). Differential pulse voltammetry (DPV) method and electrochemical impedance spectroscopy (EIS) method were used for the investigation of the specific interaction between the immobilized HBsAb and HBsAg in solution, which was followed as a change of peak current in DPV or electron-transfer resistance of EIS with time. With the modified gold electrode, the differences in affinity of HBsAb with HBsAg at the temperatures of 37℃and 40℃were easily distinguished and the kinetic rate constants (k_ass and k_diss) and kinetic affinity constant K were determined from the curves of current versus time and resistance versus time. The obtained quantitative information on the kinetics of binding is vital to understand the immune pathology of hepatitis B on a molecular level.