Thiolate monolayers formed on different amalgam electrodes. Part II: Properties and application

Properties of thiol monolayers were investigated at electrodes of solid amalgams of silver, copper, bismuth, cadmium (MeSAE) and at hanging mercury drop electrode (HMDE). The concentration dependences of studied thiol (HS(CH2)10COOH; MUA) at HMDE, m-AgASE, MF-AgSAE and m-CuSAE were similar for all electrodes and the Langmuir equation was used for evaluation of obtained results. Calculated values of ΔGads were very close for all electrodes. The lowest saturated surface coverage was observed for HMDE (8.5 × 10−10 mol cm−2) and the highest one for MF-AgSAE (9.8 × 10−10 mol cm−2). Nonlinear dependences of the peak currents on the scan rate show that lateral interactions exist among adsorbed molecules. When the scan rate is increased, the negative value of the peak potential increases proportionally with the natural logarithm of the scan rate. The potential of the desorption peak is almost unchanged if the thiol surface coverage (Θ) is 50% or lower. At higher values of Θ the adsorbate molecules attract each other and the peak potential at all electrodes shifts to more negative values. The dependence of the peak width at half height (W1/2) on Θ shows that the desorption peak is wide if the surface coverage is approximately 50% or lower. From Θ ≈ 80% up to full coverage of the electrode surfaces the peak width practically does not change and W1/2 ≈ 9–12 mV. Statistical results of repeated preparations of thiol monolayer and its subsequent desorption confirm that stationary amalgam electrodes are a suitable instrument to study the electrochemical properties of thiol films. Biosensor based on the use of strong and selective (strept)avidin–biotin interaction has been prepared for the first time at silver amalgam electrodes. Avidin or streptavidin are bound to the MUA monolayer by amide bond and therefore such biosensor is very stable.