A Study On The Electrochemical Behavior Of Biopolyelectrolyte Monolayer

Electrochemical biosensors have a wide range of application in the field of analytical chemistry due to both the high specificity of bioanalysis and simplicity, high sensitivity, fast response and low cost of electrochemical sensors. Polyelectrolyte monolayer, as one of the important methods for fabricating modified electrodes, is widely used in electrochemical research and biosensor development thanks for its ordered structure, low mass transfer resistance and fast response to chemical stimulation.In the past 20 years, researchers have systematically studied the self-assembled monolayers formed by alkanethiols with neutral backbone, and have found that ion pairs and charge property have a significant effect on the formal potential. With the application of monolayers on fabricating biosensors, more bio-polyelectrolyte such as DNA, peptide are introduced into the solid/liquid interface. Therefore, understanding the effects and modulation of the charged polyelectrolyte backbone and interfacial microenvironment on the formal potential of redox couple is fundamentally important for developing monolayer-based biosensors. A comprehensive understanding of the electrochemical behavior of redox couple at the polyelectrolyte monolayer/electrolyte interface can provide theoretical foundation for electrochemical research and biosensor development.In this work, electrochemical method was used to study the effect of Donnan potential, ion pairs effect and interfacial microenvironment on the formal potential. In addition, we develop a new potentiometric biosensors for detection of Protein Kinase.1 Donnan Potential Caused by Polyelectrolyte MonolayersIn this chapter, DNA-SH/MO-SH strands with the same sequence were self-assembled at the surface of gold electrode and ferrocene was labeled to the end of the strands as the electrochemical active group. The anodic peak potentials (Ea) of Fc-MO and Fc-DNA were recorded by cyclic voltammetry. The Donnan potential of polyelectrolyte monolayer is successfully isolated from ion pair potential by subtracting the corresponding Ea of Fc-MO by the one of Fc-DNA. Results show that ion pairs effect can affect the formal potential of redox couple, but has no impact on Donnan potential. Charge density of the monolayer and the salt concentration primarily modulate the Donnan equilibrium across the charged monolayer, but the effect of conformational change of the monolayer on Donnan potential also can’t be ignored. Based on the proposed molecular mechanism of Donnan equilibrium at the interface, a new type of potentiometric biosensor was develop for the detection of Protein Kinase A.2 Effect of polarity of interfacial microenvironment on formal potentials of redox couplesIn this chapter, ferrocene modified peptide was self-assembled at the surface of gold electrode and MCH/HT were used to passivate the electrodes to fabricate the Fc-pep-HT and Fc-pep-MCH electrodes. The effect of polarity of passivation layer on formal potential was studied using cyclic voltammetry. Results show that the increase of polarity of the passivation layer results in less polarization energy for the Fc/Fc+ redox couple during oxidation process, and thus the anodic peak potential shifts negatively. In addition, we studied the influences of the UV/Vis modulated conformational change of azobenzene on formal potential of Fc. The obtained data further confirms that the formal potential of redox couple can be affected by the polarity of passivation layer. Moreover, we observed that, after adding 1-butanol or benzyl alcohol in the electrolyte, the potential of Fc-pep-HT and Fc-pep-MCH electrode shift positively and negatively, respectively. Based on this observation, we established an interaction model between 1-butanol and the passivation layer, and the shift of formal potential is attributed to the change of the polarity of passivation layer.