Study Of The Piezoelectric Quartz Crystal Sensing Technique And Infrared Reflection Spectroelectrochemisty

Piezoelectric quartz crystal (PQC) sensor can sensitively detect the changes in electrode mass loading and film viscoelasticity as well as solution viscosity, density, conductivity, and dielectric constant in chemical/biological reactions and processes. Infrared spectroelectrochemistry can characterize an electrochemical process at the molecular level by acquiring real time information about molecular structure of related species.The conventional combination of piezoelectric quartz crystal oscillator with electrochemistry technique generally only provides piezoelectric information of oscillation frequency in electrochemical processes. Piezoelectric quartz crystal impedance (PQCI) technique is capable of providing multidimensional piezoelectric information of the investigated system. It is expected that the novel combination of PQCI with electrochemical and/or infrared spectroelectrochemical technique(s) can acquire much more abundant information about the investigated system.In this dissertation, two combination techniques have been established, namely, PQCI in combination with electrochemistry and further with infrared spectroscopy, which have been used to study protein adsorption onto solid surfaces, the interaction between protein and tannine, generation and deposition of nano colloid, electrochemical oxidation of pyridoxol (PN), and electrodeposition and electrochemical properties of poly(o-aminophenol), with the help of fluorescence spectroscopy and scanning electric microscopy (SEM). The main work is summarized as follows:1) We established the combination technique of PQCI with electrochemical impedance. The adsorption of proteins on bare gold, and polyaniline or thiols-modified Au electrodes, and the interaction between proteins and small molecules were investigated in situ by using quartz crystal impedance analysis in combination with electrochemical impedance technique. Multidimensional parameters, such as resonance frequency, motional resistance, motional inductance, motional capacitance, the value of half peak width of theelectroacoustic conductance spectrum (δf_G1/2 as well as the electrical double-layer capacitance were obtained. The main results are as follows: (1) The dynamics of the adsorption process of lysozyme onto bare and thiols-modified Au electrodes were monitored and studied. It is found that the adsorbed amount of lysozyme is strongly dependent on the surface hydrophilicity and electrode potential. The maximal adsorption amount was observed on the n-dodecanethiol-modified Au electrode, while the adsorption was favorable at negative electrode potentials. (2) A new electrode-modification method capable of modulating the electrode-surface hydrophilicity via ion-doping protocol was put forward. A series of modified electrodes with different hydrophilicity was thus obtained. The maximal adsorption amounts of bovine serum albumin (BSA) and fibrinogen were obtained on the polyaniline film deposited in an aniline solution containing sodium dodecyl sulfate (SDS) at its critical micelle concentration (CMC). (3) The interaction between tannin and BSA was studied by using the combining technique of PQCI and electrochemical impedance spectrum (EIS) and fluorescence spectrophotometry. In diluted tannin solutions, the molar ratio of tannin binding to BSA was 2:1. While in concentrated tannin solutions, induced precipitation of BSA was observed.2) Piezoelectric quartz crystal impedance technique was introduced into the sol-gel research field to monitor in situ the processes of generation and precipitation of colloids. The main results are as follows: (1) Generation and precipitation of the ferric hydroxide sol in Fe(NC>3)3 aqueous solutions at 90°C were monitored in situ. Three basic steps, sol generation and simultaneous adsorption, adsorption equilibrium, and precipitation of ferric hydroxide sol, were identified and discussed respectively. The critical concentration of Na2SO.? for sol coagulation was measured. (2) Through hydrolysis of tetraethyl orthosilicate in alcohol solution containing 6-15 mol L"1 of water and 0.2 - 2.0 mol L"1 of ammonia, generation and precipitation process of sub-micro-sized monodispersed silica particles were monitored. It is found that the effect of ammonia concentration on the hydrolytic reaction was larger than that of water, and that the reaction can be analyzed by quasi first-order reaction kinetics. The particle's distribution density and its mass coverage were calculated from the data obtained by scanning electron microscope (SEM)and piezoelectric impedance.3) A new combined technique, i.e. in situ quartz crystal impedance in combination with infrared spectroscopy and electrochemistry, was established in this work. The electrochemical oxidation process of pyridoxol (PN) was investigated with the combined technique of piezoelectric quartz crystal impedance and electrochemistry and the technique of infrared spectroelectrochemistry. The electrodeposition and the electrochemical redox process of poly-o-aminophenol in acidic solutions were investigated with the technique of in situ quartz crystal impedance combining with infrared spectroscopy and electrochemistry, and it was used as an exemplum for the application of the novel combined technique. The main results are as follows: (1) The major tautomeric equilibriums of PN molecules at various pH were studied. A lactone form of PN as an intermediate of PN oxidation and adsorption on gold surface was detected. The oxidation mechanism of PN in alkaline solution was proposed. (2) Piezoelectric infrared spectroelectrochemistry was successfully used to investigate the electrochemical deposition and electrochemical properties of poly-o-aminophenol. The mass changes of polymeric film, ion-doping behaviors, and information about the chemical structural changes of the film structure were obtained and discussed. The results indicated that this new method could be widely applied to the investigations on electrode-surface-relevant processes.