Study Of Potential Step Based Impedance Measurement Method And Fourier Transformed Large Amplitude Square Wave Voltammetry

This paper relates to the improvements of two types of commonly used electrochemical method - electrochemical impedance spectroscopy and square wave voltammetry. Electrochemical impedance spectroscopy has played an important role in the development of immunobiosensor. Although this method is accurate and the noise has no effect on it, the equipment is complex and expensive and the measure time is very long. Therefore, we propose a fast impedance measurement method - the potential step based impedance measurement method. Traditional square wave voltammetry is often used to determine the rate constant of surface confined redox system. Because this method requires repeated scanning, the stability of the material on the surface of the electrode will be influenced.Firstly, we introduced a new type of electrochemical impedance method. We used a potential step that can be regarded to be the integrated form of a unit pulse as the excitation signal. If the as collected current response was differentiated, what we get is the unit pulse response. The impedance spectroscopy of the system is available if the as acquired pseudo-unit pulse response is subjected to Fourier transformation.Secondly, the potential step based impedance measurement method was applied on Escherichia coli O157:H7 immunosensor. The immunosensors were tested by frequency response analyzer based impedance method and potential step based impedance measurement method respectively. Almost identical results were obtained between the Nyquist plots measured by potential step based impedance measurement method and that of the frequency response analyzer based impedance method and this new method can significantly reduce the testing time.Then, we introduced Fourier transformed square wave voltammetry. A complex signal that contains many frequencies was applied to electrochemical system. The excitation signal is the combination of large amplitude square wave potential and a linear DC potential. And then the collected current response was Fourier transformed to be spectrums that contain a large number of even harmonics components. We can obtain a critical frequency from the even harmonics spectrum that was picked-up.At last, we used traditional square wave voltammetry and Fourier transformed large amplitude square wave voltammetry to test the electron transfer rate constant of azobenzene adsorbed on mercury film electrode. Preliminary results show that this method has broad application prospects in dynamic studies of surface confined redox system. We also studied the influenced factor and uninfluenced factor in Fourier transformed large amplitude square wave voltammetry.