Study On The Theory And Analytical Application Of Sinusoidal Voltammetry Phase Sensitive Detection And Time Domain Electrochemical Impedance Spectroscopy

This paper focus the study on the sinusoidal voltammetry phase selective detection andtime-domain electrochemical impedance spectroscopy based on the potential with indicialfunction. Both of these methods relate to the fast Fourier transform and the spectral harmonicanalysis techniques; the time-domain current signal was conversed to the frequency domainfor analysis.We provided an attractive solution to this problem, using phase angle instead of potentialas the basis of selectivity. Specifically, the electrochemical system was perturbed with alarge-amplitude sinusoidal potential signal and the responsive current signal was subsequentlyanalyzed in the frequency domain. Direct insight was put to the nature of “fingerprint” phaseangle of different redox compounds in Fourier transformed sinusoidal voltammetry using amodel system of two ferrocene derivatives with similar electrochemical properties. With dcbias potential as the only independent variable, the phase angle rapidly changes about180°atthe potential of current transition points which was well recognized to be associated with thehalf-wave potential. Thus, subtle difference of half-wave potential results in large phasedifference, even up to hundred degrees. Therefore the essential cause to the “fingerprint”phase angle is originated from the subtle difference of half-wave potential of molecules withsimilar electrochemical properties and low resolution in traditional dc voltammetry. Theselective detection can be realized by quantifying the amplitude of certain harmonic elementat the characteristic “fingerprint” phase angle of each redox couple; and their phase angledifference can be regulated to be close to90°to eliminate interferences and optimize theselective detection, which cannot be realized by traditional dc voltammetry.We also introduced a novel time-domain electrochemical impedance measurement basedon the stepped potential technique (SIP-EIS). The response current was Fourier transformedfast to obtain the impedance spectrum. Based on the predecessors’ work, this study optimizedsome aspects of STP-EIS on signal acquisition and smooth; and on the impedancespectroscopy measurements with dynamic impedance range greater than three orders ofmagnitude. We selected the procalcitonin (PCT) and its antibody as actual research system,which was with very less research in electrochemical immunoassay field. Twoelectrochemical immunoassay sensors with different magnitudes of dynamic range were built,and we found that the results of time-domain EIS test were consistent with the conventionalfrequency-domain EIS. This method greatly shorted the test time. It’s not only verified thefeasibility of the proposed the time-domain STP-EIS with improvements, but also provides the new method utilized electrochemical immunoassay to detect PCT.