An analysis method to detect the presence of DNA using electrochemical impedance spectroscopy (EIS) for real-time PCR

This paper reports a technique for detecting the presence of DNA in real-time PCR using label-free electrochemical impedance spectroscopy. The change in the real and imaginary parts of the impedance with the number of PCR cycles indicates the concentration of amplified DNA. In general, the real part of the impedance tends to increase with the number of PCR cycles over most of the measurement frequency range (100 Hz–1 MHz), whereas the imaginary part of the impedance increases in the negative direction. The optimal frequency for impedance analysis is determined by the performance index (PI), as one of the figures of merit, which quantitatively indicates how monotonously the impedance changes with the PCR cycle number. The detectability of DNA in the sample is scrutinized by analyzing the impedance at the optimal frequency (3.984 kHz and 20.02 kHz for the real and imaginary parts of the impedance, respectively) obtained from the performance index. The proposed technique can be used to quantitatively analyze PCR by applying simple electrochemical impedance spectroscopy (EIS) technology so that a label-free real-time monitoring system has high potential for a portable PCR system.