Label-free electrochemical impedance spectroscopy using a micro interdigitated electrode inside a PCR chip for real-time monitoring

Conventional real-time PCR using fluorescence detection requires expensive optical detection systems with fluorescence labeling. To simplify this PCR system, we proposed an electrochemical impedance spectroscopy (EIS) using an interdigitated electrode integrated inside the PCR chip. The electrode makes a direct contact with the PCR sample and does not require any labeling or immobilization pretreatment. The input AC voltage for EIS showed the lowest noise at 100 mV. Electrical impedances in a frequency domain were measured during 30 cycles in the PCR of Escherichia coli genomic DNA region (of length 180 bp, 10 ng/μl). From the analysis of EIS data, the magnitude of imaginary value steadily increased with an increase in the PCR cycles and showed the greatest change rate at 186 Hz. For comparing the quantitative performance with previous researches, the figure of merit (FM) was defined as the ratio of normalized sensitivity (NS) to the normalized root mean square error (NRMSE). The performance of the proposed EIS method is similar to that reported in other studies, and the damage of the sample monitored through electrophoresis by EIS measurement was confirmed to be negligible.