Detecting Covid Virus Using an MFIA Impedance Analyzer

June 14, 2023 by Meng Li

In the past few years, the spread of COVID-19 pandemic has led to a tremendous development in detecting SARS-CoV-2 (and HCoV-229E) viruses. Whereas polymerase chain reaction-based fluorescence is known to be accurate, it is time-consuming and requires sophisticated setup and expertise. On the other hand, lateral flow assay (LFA) is cheaper and easier to use, yet the result is less quantitative.

In a recent work published by a group at ETH/EMPA in Switzerland, the authors have demonstrated that electrochemical (EC) sensors combine the advantages of the aforementioned methods. The RNA of the virus is collected and transcribed into complementary DNA (cDNA), which is then filled in a microfluidic chip as an EC bioassay. An MFIA impedance analyzer helps to resolve the dynamics of the binding process of cDNA to the chip electrode.

By running electrical impedance spectroscopy, we can see in the Nyquist plot (Figure 1b), that the resistance of the virus increases from 497.69 to 581.46 kOhm after cDNA hybridization. This step identifies the characteristic frequency, enabling further time-dependent measurements where the virus probe concentration is varied. Figure 1c illustrates that a higher probe concentration results in faster binding kinetics, and a larger increase of impedance before saturation. Based on this evaluation, 2 μmol is determined as the optimal condition. Measuring the EC bioassay with an MFIA is fast, taking less than 30 min, and the result is found quantitative.

Figure 1. Impedance measurements of enzymatically enhanced EC bioassay for HCoV-229E and SARS-CoV-2 RNA detection: (a) Randles circuit model and schematic diagram of mass transport and biorecognition events on chip electrodes. (b) Nyquist plot of probe-target interaction in 2 µmol. (c) Binding kinetic curves of DNA hybridization at different probe concentrations. Adapted from Figure 2 in http://doi.org/10.1002/advs.202301222.

Acknowledgments

Many thanks to Dr. Jiang, Prof. Wang, and the rest of the team for sharing this study. Here is the fully accessible paper: Jiang, Fuze, et al. "Direct Quantitation of SARS‐CoV‐2 Virus in Urban Ambient Air via a Continuous‐Flow Electrochemical Bioassay." Advanced Science (2023): 2301222.