Amplification Free Detection of SARS-CoV‑2 Using Multi-Valent Binding

• Published in: ACS sensors Vol. 7; no. 12; pp. 3692 - 3699
• Main Authors: Roychoudhury, Appan, Allen, Rosalind J., Curk, Tine, Farrell, James, McAllister, Gina, Templeton, Kate, Bachmann, Till T.
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 23.12.2022
• Subjects: COVID-19 - diagnosis; Humans; Nucleic Acid Hybridization; RNA, Viral - genetics; SARS-CoV-2 - genetics; point-of-care diagnostics; SARS-CoV-2; multi-valent binding; electrochemical impedance spectroscopy; electrochemical biosensor
• ISSN: 2379-3694; 2379-3694
• DOI: 10.1021/acssensors.2c01340

We present the development of electrochemical impedance spectroscopy (EIS)-based biosensors for sensitive detection of SARS-CoV-2 RNA using multi-valent binding. By increasing the number of probe–target binding events per target molecule, multi-valent binding is a viable strategy for improving the biosensor performance. As EIS can provide sensitive and label-free measurements of nucleic acid targets during probe–target hybridization, we used multi-valent binding to build EIS biosensors for targeting SARS-CoV-2 RNA. For developing the biosensor, we explored two different approaches including probe combinations that individually bind in a single-valent fashion and the probes that bind in a multi-valent manner on their own. While we found excellent biosensor performance using probe combinations, we also discovered unexpected signal suppression. We explained the signal suppression theoretically using inter- and intra-probe hybridizations which confirmed our experimental findings. With our best probe combination, we achieved a LOD of 182 copies/μL (303 aM) of SARS-CoV-2 RNA and used these for successful evaluation of patient samples for COVID-19 diagnostics. We were also able to show the concept of multi-valent binding with shorter probes in the second approach. Here, a 13-nt-long probe has shown the best performance during SARS-CoV-2 RNA binding. Therefore, multi-valent binding approaches using EIS have high utility for direct detection of nucleic acid targets and for point-of-care diagnostics.