Electrochemical sensing of SARS-CoV-2 amplicons with PCB electrodes

Abstract

We present a low-cost electrochemical DNA biosensor based on printed circuit board (PCB) electrodes for wastewater monitoring using portable PCR instruments, such as miniPCR®, without the requirement for qPCR reagents. PCB electrodes are attractive candidates for low-cost and sensitive DNA biosensors of relevance in a pandemic such as COVID-19, and facilitate the opportunity to map disease spread in Low-Middle Income Countries (LMICs) through monitoring of environmental samples such as wastewater. The biosensor reported in this work is capable of detecting PCR amplicons through the intercalation of methylene blue (MB) with DNA, which increases the voltammogram peak current at the redox potential of MB. We describe how these changes are likely to result from the adsorption of MB-DNA complex on the electrode surface. The electrodes are reusable, easy to clean, do not undergo any surface modification and represent a cost-effective solution with long shelf-life. We also explore the impact that MB concentration and DNA length have upon our biosensor performance and provide insights useful to other investigators in the field. The sensor reported here is capable of detecting SARS-CoV-2 nucleocapsid gene amplicons at concentrations as low as 10 pg/μl (approximately 1.7 fM) and can detect nucleotides amplified after 10 PCR cycles. Furthermore, using the PCB electrode and approaches described here, SARS-CoV-2 amplicons were detected in simulated wastewater sample, by spiking wastewater collected from a sewage treatment plant in Mumbai, India with SARS-CoV-2 RNA.