A blood glucose test strip-based sensing platform was developed for the quantification of virus and antibodies in human serum and saliva samples. For this study, we used SARS-CoV-2 virus and anti-SARS-CoV-2 spike RBD IgG as model analytes for virus and antibodies, respectively. Generally, the technique works by exploiting the enzymatic reaction of PO₄^3-with maltose in the presence of maltose phosphorylase to generate an equivalent amount of glucose that can subsequently be quantified with a blood glucose test strip and a mini potentiostat. For antibody detection, RBD-modified magnetic microparticles (MPs) were employed to capture the anti-RBD antibodies. For the detection of the SARS-CoV-2 virus, SARS-CoV-2 nucleocapsid protein (N) from inactivated virus samples were captured onto particles modified with anti-N antibodies. Subsequently, a magnet was utilized to isolate and purify the MPs along with the attached analytes. Alkaline phosphatase-conjugated secondary antibodies were then bound to the analytes attached to the respective MPs. Finally, through enzymatic reactions, specific amounts of PO₄^3- were generated in proportion to the analyte concentrations. The generated PO₄^3- was then reacted with maltose in the presence of maltose phosphorylase to generate an equimolar amount of glucose, which was then quantified using an off-the-shelf blood glucose test strip connected with a mini potentiostat. Our sensor exhibited a limit of detection of 0.42 ng/mL for anti-SARS-CoV-2 spike RBD antibody, which is sensitive enough to quantify typical concentrations of antibodies in COVID-19-infected or vaccinated individuals (>1 μg/mL). The limit of detection for the SARS-CoV-2 virus is 300 pfu/mL (5.4 × 10⁶ RNA copies/mL), which exceeds the performance recommended by the WHO (500 pfu/mL). This approach presents a versatile biosensing platform with the potential to detect other viruses and antibodies and use it as a point-of-care device.

Nicholas Balasuriya

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