Utilization of a Glucometer Test Strip and Enzymatic Reactions to Quantify Anti-SARS-CoV-2 Spike RBD IgG Antibody and SARS-CoV-2 Virus in Saliva and Serum

Abstract

A sensor capable of quantifying both anti-SARS-CoV-2 spike receptor-binding domain (RBD) antibody levels and the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus in saliva and serum was developed. This was accomplished by exploiting the enzymatic reaction of maltose and orthophosphate (PO 4 3− ) in the presence of maltose phosphorylase to generate an equivalent amount of glucose that was detected using a commercial glucometer test strip and a potentiostat. Important for this approach is the ability to generate PO 4 3− in an amount that is directly related to the concentration of the analytes. RBD-modified magnetic microparticles were used to capture anti-SARS-CoV-2 spike RBD antibodies, while particles modified with anti-SARS-CoV-2 nucleocapsid antibodies were used to capture SARS-CoV-2 nucleocapsid protein from inactivated virus samples. A magnet was used to isolate and purify the magnetic microparticles (with analyte attached), and alkaline phosphatase-conjugated secondary antibodies were bound to the analytes attached to the respective magnetic microparticles. Finally, through enzymatic reactions, specific amounts of PO 4 3− (and subsequently glucose) were generated in proportion to the analyte concentration, which was then quantified using a commercial glucometer test strip. Utilizing glucose test strips makes the sensor relatively inexpensive, with a cost per test of ∼US $7 and ∼US $12 for quantifying anti-SARS-CoV-2 spike RBD antibody and SARS-CoV-2, respectively. 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 × 10 6 RNA copies/mL), which exceeds the performance recommended by the WHO (500 pfu/ mL). In addition, the sensor exhibited good selectivity when challenged with competing analytes and could be used to quantify analytes in saliva and serum matrices with an accuracy of >94% compared to RT-qPCR.

Method for Glucose and Fructose Quantitation in Beverages Using an Off-the-Shelf Glucose Test Strip

“…The utilization of commercial glucose meters does come with limitations, particularly concerning the detection limit of glucose, which is typically around 600 μM for meters such as the Accu Chek Aviva from Roche Diabetic Care. In pursuit of enhanced sensitivity, and expanding the utility of the glucose strips, our previous research efforts have introduced methods for quantifying orthophosphate, viruses, and antibodies. , These methods involved connecting the test strip to a hand-held mini-potentiostat to allow the amperometric measurement of low current levels in the nano ampere (nA) range. The amperometric signal is diffusion-limited and follows the Cottrell equation, eq : i = ( n F A D 1 / 2 C ) / false( π t false) 1 / 2 where n is the number of electrons involved in the reaction, F is the Faraday constant, A is the electrode area, D is the diffusion coefficient of the mediator, C is the initial concentration of the analyte, and t is the measurement time.…”