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.

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 (PO43-) 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 PO43- 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 PO43- (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 × 106 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.

Orthophosphate Quantification in Water Utilizing an Enzymatic Reaction and a Commercial Glucometer Test Strip.

A sensor for the determination of orthophosphate (PO43-) concentration in water was developed that utilizes the enzymatic cleavage of maltose in the presence of PO43- to generate an equivalent amount of glucose. The glucose produced from this reaction was quantified using a commercial glucometer test strip coupled to a miniature potentiostat using amperometry. This sensing approach yielded a limit of detection of 1.45 µM (0.1 ppm) glucose/PO43-, which is lower than that of a commercial glucometer (≥600 µM glucose), and a dynamic range of 10 µM-3 mM. The selectivity of the approach to PO43- was evaluated by determining the device's response to known components in natural water samples. Finally, we showed that the approach can be used to determine PO43- in tap and river water samples.