Development of a simple gelatin-based sensing platform for the sensitive label-free impedimetric detection of SARS-CoV-2

The persistent nature of the SARS-CoV-2 virus, characterized by its large-scale periodical recurrence and high infectivity, has imposed an increasing demand for rapid and frequent tests. This paper presents a simple, disposable, sensitive, and selective label-free sensor for impedimetric detection of the virus Spike S1 protein. We modified a screen-printed carbon electrode with gelatin as the biocompatible support to deposit a protein A layer, acting as the structure-directing agent for subsequent site-induced binding of antibodies. We thoroughly investigated the main design factors, such as gelatin deposition, protein A and antibody concentrations, incubation time, BSA blocking time, followed by the analytical performance studies using the Spike S1 protein in phosphate-buffered saline (PBS) and artificial nasopharyngeal fluid (ANF). The immunosensor exhibited an excellent linear impedimetric response for Spike S1 in the clinically-relevant range of 0.001 - 10 mu g mL(-1) (13 pM - 130 nM), along with very low limits of detection of 169 pg mL(-1) (2.2 pM) in PBS and 90 pg mL(-1) (1.2 pM) in ANF. Together with favorable stability, repeatability, and selectivity, the newly developed immunosensor can be designated for its point-of-need application.