For the purpose to handle the ongoing pandemic of the coronavirus disease 2019 (COVID-19) rapid, specific, sensitive, and simple diagnosis methods are required. The causative agent of the COVID-19 is severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), whose RNA, structural proteins, or antibodies against it can act as target biomolecules for the detection of infection in a patient sample. Biosensors are widely used for the identifications of informational biomolecules, namely, nucleic acids [1] and proteins. The latter type includes immunosensors, which work principal is the detection of antigen-antibody coupling [2]. One of the most common types of immunosensors are based on electrochemistry, because of their affordability and simplicity without loss in accuracy and sensitivity.
Our study aimed to investigate the possibility to develop a novel method for viral disease diagnosis employing a common electrochemical technique. In our work, we used electrochemical impedance spectroscopy (EIS) as a powerful tool for observing the interaction between an immobilized virus antigen and antiviral antibodies at the modified working electrode surface. Immobilization of the antigen and formation of the antigen-antibody complex affected ion diffusion and electrical capacitance, thus influencing on electrochemical impedance of electrodes [3]. To immobilize the virus antigen on the working surface a self-assembled monolayer (SAM) was used, as an effective reusable tool for stable covalent binding of biomolecules to the different solid surfaces [4]. SAM modification was applied to the working gold electrode being part of an electrochemical cell that also included the platinum counter electrode and the reference [Ag/AgCl/KClsat] electrode.
Our experiments showed correspondences between impedimetric signals and stepwise modifications of electrode surface. We achieved a reproducible trend of significant increasing electrical impedance, i.e. electron-transfer resistance, on the key stage of antibody coupling. That fact indicates an increase in the layer thickness on the working surface and thereby testifies to the registered interaction. Hence, our outcome gives us the reason to suggest EIS-based immunosensor as an effective, rapid, easy to use, and to interpret detection tool. It is also worth noting that our experiment will serve as the basis for our further research in the field of electrochemical biosensors for the diagnosis of viral diseases in particular COVID-19.