SARS-CoV-2 detection enabled by a portable and label-free photoelectrochemical genosensor using graphitic carbon nitride and gold nanoparticles

Fast, sensitive, simple, and cheap sensors are highly desirable to be applied in the health system because they improve point-of-care diagnostics, which can reduce the number of cases of infection or even deaths. In this context, here we report the development of a label-free genosensor using a screen-printed electrode modified with 2D-carbonylated graphitic carbon nitride (c-g-C₃N₄), poly(diallyldimethylammonium) chloride (PDDA), and glutathione-protected gold nanoparticles (GSH-AuNPs) for photoelectrochemical (PEC) detection of SARS-CoV-2. We also made use of Arduino and 3D printing to miniaturize the sensor device. The electrode surface was characterized by AFM and SEM techniques, and the gold nanoparticles by UV-Vis spectrophotometry. For SARS-CoV-2 detection, capture probe DNA was immobilized on the electrode surface. The hybridization of the final genosensor was tested with a synthetic single-strand DNA target and with natural saliva samples using the photoelectrochemistry method. The device presented a linear range from 1 to 10,000 fmol L^-1 and a limit of detection of 2.2 and 3.4 fmol L^-1 using cpDNA 1A and 3A respectively. The sensibility and accuracy found for the genosensor using cpDNA 1A using biological samples were 93.3 and 80% respectively, indicating the potential of the label-free and portable genosensor to detect SARS-CoV-2 RNA in saliva samples.