Effect of poly-L-lysine for graphene FET biosensor in acetate buffer for highly sensitive detection of SARS-CoV-2

Abstract To increase the sensitivity of the graphene Field effect transistor (GFET) for viral detection, an acetate buffer at pH 4 was used instead of the conventional phosphate-buffer saline (PBS) at pH 7. We hypothesize that SARS-CoV-2 carries more positive charges in the acetate buffer, as its pH is further from the isoelectric point of SARS-CoV-2 (pI 5.2–6.0) compared to that of PBS. Additionally, GFET measurement results with and without poly-L-lysine (PLL) modification were compared. The dependence of sensitivity on the surface charge of graphene was estimated by solving the Poisson–Boltzmann equation, and the effect of PLL modification on this dependence was discussed.