Concentration dependence and cognate protein response of Aptamer-S and Aptamer-N–derivatized GFET sensor. (A) RBD concentration (0 to 200 nM)-dependent sensor response on Aptamer-S–derivatized GFET. (B) N-protein concentration (0 to 100 nM)-dependent sensor response on Aptamer-S–derivatized GFET. (Refer to SI Appendix, Fig. S6 for normalized IDS vs. VGS curves.) (C) Aptamer-S–derivatized GFET sensors were able to detect B.1.1.7 variant (N501Y), mink-related mutation (Y453F), and mutation at S2 domain (D614G) of SARS-Cov-2. Error bars of A–C were calculated from data from three different chips. (Refer to SI Appendix, Fig. S7 for normalized IDS vs. VGS curves.) (D) Response of the N- and S-aptamer–derivatized GFET sensors for S and N proteins (cognate, 100 nM concentration) of the Omicron variant (B1.1.529). P values are generated from a two-tailed Student’s t test: **P < 0.05, *P < 0.1. The error bars for D were calculated using data from two chips for each bar.