Fig. 3.
Detection performance of SARS-CoV-2 S1 spike protein antigen. (a) Real-time variation in COVID-19 sensor with the different concentrations ranging from 1 ag/mL to 1 μg/mL. (b) The Raman spectra show a shift in the graphene G peak position with the crosslinker, SARS-CoV-2 spike S1 protein antibody, and antigen (1 ag/mL) on the sensor. (c) The fractional change in output (ΔV/Vo) with varying SARS-CoV-2 S1 spike protein concentrations over the range of 1 ag/mL – 1 μg/mL (semi-log scale). A least-square fit line to the experimental data points is also shown, which yields an average sensitivity of 0.45 × 106 ± 0.05 / (g/mL) from the slope. Error bars indicate standard deviation based on measurements of the sensors.