Fig. 1. (A) Absorption spectra from citrate coated gold nanoparticles, PEG coated gold nanoparticles, and anti-spike antibody attached gold nanoparticles. (B) The color of antibody attached GNPs in the presence of different amounts of COVID-19 antigen from 1 pg mL−1 to 1000 pg mL−1. (C) Selectivity of the anti-spike antibody attached gold nanoparticle-based colorimetric assay for COVID-19 antigen (5 ng mL−1). No color change was observed in the presence of 5 ng mL−1 MERS-CoV nucleoprotein antigen and 5 ng mL−1 SERS-CoV nucleoprotein antigen. (D) Absorption spectra from antibody attached GNPs in the presence of different concentrations of COVID-19 antigen.
