A Rapid Colorimetric Method to Investigate SARS-CoV-2 by Using Gold Nanoparticles Capped with O-Hydroxybenzoic Acid

A rapid, sensitive, and stable colorimetric sensor applied on gold nanoparticles (AuNPs) has been established. AuNPs were synthesized by o-hydroxybenzoic acid; then, the surface was modified by N-ethyl-N’-(3-dimethyl aminopropyl) carbodiimide hydrochloride (EDC)/N-Hydroxysuccinimide (EDC/NHS) and bioconjugated with SARS-CoV-2 (SC-2) antibody (AuNPs-mAb). O-hydroxybenzoic acid consists of a carboxyl group and thus can reduce one step of the reaction in bioconjugation with SC-2 antibody. AuNPs-mAb were proven to detect the SC-2 antigen as indicated by the decrease of the UV-Vis absorbance and a visible color difference from purplish-red to colorless AuNPs. Detection limit (LoD) and quantification limit (LoQ) were 16.03 and 53.42 ng/mL, respectively, with a linear concentration range of 75-250 ng/mL. SC-2 can be detected with the naked eye using AuNPs-mAb in less than 5-minute incubation time (rapid), and AuNPs-SC-2 are stable for four weeks at 4 °C. The comparative study for AuNPs-mAb performance to detect the SC-2 antigen has been done with an enzyme-linked immunosorbent assay (ELISA). The data show that AuNPs have higher sensitivity than the conventional ELISA method in the same concentration range. Because the detection system based on AuNPs capped with o-hydroxybenzoic acid is rapid, stable, and practical, this method can be an alternative to early screening for COVID-19.