Environmentally Safe Synthesis of Gold Nanoparticles for Antigen Detection in CLIA System.

The use of gold nanoparticles (AuNPs) has been explored in the last decades, and most recently, efforts have been made to associate their production with environmentally safe routes and biotechnological processes. The versatility of bioconjugation strategies used for AuNPs makes them a promising tool for developing alternative detection methods for traditional diagnostic assays. In this work, we present a chemiluminescent immunoassay based on AuNPs for specific and sensitive detection of SARS-CoV-2. The AuNPs were processed through a physical route, deposited on a solid substrate via magnetron sputtering, and functionalized with anti-SARS-CoV-2 antibodies. The colloidal stability of the AuNPs was monitored through UV-vis spectroscopy and transmission electron microscopy (TEM). UV-vis showed a plasmon resonance peak at ∼535 nm, consistent with the TEM results, which presented an average size of the AuNP around 40 nm. Altogether, nasopharyngeal swabs of 180 patients were tested with the antibody-AuNP bioconjugates to recognize their corresponding antigens through chemiluminescent immunoassays (CLIA). To assess the affinity and specificity of the functionalized AuNPs, comparative experiments of CLIA and classical enzyme-linked immunosorbent assay (ELISA) were conducted. CLIA results outperformed ELISA and were effective in detecting SARS-CoV-2-positive samples with a viral load exceeding 1.19 ng/mL. Analysis of the Receiver Operating Characteristic curve yielded an AUROC of 0.909 (95% CI: 0.864-0.955), indicating excellent discriminative ability, with a sensitivity of 91% and a specificity of 85%. The results provided new insights into AuNPs produced by an environmentally safe synthesis with excellent functionalization and detection capability for diagnostic applications.