Amplification-free detection of SARS-CoV-2 using gold nanotriangles functionalized with oligonucleotides
Rafael Del Caño, Tania García‐Mendiola, Daniel García-Nieto, Raquel Álvaro, Mónica Luna, Hernán Alarcón Iniesta, Rocío Coloma, Ciro Rodríguez Diaz, Paula Milán-Rois, Milagros Castellanos, Melanie Abreu, Rafael Cantón, Juan Carlos Galán, Teresa Pineda, F. Pariente, Rodolfo Miranda, Álvaro Somoza, Encarnación Lorenzo
Abstract
Gold nanotriangles (AuNTs) functionalized with dithiolated oligonucleotides have been employed to develop an amplification-free electrochemical biosensor for SARS-CoV-2 in patient samples. Gold nanotriangles, prepared through a seed-mediated growth method and exhaustively characterized by different techniques, serve as an improved electrochemical platform and for DNA probe immobilization. Azure A is used as an electrochemical indicator of the hybridization event. The biosensor detects either single stranded DNA or RNA sequences of SARS-CoV-2 of different lengths, with a low detection limit of 22.2 fM. In addition, it allows to detect point mutations in SARS-CoV-2 genome with the aim to detect more infective SARS-CoV-2 variants such as Alpha, Beta, Gamma, Delta, and Omicron. Results obtained with the biosensor in nasopharyngeal swab samples from COVID-19 patients show the possibility to clearly discriminate between non-infected and infected patient samples as well as patient samples with different viral load. Furthermore, the results correlate well with those obtained by the gold standard technique RT-qPCR, with the advantage of avoiding the amplification process and the need of sophisticated equipment.