Since emerging in China in December 2019, COVID-19 has spread globally, wreaked havoc for public health and economies worldwide and, given the high infectivity and unexpectedly rapid spread of the virus responsible—that is, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)—urged the World Health Organization to declare it a pandemic. In response, reducing the virus’s adverse effects requires developing methods of early diagnosis that are reliable, are inexpensive and offer rapid response. As demonstrated in this article, the colorimetric and electrochemical detection of SARS-CoV-2 spike antigens with gold nanoparticle-based biosensors may be one such method. In the presence of the SARS-CoV-2 antigen, gold nanoparticles aggregated rapidly and irreversibly due to antibody–antigen interaction and consequently changed in colour from red to purple, as easily observable with the naked eye or UV-Vis spectrometry by way of spectral redshifting with a detection limit of 48 ng/mL. Moreover, electrochemical detection was achieved by dropping developed probe solution onto the commercially available and disposable screen-printed gold electrode without requiring any electrode preparation and modification. The method identified 1 pg/mL of the SARS-CoV-2 spike antigen and showed a linear response to the SARS-CoV-2 spike antigen ranging from 1 pg/mL to 10 ng/mL. Both methods were highly specific to detecting the SARS-CoV-2 antigen but not other antigens, including influenza A (i.e. H1N1), MERS-CoV and Streptococcus pneumoniae , even at high concentrations.

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