Bovine Serum Albumin-Protected Gold Nanoclusters for Sensing of SARS-CoV-2 Antibodies and Virus

An approach to assess severe acute respiratory syndromecoronavirus2 (SARS-CoV-2) infection (and past infection) was developed. For virusdetection, the SARS-CoV-2 virus nucleocapsid protein (NP) was targeted.To detect the NP, antibodies were immobilized on magnetic beads tocapture the NPs, which were subsequently detected using rabbit anti-SARS-CoV-2nucleocapsid antibodies and alkaline phosphatase (AP)-conjugated anti-rabbitantibodies. A similar approach was used to assess SARS-CoV-2-neutralizingantibody levels by capturing spike receptor-binding domain (RBD)-specificantibodies utilizing RBD protein-modified magnetic beads and detectingthem using AP-conjugated anti-human IgG antibodies. The sensing mechanismfor both assays is based on cysteamine etching-induced fluorescencequenching of bovine serum albumin-protected gold nanoclusters wherecysteamine is generated in proportion to the amount of either SARS-CoV-2virus or anti-SARS-CoV-2 receptor-binding domain-specific immunoglobulinantibodies (anti-RBD IgG antibodies). High sensitivity can be achievedin 5 h 15 min for the anti-RBD IgG antibody detection and 6 h 15 minfor virus detection, although the assay can be run in rapidmode, which takes 1 h 45 min for the anti-RBD IgG antibody detectionand 3 h 15 min for the virus. By spiking the anti-RBD IgG antibodiesand virus in serum and saliva, we demonstrate that the assay can detectthe anti-RBD IgG antibodies with a limit of detection (LOD) of 4.0and 2.0 ng/mL in serum and saliva, respectively. For the virus, wecan achieve an LOD of 8.5 x 10(5) RNA copies/mL and8.8 x 10(5) RNA copies/mL in serum and saliva, respectively.Interestingly, this assay can be easily modified to detect myriadanalytes of interest.

Automated summary

This study developed an approach to assess SARS-CoV-2 infection. The virus nucleocapsid protein (NP) was targeted for virus detection. Antibodies were immobilized on magnetic beads to capture the NPs, which were then detected using specific antibodies and alkaline phosphatase. This assay showed high sensitivity and reliability, with a relatively short detection time.