Plasmonic Fiberoptic Absorbance Biosensor (P-FAB) for Rapid Detection of SARS-CoV-2 Nucleocapsid Protein.

SARS-CoV-2 nucleocapsid protein-based COVID-19 diagnosis is a promising alternative to the high-priced, time-consuming, and labor-intensive RT-PCR tests. Here, we developed a rapid, dip-type, wash-free plasmonic fiber optic absorbance biosensor (P-FAB) strategy for the point-of-care detection of SARS-CoV-2 N-protein, expressed abundantly during the infection. P-FAB involves a sandwich assay with plasmonic labels on the surface of a U-bent fiber optic sensor probe with a high evanescent wave absorbance (EWA) sensitivity. The SARS-CoV-2 N-protein is quantified in terms of the change in the intensity of the light propagating through the U-bent sensor probe coupled to a green LED and a photodetector. Firstly, the optical fiber material (silica vs. polymeric optical fiber), was evaluated to realize a sensitive sensor platform. The optimal size of AuNP labels (20, 40, and 60 nm) to achieve high sensitivity and a lower limit of detection (LoD) was investigated. Following the P-FAB strategy, fused silica/glass optical fiber (GOF) U-bent senor probe and citrate-capped AuNP labels (size ~40 nm) gave rise to an LoD down to ~2.5 ng/mL within 10 mins of read-out time. Further, studies on development and validation of a point of care (PoC) read-out device, and preclinical studies are in progress.