Abstract
We report a near-infrared surface plasmon resonance (SPR) system to achieve highly sensitive, unlabeled detection of the SARS-CoV-2 nucleocapsid protein antigen. Use of the near-infrared light in SPR makes the SPR dip of the angular spectrum sharp and causes a large change of the reflected light intensity at a fixed incident angle. The present SPR system achieves the resolution of 10−5 refractive index unit in the refractive index measurement of glycerol solution samples. Additionally, we measured the nucleocapsid protein antigen of SARS-CoV-2 down to a molar concentration of 1 fM by immobilizing its corresponding antibody on the SPR sensor surface. This demonstration indicates a high potential of the present system for highly sensitive biosensing in medical diagnostics.
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