Detection of the SARS-CoV-2 S protein using AuNPs assisted differential-phase surface plasmon resonance biosensor

Developing an efficient and sensitive method for detecting the coronavirus disease (COVID-19) is crucial. In this study, a phase-dependent SPR biosensor has been developed to detect the SARS-CoV-2 S protein with high sensitivity. The phase shifts of the SPR spectral interferogram are extracted using the windowed Fourier transform (WFT) method. The summation of the phase shifts of the prominent frequency, which make up the SPR spectral interferogram, is used as a numerical index to reflect the "negative" or "positive" results. The SARS-CoV2 S protein antibody is modified onto an Au film, which serves as a sensing surface when detecting the SARSCoV-2 S protein. The SARS-CoV-2 S protein antibody functionalized Au nanoparticles are used to form a (antiS@AuNPs)-(SARS-CoV-2 S protein)-(Au film) sandwich structure, which reduces the SPR detection limitation to 1 ag/mL. An external laser is then used to induce the localized surface plasmon resonance (LSPR) between the AuNPs and the Au film in the sandwich structure, enhancing the detecting sensitivity by 357 %. This study provides a label-free method for detecting the SARS-CoV-2 S protein with low concentrations, indicating its potential in detecting the SARS-CoV-2 virus and viral disease diagnosis.