Femtomolar-level detection of SARS-CoV-2 spike proteins using toroidal plasmonic metasensors

TL;DR

This study introduces a novel toroidal plasmonic metasensor capable of detecting SARS-CoV-2 spike proteins at femtomolar levels, offering a highly sensitive diagnostic tool for COVID-19 using terahertz frequency modes.

Contribution

The paper presents the design and fabrication of a miniaturized toroidal metasurface immunosensor that achieves ultra-sensitive detection of SARS-CoV-2 spike proteins at femtomolar concentrations.

Findings

Detects spike proteins at ~4.2 fmol LoD

Uses toroidal dipole modes in terahertz frequencies

Achieves ultranarrow resonance lineshapes

Abstract

Effective and efficient management of human betacoronavirus severe acute respiratory syndrome (SARS)-CoV-2 infection i.e., COVID-19 pandemic, required sensitive sensors with short sample-to-result durations for performing diagnostics. In this direction, one of appropriate alternative approach to detect SARS-CoV-2 at low level (fmol) is exploring plasmonic metasensor technology for COVID-19 diagnostics, which offers exquisite opportunities in advanced healthcare programs, and modern clinical diagnostics. The intrinsic merits of plasmonic metasensors stem from their capability to squeeze electromagnetic fields, simultaneously in frequency, time, and space. However, the detection of low-molecular weight biomolecules at low densities is a typical drawback of conventional metasensors that has recently been addressed using toroidal metasurface technology. This research reports fabrication of a miniaturized plasmonic immunosensor based on toroidal electrodynamics concept that can sustain robustly confined plasmonic modes with ultranarrow lineshapes in the terahertz (THz) frequencies. By exciting toroidal dipole mode using our quasi-infinite metasurface and a judiciously optimized protocol based on functionalized gold nanoparticles (NPs) conjugated with the specific monoclonal antibody of SARS-CoV-2 onto the metasurface, the resonance shifts for diverse concentrations of the spike protein is monitored. Possessing molecular weight around ~76 kDa allowed us to detect the presence of spike protein with significantly low LoD ~4.2 fmol.