Single-Nanoparticle Detection Using Quasi-Bound States in the Continuum Supported by Silicon Metasurfaces

Area of Science:

• Nanophotonics
• Biosensing technologies
• Metasurface optics

Background:

• Optical sensors often detect global refractive index changes.
• Detecting local refractive index changes from single molecules is challenging due to limited quality factors and large mode volumes.

Purpose of the Study:

• To demonstrate low-contrast quasi-bound states in the continuum (qBIC) metasurfaces for single-nanoparticle sensing.
• To achieve virus-sized single-nanoparticle resolution in optical sensing.

Main Methods:

• Utilized low-contrast BIC metasurfaces operating at critical coupling.
• Employed polystyrene nanoparticles (100 nm diameter) to probe sensor response.
• Analyzed resonance wavelength shifts, linewidth, and amplitude changes.

Main Results:

• Achieved an experimental quality (Q) factor of 4.5 × 10⁴ in heavy water.
• Observed step-like resonance wavelength shifts indicating individual nanoparticle binding.
• Demonstrated single-particle sensitivity in detecting binding-induced modifications to optical confinement and asymmetry.

Conclusions:

• Low-contrast BIC metasurfaces enable single-nanoparticle sensing with high resolution.
• The platform offers position-insensitive response and free-space accessibility.
• This technology is suitable for next-generation biosensing integrated with microfluidics.