Signal enhancement from nanoparticles using dark-field microscopy with grating-coupled surface plasmon resonance

Dark-field microscopy, which detects scattered light from samples, is widely recognized as a label-free detection method. However, sensitively detecting nanoparticles with small diameters and low scattering cross-sections, such as dielectric nanoparticles, remains challenging. In this study, we propose a highly sensitive detection method that enhances scattered light from samples placed on a plasmonic chip capable of grating-coupled surface plasmon resonance (GC-SPR). We investigated how enhancement depends on particle size, illumination and detection wavelength, and polarization conditions. Based on these evaluations, we identified optimal conditions for maximizing signal enhancement. The results demonstrate the feasibility of highly sensitive, label-free detection of dielectric nanoparticles, as well as the potential for their quantitative size estimation.