Lanthanide ion modulated dielectric resonance enhancement for nanoscale optical force dye and interferometric scattering microscopy

Nanoscale weak force sensing in aqueous solution is of great interest to researchers from broad areas, including physics and biology. Here we developed a video tracking-based optical tweezers calibration method that enables the detection of the trap stiffness for low refractive index nanoparticles. We found that under resonance conditions, doping lanthanide ions inside a nanocrystal would substantially increase its trap stiffness, achieving a maximum optical trap stiffness of 0.086 pN µm^–1 mW^–1 for 23.3 nm radius nanoparticles. We further use the dielectric resonance effect to modulate the scattering spectrum of single nanoparticles for multiplexed interferometric scattering microscopy.