Illuminating the impact of non-aqueous solvents on optical trapping

The optical trapping of colloidal semiconductor nanomaterials would enable single-particle photophysics, sensing, and chemical measurements. Yet, the trapping of these materials has lagged behind other dielectric and metallic materials due to the prevalence of aqueous solvents in optical trapping experiments, which are not suitable for many semiconductors. Here, we trap particles in multiple solvents and study the impact of non-aqueous solvents on optical trapping dynamics. These experiments and calculations show that there exists an optimal refractive index of the media that maximizes trapping strength, and for semiconductor colloidal nanomaterials, a universal relationship to enhance trap strength. We also find that viscosity has no impact on the trap strength, and only changes the residence times of particles in unstable traps. These results provide an understanding of how solvent selection impacts trapping dynamics and general design rules for experiments in non-aqueous solvents, opening the door for improved sensing, chemistry, and photophysics studies using colloidal semiconductor nanomaterials.