Bistability-enabled microspheres mass sensing via optical probe in aqueous solution

Optical tweezers possess unique advantages in microparticle properties characterization and dynamics research owing to their non-invasive manipulation and all-optical perception mechanism. In this paper, we demonstrate that the spherical aberration induced by dry-objective optical tweezers generates two stable equilibrium positions for dielectric particles in aqueous media under gravitational effects. The trapping bistability can serve as an all-optical, non-contact methodology for semi-quantitative estimation of single microsphere masses with a relative measurement error of approximately 16%. By counteracting the annihilation of optical forces, we suppress the bistability and the maximum escape velocity has been promoted from 152 µm/s to 650 µm/s, which validated the feasibility of bistability trapping potential well command, and provided a new approach for the dynamic analysis of aqueous optical tweezers.