Bio-compatible miniature viscosity sensor based on optical tweezers

Viscosity is a fundamental biomechanical parameter related to the function and pathological status of cells and tissues. Viscosity sensing is of vital importance in early biomedical diagnosis and health monitoring. To date, there have been few methods of miniature viscosity sensing with high safety, flexible controllability, and excellent biocompatibility. Here, an indirect optical method combining the significant advantages of both optical tweezers and microflows has been presented in this paper to construct a cellular micromotor-based viscosity sensor. Optical tweezers are used to drive a yeast cell or biocompatible SiO₂ particle to rotate along a circular orbit and thus generate a microvortex. Another target yeast cell in the vortex center can be controllably rotated under the action of viscous stress to form a cellular micromotor. As the ambient viscosity increases, the rotation rate of the micromotor is reduced, and thus viscosity sensing is realized by measuring the relationship between the two parameters. The proposed synthetic material-free and fuel-free method is safer, more flexible, and biocompatible, which makes the cellular micromotor-based viscosity sensor a potential detector of the function and pathological status of cells and tissues in vivo without introducing any exogenous cells.