Light-driven upconversion fluorescence micromotors

Light-driven micromotors with high spatial resolution are powerful tools for targeted drug delivery and biomedical diagnosis. To combine the function of biosensing, light-driven micromotors have been modified with fluorescence materials such as quantum dots or dyes. However, these fluorescence micromotors are generally driven and excited by ultraviolet or visible lights, which may cause photo-damage to biological cells or tissues. Here we propose upconversion fluorescence micromotors (UCFMs) constructed by lanthanide (NaYF₄: Yb³⁺, Er³⁺) doped microrods that were driven and excited by near-infrared lights. The UCFMs were moved to the surfaces of the targeted cancer cells using scanning optical tweezers (SOTs). The upconversion fluorescence spectra were measured to determine the temperatures of the cells, with an absolute sensitivity from 1.71 × 10^-3 to 1.74 × 10^-3 K^-1 and a relative sensitivity from 0.53% to 0.68% K^-1. The UCFMs were then optically driven to actuate the local flow to deliver the polystyrene (PS) microparticles and doxorubicin-loaded mesoporous silica nanoparticles to the vicinity of the cancer cells. By integrating the actuator and sensor into a single device, the UCFMs hold great potential for applications to precise biosensing, single-cell biomedical analysis, and targeted drug delivery.