Photoactive Tweezers.

Abstract

The manipulation of micro/nanoscale objects plays a critical role across a wide range of scientific and engineering disciplines. Photoactive colloids, capable of converting low-intensity light into autonomous motion, present a highly programmable platform for micromanipulation. In this work, we introduce a "photoactive tweezers" system based on visible-light-driven, dye-sensitized TiO₂ particles. These particles exhibit positive phototaxis and are autonomously confined within structured optical fields via a self-electrophoretic mechanism. Combining experiments and simulations, we reveal that a circular optical trap creates an effective harmonic potential well with tunable stiffness, controlled by the ratio of the particle size to the optical spot size. Using dynamic light patterns, we further showcase the platform's versatility through shape-tunable confinement, wavelength-selective trapping, and reconfigurable assembly of colloidal lattices. Moreover, we demonstrate that individual or collective active colloids can function as autonomous manipulators, transporting cargo larger than themselves and driving collaboratively assembled micromachines. This approach establishes a robust, flexible, and accessible strategy for advanced micromanipulation and active matter research.