Dual-Laser Optical Tweezers for Photothermal Analysis of Hybrid Microgels

Soft actuators that respond to external stimuli play a fundamental role in microscale robotics, active matter, and bio-inspired systems. Among these actuators, photo-thermal hybrid microgels (HMGs) containing plasmonic nanoparticles enable rapid, spatially controlled actuation via localized heating. Understanding their dynamic behavior at the single-particle level is crucial for optimizing performance. However, traditional bulk characterization methods such as dynamic light scattering (DLS) provide only ensemble-averaged data, thereby limiting analytical insights. Here, a dual-laser optical tweezers approach is introduced for real-time, single-particle analysis of HMGs under controlled light exposure. Combining direct imaging and mean-squared displacement (MSD) analysis, our method quantifies the precise laser power required for actuation and accurately tracks the particle size. The results are benchmarked against dual-laser DLS, demonstrating comparable precision while offering the unique advantage of single-actuator resolution. Thus, this method provides a robust platform for precise optimization of programmable actuators with applications in soft robotics, microswimmers, and biomedical devices.