Evaluation of the Spatial Distribution of Temperature of Aqueous Solutions under the Conditions of Laser Trapping for Molecular Assembly.

The spatial distribution of the temperature of aqueous solutions under the conditions of laser trapping for molecular assembly was systematically evaluated. Recent studies have revealed that laser trapping (also called optical tweezers) is a powerful tool not only for manipulating micro/nanoparticles but also for controlling molecular assembly, such as crystallization. However, laser trapping for molecular assembly usually requires focused laser irradiation with a power of ∼1.0 W, which should cause a higher temperature elevation in a larger region compared to that for conventional optical tweezers (<0.1 W). In this work, the ratio metric measurement of thermoresponsive fluorescent protein revealed the actual spatial distribution of temperature rise in a relatively wide field of view (∼100 μm) and a wide range of irradiation time (seconds to minutes) at the laser power of 0.1-1.0 W, highlighting the impact of temperature elevation on molecular assembly over the laser focal spot size (∼1 μm). We also found the confinement of photothermally generated clusters by laser trapping at the laser focus, which indicates a synergistic interplay of laser trapping and photothermal effects on the aggregation of thermoresponsive polymers above the lower critical solution temperature. We foresee that the photothermal effects on molecular assembly studied in this work should enhance the understanding of the underlying mechanisms of molecular accumulation/aggregation induced by laser trapping.