Optothermal biophysics: Light driven molecule traps, Microscale Thermophoresis, Imaging of kinetics and Autonomous evolution

Light driven molecule traps. Trapping single ions under vacuum allows for precise spectroscopy in atomic physics. However the confinement of biological molecules in bulk water is hindered by the lack of comparably strong forces. Molecules have been immobilized to surfaces, often with detrimental effects on their function. Here, we optically trap molecules by creating the microscale analog of a conveyor belt: a bidirectional flow is combined with a perpendicular thermophoretic molecule drift [1]. Arranged in a toroidal geometry, the conveyor accumulates a hundredfold excess of 5-base DNA within seconds. The concentrations of the trapped DNA scale exponentially with length, reaching trapping potential depths of 14kT for 50 bases. The mechanism does not require microfluidics, electrodes or surface modifications. It uses the previously found light driven microfluidics of thermoviscous expansion [2][3]. As a result, the trap can be dynamically relocated. The optical conveyor can be used to enhance diffusion-limited surface reactions, redirect cellular signaling, observe individual biomolecules over a prolonged time or approach singlemolecule chemistry in bulk water.