Pure and Applied Chemistry

Abstract: Laser trapping of molecules and proteins in solution at room temperature is made possible by irradiating 1064-nm continuous-wave (CW) laser with power around 1 W. Although conventional small molecules are not trapped at the focal point, molecules that can form clusters upon assembling and proteins whose size is close to 10 nm are gathered, giving unique assembly structure. Glycine in H₂O shows crystallization, urea in D₂O gives a millimeter-sized giant droplet, and cobalt oxide-filled ferritin protein confirms assembly followed by precipitation. Solute concentration, solvent, and laser power are important factors for determining trapping and assembling phenomena, and the laser focal position is very critical. These unique behaviors are realized by setting the irradiation at the air/solution surface, inside the solution, and at the glass/solution interface. Laser trapping-induced crystallization, liquid/liquid phase separation, and precipitation are compared with the previous results and considered. After summarizing the results, we describe our future perspective and plans.