Laser-Induced Crystallization of Amino Acids through the Coordinated Effect of Optical Forces and Marangoni Convection.

Laser-induced crystallization through optical trapping offers precise and spatiotemporal control of crystallization kinetics at the microscale region. Here, we demonstrate the optical trapping-induced crystallization of various amino acids, including glycine, l-cysteine, and l-alanine, by focusing a 532 nm continuous-wave laser in amino acid/H₂O solution. The coordinated effect of optical forces and heat-driven molecular delivery improves the local molecular concentration, leading to nucleation and subsequent crystal growth. In situ Raman spectroscopy is employed to investigate the crystallization kinetics and distinguish the crystalline phase. Orthorhombic and monoclinic crystals of l-cysteine are obtained without changing the laser polarization. Further, laser-driven crystal dissolution was observed in the absence of the interface with the morphology evolution recorded. Our work provides an all-optical strategy to control and investigate the crystallization kinetics of amino acids and can be potentially extended to other molecular systems.