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. <i>In situ</i> 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.