Molecular Extraction and Release of an Ionic Liquid Microdroplet With Dynamic Tunability Under Optical Trapping

Ionic liquids (ILs) exhibiting temperature-responsive phase separation offer promising opportunities for microscale extraction when combined with optical tweezers. Here, we induce local phase separation to generate a single IL-rich microdroplet under optical trapping and investigate the dynamics of molecular extraction into, and release from, the droplet using microspectroscopic analysis. At the high laser power, the microdroplet grows and becomes concentrated, thereby promoting molecular extraction. Upon reducing the laser power, the droplet shrinks while maintaining a high IL concentration. During this process, a dense domain forms around the shrinking droplet, accelerating molecular release from the droplet. Furthermore, we find that the local microenvironment experienced by the extracted molecules is governed by the concentration balance between the IL and the solute molecules. These findings elucidate the key factors controlling molecular extraction and release in an optically manipulated IL microdroplet and provide insights into the design of a new single-droplet-based approach for microanalysis.