Laser-Induced Single Microdroplet Formation and Simultaneous Water-to-Single Microdroplet Extraction/Detection in Aqueous 1-Butanol Solutions

Abstract

Abstract Focused 1064-nm laser beam irradiation to an aqueous 1-butanol (BuOH) solution (7.1–7.4 wt % in H2O) resulted in formation of a single picoliter-volume BuOH droplet. Since water (H2O) absorbs 1064-nm laser light, an aqueous BuOH solution at the laser beam focus is heated via photo-thermal effects and this leads to thermal phase separation of the solution, producing a single BuOH microdroplet. In the presence of a fluorescent dye (10−5–10−7 mol/dm3) in an aqueous BuOH solution, the dye was extracted from the surrounding water phase to the BuOH droplet produced by laser irradiation as demonstrated by in situ fluorescence and Raman microspectroscopies. The present laser-induced water-to-single microdroplet extraction/detection was also extended successfully to that under pressure-driven and electroosmotic flow conditions in microflow devices. In both cases, the single BuOH microdroplets produced by 1064-nm laser irradiation were optically trapped against flow of the solution. Under electroosmotic flow conditions, highly sensitive detection of a fluorescent Al3+-chelate complex injected to an electrophoresis capillary tube was also achieved successfully by single BuOH microdroplet formation and simultaneous extraction of the Al3+ chelate to the droplet by 1064-nm laser irradiation.