Optical tweezers assisted controllable formation and precise manipulation of microdroplet

Abstract

We demonstrate an optical method to realize controllable formation and precise manipulation of microdroplet using optical tweezers (OT). With the irradiation of a highly focused laser into the mixture of inorganic phosphate buffered saline (PBS) and organic solvent isopropanol, a microdroplet was gradually formed at the center of the trap. The size and the growth rate of the microdroplet could be precisely controlled by regulating the laser power and the proportion of two solvents in the mixture. Furthermore, the microdroplet could be manipulated by OT to build microstructures on the slide. We also discuss the possible mechanism behind our observations and the potential usage of such discoveries.

The formation principle of micro-droplets induced by using optical tweezers

“…To meet the consistency of the experiment, we select the same volume ratio consistent with the previous study (4 : 1 for IPA : PBS). 13 Therefore, the 1 ml of PBS is first diluted with 4 ml of high-purity IPA, and subsequently loaded into the injector as the typical raw aqueous sample in this study. Apart from these, no other ingredients are used.…”

“…Studies suggest that the deformability of the droplet could be affected by the salinity of the aqueous solution 19 , thus the volume ratio of IPA to PBS could directly influence the efficiency of the optical tweezers based droplet generation. To meet the consistency of the experiment, we select the same volume ratio consistent as the previous study (4:1 for IPA: PBS) 13 . Therefore, the 1 ml of PBS is firstly diluted with 4 ml of high-purity IPA, and subsequently loaded into the injector as the typical raw aqueous sample in this study.…”

“…In less than one minute, the size of the generated droplet has increased to more than 10 μm, showing a good growth rate. During this process, the growth can be stopped by interrupting the injection of raw samples, and the growth rate can also be affected by changing the laser intensity or the concentration of PBS to achieve the size controllability (the relevant research of droplet growth rate can refer to our previous research) 13 .…”

“…Such approaches generally rely on the oilwater mixtures, which is easy-stratified and difficult to achieve precise control for meeting the demands of precise transportation and manipulation unless utilizing special microfluidic chips 12 . Concerning this problem, the optical tweezers were introduced and a novel method for the generation of controlled micro-droplets was developed in our previous research 13 .…”

“… 12 Concerning this problem, optical tweezers were introduced and a novel method for the generation of controlled micro-droplets was developed in our previous research. 13 …”