In this project, We develop light-assisted manipulation techniques to control the single object as well as colloidal particles. One of the interesting work involves the utilization of the surface tension change occurs at the liquid-interface due to localized photoswitching of an azobenzene molecule from the cis to trans-state and vice versa. The surface tension change is used to trap the single-particle and manipulation of the particle using the developed photochemical tweezers was demonstrated [1]. In another recent work, we demonstrated that by heating the bio-compatible cost-effective candle soot film using an extremely low-power laser, it is possible to trap a single biological cell as well as a colloidal particle via optothermophoretic forces [2]. In addition, it has been demonstrated that by controlling the laser parameters, it is possible to create the localized assembly of biological cells as well as colloidal particles. The advantage of the reported candle soot-assisted optothermophoretic trapping technique compared to other reported plasmonic substrate-assisted thermophoretic trapping techniques is that it is wavelength-independent. In another particle manipulation technique, we designed and assembled an optical tweezer setup that is coupled with upconversion fluorescence spectral measurement and Raman spectroscopy. Using such a setup, we demonstrated the potential of a single PEI capped upconversion particle for the accurate pH measurement in a flowing medium of biological fluids [3].

1) Angewandte Chemie Int. Edition, 52, 7291-7295 (2013) (DOI: 10.1002/anie.201302111 ) Wiley HOT article - Surfaces and Interfaces

2) Colloids and Surface A: Physicochemical and Engineering Aspects, 616, 126357 (2021)

3) Journal of Materials Chemistry C, 9, 8606-8614 (2021)