Speckle tweezers near water-oil and water-air interfaces

Contemporary approaches for multiple optical micro-manipulation typically involve careful pre-engineering of the laser beam shape. In various biomedical and microfluidic scenarios, especially those necessitating unconventional specimen chambers, there is a demand for controlling the collection of micro-objects near fluid-fluid interfaces. For many of these cases, a regular array of trap sites as well as tight confinement are not essential. For such applications near interfaces, we expand on the concept of speckle tweezers (ST), which incorporate randomly distributed light fields for quasi-2D optical manipulation. The proposed technique is demonstrated experimentally by applying ST to govern the movement of polystyrene micro-particles near water-oil and water-air interfaces. The efficacy of the method is validated through the temporal characterization of micro-particle motions, and the confinement of the micro-particles near the interfaces is verified using digital holographic microscopy. However, the methodology has the potential for applications in living cell manipulation, soft functional matter creation, and various industrial processes.