Optical tweezers for trapping in a complex microfluidic environment.

Optical tweezers (OT) are used to manipulate microscopic objects. Due to their lack of physical contact, adhesive forces between the object and the gripping tool do not exist. In general, small objects, such as cells, or glass and polymer beads, are optically trapped in a liquid environment located below a microscope slide. However, for optical trapping applications within microfluidic channels containing thick walls with several layers, and insufficient space available for the optical system, standard OTs are not suited. Further constraints are caused by their limited working distance and space requirements. To tackle this problem, a customized optical system is developed. It provides three distinctive functions of beam shaping, followed by 90° beam deflection, and subsequent beam focusing. After fabrication and characterization, the components are assembled to form a single optical element. The optical system is then integrated in a laboratory setup, which provides a laser source for trapping and simultaneous imaging capabilities to record the optical trapping procedure. Finally, the correct functioning of the OT is experimentally verified.