Micro-Optics for Optical Trapping in Microfluidics

Micro-optical compo nents offer several possibilities for creating large matrices of optical traps, either when working on inverted microscopes, or by directly integrating miniaturized optical components at the level of a micro-fluidic chip. In thisarticle we focus on two particular configurations, both allowing to generate large arrays of 3D optical traps. The first configuration takes advantage of an array of refractive micro lenses to generate multiple optical tweezers within the focal plane of a high-NA microscope objective. The second configuration relies on an array of focusing high-NA micromirrors which are directly integrated at the level of a micro-fluidic chip. We also present measurements of the maximal optical trapping forces that can be reached with several types of cells commonly employed in biology and biotechnology, and demonstrate that these forces are essentially related to the bulk refractive index of the cells.