Dual fiber optical trapping in a polymer-based microfluidic chip

We present a microfluidic chip in Polymethyl methacrylate ( PMMA) for optical trapping of particles in an 80 mu m wide microchannel using two counterpropagating single-mode beams. The trapping fibers are separated from the sample fluid by 70 mu m thick polymer walls. We calculate the optical forces that act on particles flowing in the microchannel using wave optics in combination with non-sequential ray-tracing and further mathematical processing. We use a novel fabrication process that consists of a premilling step and ultraprecision diamond tooling for the manufacturing of the molds and double-sided hot embossing for replication, resulting in a robust microfluidic chip for optical trapping. In a proof-of-concept demonstration, we show the trapping capabilities of the hot embossed chip by trapping spherical beads with a diameter of 6 mu m, 8 mu m and 10 mu m and use the power spectrum analysis of the trapped particle displacements to characterize the trap strength.