Abstract

Flow cytometers fabricated from polymers instead of glass usually have poor signal- noise ratios because of background fluorescence. We describe a configuration that largely rejects background fluorescence using the flow channel as a leaky optical waveguide. Conventional flow cytometers use glass or silica flow cells to focus hydrodynamically a stream of particles such that each particle passes through the detection volume singly. Polymer devices suffer from the disadvantage of high background fluorescence when fabricated from commodity polymers. To avoid this problem, we have used an optical configuration in which both the side scatter (SSC) and the fluorescence (FL1) are collected through the flow channel which itself forms a waveguide for the detected photons. This waveguide uses Fresnel reflections which occur at the interface between the polymer walls of the channel and the channel contents. We have produced disposable polymer microfluidic structures and applied this detection method, allowing us to detect side scatter from particles down to 308 nm diameter.

© 2004 Optical Society of America