EFFICIENT DETECTION OF SINGLE MOLECULES ELUTING OFF AN OPTICALLY TRAPPED MICROSPHERE

We demonstrate efficient detection of single fluorescent molecules elu ting off a polystyrene microsphere optically trapped in a flowing shea th stream. A 1 mu m diameter analyte doped microsphere was positioned similar to 20 mu m upstream of a 16 mu m diameter probe laser without significant degradation of the detection signal-to-noise ratio due to scattered laser light and fluorescence from the microsphere. In compar ison to more standard capillary sample introduction, the microsphere c auses only small perturbations to the sheath fluid how. The small diam eter of the analyte stream eluting from the microsphere results in a g reater than 90% detection efficiency for single rhodamine-6G molecules , limited primarily by the photostability of the dye.