Abstract: We have built several flow cytometers (FCMs) which incorporate the principle of light collection using a flow- stream waveguide (FSW). The smallest and most rugged version uses a diode laser emitting 820-nm light and collects perpendicular light scatter (PLS) with the FSW technique and collects forward light scatter (FLS) with a simple external lens. Both PLS and FLS detectors are silicon diodes with integral preamps; no fluorescence is collected. Two other units have used argon-ion lasers and a dichroic filter to separate PLS and fluorescence, and our studies have examined the factors which limit the performance of FSW light collection for low-level-fluorescence applications. In one case we have used a main-frame laser with line-tunable output and two cylindrical lenses for focusing onto the flow stream. This arrangement has allowed us to detect 93-nm yellow-green beads from Molecular Probes, Inc. and 140-nm green beads from Duke Scientific, Inc. A more recent 'luggable' version incorporates an air-cooled ion laser and a simple spherical lens for focusing the laser onto the flow stream. This FCM was able to detect the 93-nm beads from Molecular Probes. In all cases a flow stream in air is used as an optical waveguide that traps and transports light to one or more detectors. !3
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