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  • 1
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A phase-sensitive flow cytometer has been developed that combines flow cytometry and fluorescence lifetime spectroscopy measurement principles to provide unique capabilities for making phase-resolved measurements on fluorochrome-labeled cells and particles. Stained cells are analyzed as they intersect a high-frequency intensity-modulated (sinusoid) laser excitation beam. Fluorescence is measured orthogonally using only a single-channel optical detector. The detector output signals, which are phase shifted from a reference signal and amplitude demodulated, are processed by phase-sensitive detection electronics to resolve signals from heterogeneous fluorescence emissions and quantify single-component decay times. Results show signal phase shift and amplitude demodulation on fluorospheres; a detection limit threshold of 300–500 fluorescein molecules equivalence for excitation frequencies 1–30 MHz; a measurement precision (coefficient of variation) of 1.8% on alignment fluorospheres and 3.6% on cells stained for DNA content; the resolution of fluorescence signals from cells stained in combination with two fluorochromes, based on differences in their decay times; and the measurement of fluorescence lifetimes directly by the two-phase ratio method.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 60 (1989), S. 2924-2928 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A high-speed, normally on, gating circuit has been developed for linear-focused photomultipliers such as the EMI 9816. The gate is capable of attenuating photomultiplier response by 〉5000:1 with a turn-off and turn-on time of 60 and 40 ns, respectively. The circuit is compact enough to fit in a standard photomultiplier housing and has low enough power consumption to run off the photomultiplier high-voltage supply. The high speed and high extinction efficiency make this gate suitable for pulse rejection in low-light level, submicrosecond, time-resolved luminescence measurements.
    Type of Medium: Electronic Resource
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