BMS 631 - LECTURE 1 Flow Cytometry: Theory J.Paul Robinson Professor of Immunopharmacology School of Veterinary Medicine, Purdue University

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Summary so far….

•Photodiodes can operate in two modes - photovoltaic and photoconductive •PMTs are usually used for fluorescence measurements

•Photodiodes are usually used for scatter

•PMTS are sensitive to different wavelengths according to the construction of the photocathode

•PMTs are subject to dark current

•Voltages and gain are not linear

•Photodiodes are more sensitive than PMTs but because of their low gain, they are not as useful for low level signals (too much noise)