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

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Ratio circuits

•Ratio circuits are analog circuits which produce an output proportional to the ratio of the 2 input signals.

•They are usually made from modules called analog multipliers.

•Examples are calculation of surface density or antigenic receptor sites by dividing the number of bound molecules by the cell surface area. •E.g. Could use 2/3 power of volume to obtain surface area - but few cytometers make this parameter so can use the square of the cell diameter of scatter instead to approximate.

•pH can also be measured using ratio circuits

•Calcium ratio (using Indo-1) is also used (discussed in later lecture)