Flow cytometer, diagram
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The flow cytometer has made the study of lymphocytes subsets possible. The device relies upon a laser to excite fluorescent antibodies bound to specific cell surface receptor. Up to 3 or 4 different colors of fluorescent compounds may be used, excited by different wavelength lasers, so that several subsets can be tagged and studied at once. The instrument can also measure the absorbance of an individual cells nuclear DNA, thus establishing ploidy (i.e., whether a cell is haploid, diploid, or aneuploid).