Bivariate flow karyotyping with air-cooled lasers

An experimental flow cytometer was constructed using a quartz flow cell optically coupled to a 1.22 NA lens. A pair of crossed cylindrical quartz lenses allowed multilaser excitation. Two helium-cadmium (HeCd) lasers, emitting 16 mW at 442 nm and 35 mW at 325 nm, were used to excite chromomycin A3 and Hoechst 33258 fluorescence, respectively. Bivariate flow karyotypes from normal human male chromosomes and from the Daudi cell line were obtained and were compared to those from a standard instrument using dual water-cooled lasers. The new experimental instrument exhibited comparable resolution to that from the standard instrument. In further experiments with Daudi chromosomes, the 35 mW HeCd laser was replaced with a 10 mW HeCd laser, and the system still gave good, though slightly decreased, resolution.