Flow cytometric immunofluorescence and DNA analysis: using a 1.5 mW helium-neon laser (544 nm)

We evaluate a 1.5 mW HeNe laser (544 nm) for use on an EPICS Elite with a 76 microns Sortsense flow cell. The two applications chosen were immunofluorescence and DNA analysis. We measured the fluorescence threshhold of phycoerytherin calibration beads to be approximately 336 MESF. Cell analysis with a HeNe laser and Argon laser correlated well for the CD4PE, CD56PE, CD19PE conjugates, with correlation coefficients of 0.98, 0.99, 0.94, respectively. The % positive and mean channel fluorescence were comparable to the results obtained with a 15 mW Argon laser. In addition, a three-color configuration yielded excellent results. Cell analysis of CD4PE, CD3ECD and CD19Cy-Chrome with the HeNe laser and Argon laser correlated well with correlation coefficients of 0.96, 0.95, and 0.92, respectively. The histograms showed good separation between the negative cells, the dimly staining cells and the brightly staining cells. Propidium Iodide was chosen for DNA analysis. Full CV values for whole blood DNA fluorescence using the green laser were good at 2.6%. These data indicate the low power 544 nm laser is sufficient to do immunophenotyping and DNA analysis. Results may be explained by higher quantum efficiency and lower background fluorescence. The wavelength of the 544 nm laser is much closer to the excitation peaks of PI, PE, and the tandem dyes ECD and Cy-Chrome. Also, the Raman scattering of water for the 544 nm laser has a longer wavelength maximum than the emission peaks of PI, PE, and ECD. The major advantages of this laser for the research laboratory are small size, no cooling fan, low power requirements and low cost.