Dual wavelength scanning cytophotometry (Bicoscan).

A computer program has been developed for stage-scanning cytophotometry of double-stained microscopical specimens. The program permits the simultaneous measurement of absorbance values at two wavelengths in each measuring spot. To account for overlap in the absorbance spectra of the two stained endproducts, the program incorporates correction of the measured data to compensate for the contribution of each chromophore to the absorbance measured for the other. The program will compute the corrected local absorbance values at specified wavelengths for each chromophore at each measuring spot and integrate these values over the total object to give separate totals for each stain. It is also possible to have integrated the absorbance values of one chromophore for all those measuring spots where the local corrected absorbance value of the other chromophore exceeds a preset minimum value. When this other chromophore is a nuclear DNA stain, it is possible to obtain an approximate measure of the content of any compound in the nuclear area which can be stained with a chromophore having an absorbance spectrum different from the DNA stain. The validity of the program was investigated on model preparations consisting of two (differently) coloured films of which the absorbance values could be measured either individually or in combination, by partially overlaying one film on the other. The program's potential has been demonstrated by using the combination of either Naphthol Yellow S or dinitrofluorobenzene as protein stains with the Feulgen-pararosaniline(SO2) procedure for DNA in chicken erythrocytes and rat liver cells.