ABSORPTION-SPECTROSCOPY USING MICRODROPLET RESONANCE FLUORESCENCE INTENSITIES

Emission spectra from fluorophor-containing microdroplets exhibit a se ries of sharp peaks due to microcavity effects, superimposed on the us ual broad-band dye emission seen in bulk liquid. The amplitudes of the se resonance peaks are shown here to be sensitive absorption indicator s, and the decrease in apparent resonance intensities may be used as a practical in situ absorption diagnostic procedure in spectroscopy. We illustrate this concept with two examples using a microdroplet stream (with diameters between 13 to 18 mum) of an ethanol/rhodamine dye sol ution, additionally doped with either bromocresol green or cresyl viol et dye. An ability to obtain spectral absorption information, as well as quantitative absorption coefficient estimates in the range of 10 to 10(-3) cm-1, and to infer changes in pH in the droplets is demonstrat ed. Use of this approach in conjunction with suitable indicator dyes s hould permit measurement of specific chemical changes occurring in mic rodroplets.