An integrated instrumentation for light-scattering and time-resolved fluorescence measurements

An integrated instrumentation which combines in the same system static and dynamic laser lightscattering and time-resolved fluorescence spectroscopy is described. The two types of measurementscan be performed simultaneously on the same sample contained in a thermostated cuvette. The lightscattering allows measurements of molecular weights and hydrodynamic radii in the range of 20 8,to a few micrometers. The overall time resolution of fluorescence measurements is around 50 ps.The system provides the simultaneous acquisition of the tluorescence decay curve, of the timeintegrated emission spectrum, and of two time-gated spectra. The light-scattering technique givesinformation on the global structure of the aggregates, while fluorescence measurements are sensitiveto the local interactions of a fluorescence probe with the surroundings. The contemporary use ofthese two complementary techniques can be quite valuable mostly for biological samples for whichstability and reproducibility with time can sometimes be a problem. As an example, combinedmeasurements of the dimension of dimyristoylphosphatidylcholine vesicles around theirtemperature transition and of fluorescence lifetimes of the diphenylhexatriene probe incorporated inthe vesicles is shown.