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

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