Fluctuation Correlation Spectroscopy has been used to characterize the optical response of molecules and individual gold nanobeads, in solution. The latter are functionalized or not, and are aimed to be used as new biochemical nanoprobes. All the experiments were carried on an optimized confocal or/and biphotonic microscope in order to detect very weak signals. Several filtering procedures of the fluorescence signal and correlation calculation algorithms were used to precisely analyze the data. I show that the impulsional tensorial response of the microscope has to be taken into account to fit the correlation curves of particles with an anisotropic emission diagram. I have studied three different kinds of nanoprobe. I have proved that fluctuation correlation spectroscopy can be used to characterize fluorescent calcium probes such as Oregon Green Bapta 5N. I have also pointed out the limits of the method. I have enlightened and characterized an unexpected anisotropy of the two photon absorption and emission of the photoluminescence of gold nanospheres. Its interpretation stresses out the importance of the surface states and of the dynamics of the ligands. I have also studied nanoprobes made of a gold nanobead functionalized with chromophores. An original method, based on the hybrid nature of the probe, has been used to demonstrate the heterogeneity of such systems, fluorophore aggregates formation and the very strong quenching of the fluorescence of the chromophores linked to the gold nanoparticles.
