Hierarchical Assembly of Nanostructures to Decouple Fluorescence and Photothermal Effect

Hybrid nanoparticles are designed and produced by a two-step procedure with the aim to obtain optically controlled multifunctional nanomaterials. In particular, using a sol gel method in alcoholic/water media, silica particles doped with 9-aminoacridine molecules are prepared with a mean diameter of 31 nm, which preserves the fluorescent properties of the dye. In a second step, these nanoparticles are capped with a thin (7 nm-size) gold shell whose growth does not quench the emission of the dye as proven by steady-state and time-resolved fluorescence measurements. The careful choice of the organic dye and the control of the metal layer growth make possible to completely uncouple the fluorescence and the plasmon bands of gold. The selective photoexcitation of fluorescence or plasmon absorption, leading to heat release, has been tested on phospholipidic membranes loaded with the prepared hybrid particles. Under 400-nm irradiation fluorescence is activated, which is used to image the membranes; upon 650-nm irradiation only the gold layer absorbs and efficiently converts light into heat leading to a temperature increase of about 10 degrees C in the surrounding medium which is responsible for the alteration of the membrane architecture.