Intraparticle Energy Transfer and Fluorescence Photoconversion in Nanoparticles:  An Optical Highlighter Nanoprobe for Two-Photon Bioimaging

We report organically modified silica nanoparticles co-encapsulating two-photon fluorescent dye aggregates and a red-fluorescent energy acceptor, where the latter is indirectly excited through intraparticle energy transfer following two-photon excitation of the former. In vitro two-photon microscopy has demonstrated that these nanoprobes are avidly internalized into cells with bright acceptor fluorescence and that cellular optical highlighting is effected with red-to-green photoconversion by selective acceptor bleaching, while keeping the donor and the nanostructure of particles intact.