Making gold nanoparticles fluorescent for simultaneous absorption and fluorescence detection on the single particle levelElectronic supplementary information (ESI) available: Experimental setup; absorption and fluorescence spectra of 20 nm gold NPs solution; SEM, AFM and photothermal imaging of 20 nm gold NPs; calculations of the fluorescence quantum yield; photothermal and fluorescence imaging of 20 nm gold NPs after solvent exchange. See DOI: 10.1039/c0cp01389g

We demonstrate a simple way of making individual 20 nm gold nanoparticles fluorescent (with a fluorescence quantum yield of about 10 −6 ) in glycerol. Gold NPs prepared in such a way have bright fluorescence for a long time under moderate excitation, and their fluorescence remains when the solvent is exchanged to water. We propose to use these nanoparticles as a calibration standard for simultaneous detection of fluorescence and absorption (by means of photothermal detection), and experimentally demonstrate the theoretically predicted shift in axial positions of these signals. Simultaneous absorption and fluorescence detection of such stable labels makes them attractive for multidimensional tracking and screening applications. The fluorescence of single 20 nm diameter gold nanoparticles is increased several orders of magnitude upon a controlled moderate local heating by a laser beam.