Known toxicity and potential environmental hazards associated with fluorescent semiconductor quantum dots have fueled the search for benign nanomaterials with similar properties. Recently, scientists at Clemson University (Clemson, SC) have demonstrated that surface-passivated nanoscale carbon quantum dots can rival their semiconductor counterparts in terms of spectral features and photoluminescence in solution and in the solid state.
After ablation of a carbon target by a Nd:YAG laser to create the carbon nanoparticles, surface passivation was performed by attaching simple organic species to the acid-treated carbon particles. Depending on the organic species used and the excitation wavelength applied, emissions can cover the visible wavelength range and extend into the near-IR region. Carbon particles 30 to 50 nm in diameter were much less luminescent than dots around 5 nm in diameter. For the smaller particles, emission quantum yield was between 4% and 10% with 400 nm excitation. Confocal-microscope images of E. coli bacteria labeled with the carbon quantum dots show fluorescence at different colors when excited at wavelengths between 458 and 515 nm and detected with long-pass filters at wavelengths between 475 and 560 nm. Contact Ya-Ping Sun at [email protected].