Photoluminescence and X-ray excited luminescence from glutathione-stabilized gold nanoparticles.

Au nanoparticles coated with glutathione (GSH) were prepared by the heat-assisted reduction of Au(I)-thiol complex at 1:1 or 5:4 molar ratio of Au to GSH. The 1:1 sample has three emissions at 610, 645 and 800 nm while the 5:4 sample has a dominant emission at 800 nm but the two emissions at 610 and 645 nm are very weak. It was found in separations that the 610 and 645 nm emissions are closely related while the 800 nm emission behaves in a different way. By adding NaOH, the 800 nm emission decreases while the red emission increases in intensity at low concentration, but both the red and the NIRL emissions are quenched at high concentrations. The luminescence lifetimes of the red emissions were on the nanosecond time scale while the 800 nm emission was on the microsecond time scale. Based on these observations, it is concluded that the red emission is from a single excited states while the 800 nm emission is originated from surface states. Also, for the first time, X-ray excited luminescence is reported here from Au nanoparticles and the applications of these nanoparticles for cell imaging is also investigated.