Nitric oxide switches on the photoluminescence of molecularly engineered quantum dots.

The photoluminescence of nonfluorescent molecularly engineered quantum dots (QDs) with iron(III) dithiocarbamates was selectively switched on by nitric oxide. Such functional QDs consisted of CdSe-ZnS nanocrystals as fluorophores and surface bound tris(N-(dithiocarboxy)sarcosine)iron(III) as reactive centers for nitric oxide. The fluorescence of the QDs was quenched by energy transfer between the excited QD cores and the surface bound iron(III) dithiocarbamates due to their optical energy overlapping. Nitric oxide restored the fluorescence of the QDs through reduction of the surface bound iron(III) complexes to iron(I)-NO adducts and thus shutting down the energy transfer pathway. The fluorescence of the iron(III) complex engineered QDs was selectively and quantitatively restored by nitric oxide but not by other reactive oxygen species. Such a property of the functional QDs could be used for sensing nitric oxide based on the fluorescence "turn on" mechanism.