Facile synthesis of bioconjugated fluorescent CdS nanoparticles of tunable light emission

Abstract

Bioconjugated CdS nanoparticles capped with L-cysteine molecules are prepared by an aqueous route. A new source of sulfur that is a complex of hydrazine hydrate–sulfur is used to develop the aqueous synthesis of these nanoparticles. The change in volume ratio of sulfur and cadmium ions with a fixed molarity of capping molecules, as prepared colloids exhibits different colours. These nanoparticles are characterized by optical absorption, photoluminescence, FTIR, x-ray diffraction and transmission electron microscopic measurements. It is observed that the present technique yields nanoparticles that are spherical in shape whose size ranges from 1.7 to 3.39 nm (estimated from optical absorption). The resulting colloids are highly stable (for more than a few months) and exhibit high quantum yield for fluorescence (close to 34%). This demonstrates that the present route of synthesis is simple and easily scalable to prepare highly fluorescent and biologically important nanoparticles of CdS.