Carboxymethyl chitosan functionalization of Bi2S3 quantum dots: Towards eco-friendly fluorescent core-shell nanoprobes.

Designed bioengineered nanocomposites are emerging as a novel class of hybrid materials composed of natural aminopolysaccharides and inorganic semiconductors for biomedical and environmental applications. In this study, it is reported for the first time the synthesis and characterization of water-soluble Bi2S3 quantum dots (QDs) functionalized with O-carboxymethyl chitosan (O-CMC) as capping ligands. UV-vis spectroscopy, transmission electron microscopy, dynamic light scattering, zeta potential, and photoluminescence spectroscopy were used to characterize these nanohybrids. The results proved the hypothesis that O-CMC acted as a pH-dependent multi-functional ligand by altering the mechanisms of nucleation, growth and stabilization of water-soluble colloidal Bi2S3 nanocrystals under acidic, physiological and alkaline conditions, using an eco-friendly aqueous process at room temperature. Moreover, the O-CMC capping ligand and the relative molar ratios of the precursors in solution effectively controlled the diameters of the Bi2S3 QDs, which ranged from 2.8 to 12.8nm, and that exhibited luminescent properties in visible light.