Biocompatible Fluorescent Core-Shell Nanoconjugates Based on Chitosan/Bi2S3 Quantum Dots.

Bismuth sulfide (Bi2S3) is a narrow-bandgap semiconductor that is an interesting candidate for fluorescent biomarkers, thermoelectrics, photocatalysts, and photovoltaics. This study reports the synthesis and characterization of novel Bi2S3 quantum dots (QDs) functionalized using chitosan (CHI) as the capping ligands via aqueous "green" route at room temperature and ambient pressure. Transmission electron microscopy (TEM), UV-visible (UV-vis) spectroscopy, photoluminescence (PL) spectroscopy, dynamic light scattering (DLS), and zeta potential (ZP) analysis were used to characterize the hybrids made of biopolymer-functionalized Bi2S3 semiconductor nanocrystals. The results demonstrated that the CHI ligand was effective at nucleating and controlling the growth of water-soluble colloidal Bi2S3 nanoparticles. The average sizes of the Bi2S3 nanoparticles were significantly affected by the molar ratio of the precursors but less dependent on the pH of the aqueous media, leading to the formation of nanocrystals with average diameters varying from 4.2 to 6.7 nm. These surface-modified Bi2S3 nanocrystals with CHI exhibited photoluminescence in the visible spectral region. Moreover, the results of in vitro MTT (3-(4,5-dimethylthiazol-2yl)-2,5-diphenyltetrazolium bromide) assay with human osteosarcoma cells (SAOS) cell line demonstrated no cytotoxic response of the nanoconjugates.Furthermore, the results indicated that the Bi2S3 QD-CHI nanoconjugates showed HEK293T cell uptake; therefore, they can be potentially used as novel fluorescent nanoprobes for the in vitro bioimaging of cells in biomedical applications. Graphical Abstract Schematic representation of the biocompatible core-shell nanostructure of the chitosan/Bi2S3 quantum dot conjugates with photoluminescent properties.

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.

Cytotoxicity investigation of luminescent nanohybrids based on chitosan and carboxymethyl chitosan conjugated with Bi2S3 quantum dots for biomedical applications.

Bioengineered hybrids are emerging as a new class of nanomaterials consisting of a biopolymer and inorganic semiconductors used in biomedical and environmental applications. The aim of the present work was to determine the cytocompatibility of novel water-soluble Bi2S3 quantum dots (QDs) functionalized with chitosan and O-carboxymethyl chitosan (CMC) as capping ligands using an eco-friendly aqueous process at room temperature. These hybrid nanocomposites were tested for cytocompatibility using a 3-(4,5-dimethylthiazol-2yl) 2,5-diphenyl tetrazolium bromide (MTT) cell proliferation assay with cultured human osteosarcoma cells (SAOS), human embryonic kidney cells (HEK293T cells) and a LIVE/DEAD® viability-cytotoxicity assay. The results of the in vitro assays demonstrated that the CMC and chitosan-based nanohybrids were not cytotoxic and exhibited suitable cell viability responses. However, despite the "safe by design" approach used in this research, we have proved that the impact of the size, surface charge and biofunctionalization of the nanohybrids on cytotoxicity was cell type-dependent due to complex mechanisms. Thus, these novel bionanocomposites offer promising prospects for potential biomedical and pharmaceutical applications as fluorescent nanoprobes.

One-step colloidal synthesis of biocompatible water-soluble ZnS quantum dot/chitosan nanoconjugates.

Quantum dots (QDs) are luminescent semiconductor nanocrystals with great prospective for use in biomedical and environmental applications. Nonetheless, eliminating the potential cytotoxicity of the QDs made with heavy metals is still a challenge facing the research community. Thus, the aim of this work was to develop a novel facile route for synthesising biocompatible QDs employing carbohydrate ligands in aqueous colloidal chemistry with optical properties tuned by pH. The synthesis of ZnS QDs capped by chitosan was performed using a single-step aqueous colloidal process at room temperature. The nanobioconjugates were extensively characterised by several techniques, and the results demonstrated that the average size of ZnS nanocrystals and their fluorescent properties were influenced by the pH during the synthesis. Hence, novel 'cadmium-free' biofunctionalised systems based on ZnS QDs capped by chitosan were successfully developed exhibiting luminescent activity that may be used in a large number of possible applications, such as probes in biology, medicine and pharmacy.