Síntese coloidal aquosa de pontos quânticos luminescentes estabilizados por quitosana e derivados: ZnS, Bi2S3

Abstract

In recent years, the field of colloidal semiconductor nanocrystals, also referred to as colloidal quantum dots (QDs), has grown rapidly. The developments are the result of significant advances in nanoscience and nanotechnology that predominantly focus on biomedical and environmental applications. The interdisciplinary contributions from several areas such as materials science, chemistry and physics, combined with biology, pharmaceutics, medicine and environmental science has created a fascinating new class of hybrid nanomaterials or nanoconjugates. These nanomaterials can be designed and engineered with almost any property or to carry out almost any function. Basically, these nano-sized conjugates combine the intrinsic functions of inorganic semiconductor nanomaterials and the versatile organic biointerfaces offered by polymers (e.g., chitosan, PVA, PEG) and biomolecules (e.g., amino acids, peptides, proteins, DNA). In the realm of inorganic low-dimensional materials for producing nanoconjugates and nanostructures, QDs have been the major choice because of their unique combination of optical, electronic, magnetic and chemical properties, which can be tuned via the modification of the nanoparticle size below the threshold value, named the Bohr radius exciton. Thus, it is reported for the first time in this study, new carbohydrate-based nanoconjugates combining chitosan and carboxymethyl chitosan (CMC) with ZnS and Bi2S3 semiconductor QDs were designed and synthesized via a single-step green aqueous colloidal process at room temperature. These systems were extensively characterized by morphological (SEM, TEM, AFM, DLS, zeta potential) and spectroscopic techniques (UV-vis, FTIR, PL, RMN, and others) in order to access their major structural features and physico-chemical properties. 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 demonstrated that chitosan and CMC were effective polymer ligands for nucleating and stabilizing ultra-small QDs, forming colloidal core-shell nanostructures in aqueous dispersions. In addition, it was verified that variation of pH and molar ratio of precursors during the synthesis affected the physico-chemical properties and morphological aspects of the nanostructures. Moreover, these water-soluble nanoconjugates were photoluminescent under light irradiation. The results of the in vitro assays demonstrated that the chitosan and CMC nanohybrids were not cytotoxic and exhibited suitable cell viability responses toward three cell types. Therefore, it is envisioned that these designed bioengineered nanocomposites can be potentially used as fluorescent nano-sized bioprobes to label cells in vitro, pharmaceutical and environmentally friendly applications