(525d) A Novel Approach for the Synthesis of Metallic Nanoparticles on Top of a Tellurium Nanowire Using a Green Synthesis Approach for Biomedical Applications

Statement of Purpose: In a world of constant duality, where the population density increases as much drama as the natural resources disappear, there is some concern that should be addressed from the chemical point of view. Traditional chemistry has undoubtedly enhanced the quality of life, but a price of the threaten of the environment and the health of humans. Chemical processes are responsible for the contamination of all the known ecosystems all over the planet, to more or less extent. The traditional physics-chemical approaches for the synthesis of compounds and drugs that we used for concerns such as the antimicrobial resistance of the fight against cancer are easy-to-get straightforward. Nevertheless, there is a cost associated with the limitations that should be overcome from these approaches, such as the production of toxic by-products or the biocompatibility of the products. Therefore, new methods are needed, and the green chemistry offers itself as a suitable and novel answer, achieving a safe and environmentally-friendly design, manufacture and use of chemical products.

Methods: Tellurium nanowires were prepared using both chemical and green chemistry approaches. For the first one, sodium tellurite was dissolved in an aqueous solution of polyvinylpyrrolidone (PVP), hydrazine monohydrate and ammonia, and keep inside a hydrothermal reactor for several hours. The environmentally-friendly approach led to the use of telluric acid and starch as a unique reducing agent and kept inside a hydrothermal reactor for several hours. Both products were purified using the same conditions and characterized regarding composition, structure, and morphology. Once purified, tellurium nanowires were used as a template for the growth of metallic nanoparticles (such as silver, platinum, and palladium) in a quick method with no need of additional reducing agent at room temperature. Besides, biocompatibility tests of the tellurium nanowires with human tissue were accomplished, growing human dermal fibroblast (HDF) cells in media in the presence of both chemical and green-synthesized nanowires. After an incubation time of 5 days, the cell growth was analyzed using MTS assay. Furthermore, anticancer studies were done using the tellurium nanowires with melanoma cells for 5 days.

Results: It is demonstrated that green synthesized tellurium nanowires can be used as a template for the growth of spherical metallic nanoparticles in a quick reaction that takes places in 1 minute, at room temperature with no need of stirring and reducing agent. TEM images of both tellurium nanowires and metallic nanoparticles were taken, showing nanoparticles with a constant distribution size attached to the tellurium nanowires, which were quickly released from the structure. The chemistry of the samples was confirmed using EDX analysis, showing the distinct peaks of tellurium and the ones corresponding to each one of the metals. In vitro cytotoxicity assays were performed with human dermal fibroblasts (HDF) cells. The experiments showed that green-synthesized nanowires showed a higher cell proliferation of the cells than the experiments carried out with chemically-synthesized structures. Furthermore, after the incubation period, the growth of the cells was enhanced in comparison with the control and the chemically-synthesized nanowires. Anticancer studies showed an enhanced anticancer activity of green nanowires compared to the chemically-synthesized structures over a period of 5 days, causing a higher depletion of cell viability.

Conclusions: Current and main methods to synthesize nanostructures, both nanowires and nanoparticles, use approaches which employ chemical methods. The weakness of these procedures (extreme reaction conditions, production of toxic byproducts, and need of purification) calls for a necessity of alternative approaches. Green chemistry can be used to overcome these drawbacks. Here, green-synthesized tellurium nanowires were compared with chemically-synthesized structures to show that the first ones have an enhanced biocompatibility and anticancer properties over the ones synthesized using traditional methods. Besides, it was demonstrated that tellurium nanowires synthesized using starch can be used for the controllable and quick growth of metallic nanoparticles.