(700c) Green Synthesis of a Synergetic Structure of Tellurium Nanowires and Metallic Nanoparticles for Biomedical Applications

Statement of Purpose: Health care system is facing significant concerns nowadays such as antimicrobial resistance and cancer. New approaches should be considered, and nanotechnology has been found as a powerful solution to them. Current synthetic methodologies for production of nanoparticles, based on physicochemical standards are known to be 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 lack of biocompatibility of the products. Therefore, new methods are needed, and green chemistry offers itself as a suitable and novel answer, achieving a safe and environmentally-friendly design, manufacture and use of chemical products. In this research, tellurium nanowires were synthesized using a green synthesis methodology (TeNWs). They were characterized in terms of structure and composition and tested for anticancer, antibacterial and cytotoxicity properties. Then, TeNWs were used for the synthesis of metallic nanoparticles in an easy and straightforward method with no need of reducing agent that was completed within 1 minute of reaction. Nanoparticles were characterized, and the synthetic process was compared with the ones described in literature, with the aim to compare the methods in terms of chemical needed, reaction conditions and economic implications.

Methods: Tellurium nanowires were prepared using a hydrothermal reaction. The environmentally-friendly approach led to the use of telluric acid and starch as a unique reducing agent. Once purified, tellurium nanowires were used as a template for the growth of metallic nanoparticles (such as platinum and palladium) in a quick method with no need of additional reducing agent at room temperature. The structure containing both metallic nanoparticles and nanowires was known as synergy. Besides, biocompatibility and anticancer tests of both structures – the synergy and the nanowires - with human tissue were accomplished, growing human dermal fibroblast (HDF) cells and melanoma cells in media in the presence of both nanosystems. After an incubation time of 5 days, the cell growth was analyzed using MTS assay. Furthermore, antibacterial properties were tested against Escherichia Coli and Staphyloccocus Aureus.

Results: It was demonstrated that green synthesized tellurium nanowires can be used as a template for the growth of 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 (Fig.1), 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 the use of green nanostructures, enhanced the growth of the cells in comparison with the control. Furthermore, anticancer and antimicrobial studies showed an improved performance of the synergetic structure compared to the bare nanowires structures, 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...) 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.