Preparation of nanoparticles by green synthesis and a study on their antibacterial and anticancer properties

Abstract

With a continuous improvement in living standards, humankind's desire for a healthy living environment has become increasingly attractive. However, with the rise of a globalized world and the increase in live-expectancy, contact and exchanges among individuals, and the probability of slight genetic changes, respectively, have become more and more frequent, which also virtually facilitates the spread of infectious diseases and the development of cancer. The rise of medicine has been exposed to every single human being including the possibility of using antibiotics and access to a healthcare system, but it has also failed in other ways. The continued misuse and overuse of antibiotics have led to the spread of antibiotic resistant-microbes (AMR), triggering our jump to the edge of a time in which common diseases that were once easily treated, may kill again. Moreover, cancer, as one of the most lethal diseases in the world, is experiencing an emergence of multidrug resistance behavior towards chemotherapeutic drugs that were designed to inhibit their proliferation. Current treatments based on chemotherapy and radiotherapy are often insufficient, while now they face barriers. Because of the need of new and alternative treatments to fight AMR and cancer, more researchers and physicians have begun to pay attention to nanotechnology, a nanosized world where materials start showing outstanding properties never achieved by their macroscopic configurations. Nanoparticles can destroy the structure of bacterial membranes by binding themselves to the cells, while also they can release metallic ions that will damage the genetic content of cancerous cells. Hence, a broad variety of possibilities and biomedical applications for nanomaterials is now present in front of all of us. Nevertheless, sometimes it is essential to pay attention to how things are made instead of what things are used. Therefore, the traditional synthesis of nanomaterials, based on the use of synthetic chemistry and physics, presents questionable methods related to environmental concerns, such as the production of toxic by-products, or end-user issues, like the lack of biocompatibility towards the target biological tissue. Consequently, new and alternative approaches have been studied, such as those based on the use of natural materials for the generation of nanomaterials, giving rise to what is called "Green Nanotechnology." Therefore, an environmentally-friendly and cost-effective way of synthesizing nanoparticles takes advantages of natural sources, such as bacteria, biomolecules or waste materials. From all of these methods, plant-based and plant-derived biomolecule-based processes are among the most reported and successful, due to their feasibility and reproducibility. Therefore, this dissertation is divided into two parts. In the first section, a starch-derived tellurium (Te) nanowire is used as a template for the in situ generation of noble metallic nanoparticles (palladium (Pd) and platinum (Pt)) and for the generation of a synergetic nanosized tellurium-based nanostructure with powerful antibacterial and anticancer properties, with a promising future as a coating for implantable devices. PtNPs-TeNWs and PdNPs- demonstrated antibacterial properties in a range of concentrations between 10 and 25 μg/mL, triggering no cytotoxicity toward healthy epithelial cells above the same period of time. Moreover, both nanostructures were discovered to have anticancer activity toward melanoma cells in a range of concentrations between 10 and 15 μg/mL with no alteration of healthy skin cells' usual proliferation. On the other hand, the second section is based on the quick and environmentally friendly synthesis of TeNPs using Aloe Vera as a unique reducing and stabilizing agent, showing the generation of a strong synergetic effect between the phytochemicals of the plant and the novel biomedical properties of the metalloid. TeNPs' antimicrobial activity was studied, demonstrating antibacterial activity toward both Gram-positive bacteria and Gram-negative for a range of nanoparticle concentrations between 5 and 50 µg/mL.