Biosynthesis of gold and silver nanoparticles using solanum lycopersicum fruit extract: process optimisation, characterisation, and their potential applications

2017-02-27T23:21:55Z (GMT) by Lee, Boon Seng
Recent advances in nanotechnology offer new possibilities in a wide range of applications. Despite the seemingly unlimited potential of nanotechnology, there is growing concern about the potential health and environmental impacts of the production and use of nanomaterials produced using the conventional methods. Recently, plants have been successfully used for the synthesis of nanoparticles in a nontoxic and environmentally benign manner. However, the potential applications of these biosynthesised nanoparticles are yet to be fully explored. The main objective of the present study was to develop and optimise a biological method for the synthesis of gold and silver nanoparticles, utilising tomato fruit extract as a reducing and stabilising agent. The nanoparticles obtained were characterised and compared to those produced using a chemical method. Scanning electron microscopy equipped with energy dispersive X-ray analysis confirmed the identity of the biosynthesised nanoparticles. The effects of pH, extract concentration, and temperature on the size, size distribution, and shape of nanoparticles were investigated. High temperatures and high pH were found to increase the production rate of nanoparticles, favouring the formation of monodisperse and smaller-sized nanoparticles. The biosynthesised gold and silver nanoparticles exhibited the characteristic plasmon absorption peaks, which centred at approximately 530 nm and 410 nm, respectively. In addition, the nanoparticles were observed to have a net negative charge and were crystallised in a face-centred cubic structure. Fourier-transform infrared spectroscopy analysis indicated that the nanoparticles were capped with biomolecules derived from the tomato extract. Biosynthesised gold nanoparticles were shown to bind efficiently to a synthetic metal-binding polypeptide, implying their potential in therapeutic delivery applications. In a follow-up experiment, the ESAT-6 antigen from Mycobacterium tuberculosis was fused with the metal-binding polypeptide and successfully expressed in Nicotiana benthamiana leaves, with recombinant protein yields ranging from 0.01% to 0.23% of total soluble protein. The recombinant proteins were purified and their identities were confirmed by western blot showing the expected molecular weights. The purified proteins were conjugated to three different samples of biosynthesised gold nanoparticles covering different size ranges. The resultant AuNP-GBP:ESAT-6 conjugates were then used to immunise C57BL/6 mice. The results showed that GBP:ESAT-6 formulated with AuNPs with an average size of 10.3 nm induced elevated antigen-specific immune responses. In addition, no toxic effects were observed in mice treated with the biosynthesised AuNPs. Taken together, this study provides an additional evidence with respect to the use of plant-derived materials as an eco-friendly, nontoxic and viable approach for the synthesis of nanoparticles.