Carbohydrate-directed Synthesis of Silver and Copper Nanoparticles, and their Antibacterial Property

Abstract

This dissertation work mainly deals with an in-depth study pertaining to the synthesis and characterization of copper and silver nanoparticles based on different carbohydrates, and assessing their antibacterial activity by using agar-well diffusion method. The existing physical and chemical methods of nanoparticle synthesis are expensive and sometimes toxic to environment and human health. Therefore, biological or green synthesis becomes more preferred option currently. Different carbohydrates such as glucose, sucrose, fructose and starch were used successfully for the synthesis of respective nanoparticles having well-defined sizes. The individual reactions went to completion in less than 20 min at room temperature. This method was easy and simple to synthesize high purity of Ag NPs and Cu NPs with different carbohydrates as mentioned above. Gelatin was used to control the agglomeration of the nanoparticles, and acted as a stabilizing agent. UV-Visible spectroscopy had shown a shift of the SPR peak depending upon the different average particle size of Ag NPs and Cu NPs synthesize by different carbohydrates. Visible photoluminescence maximum emission of Ag NPs was observed at 328-345 nm and Cu NPs at 700 nm. The structural and morphological character-ization of the samples was performed using Dynamic Light Scattering (DLS) and Transmission Electron Microscopy (TEM). The carbohydrate-based nanoparticles of this study were found to be effective in growth inhibition of Gram-Negative bacteria namely E. coli; hence showed their antibacterial activity. Starch-based Ag NPs exhibited strong inhibitory effect as compared with other carbohydrate-based Ag NPs and Cu NPs. The diameters of the individual zone of inhibition were noted and compared in this report. Strikingly, starch-based copper NPs showed practically no inhibitory effect on the growth of E. coli. The data clearly suggested that carbohydrate-based silver nanoparticles appear to be more effective in terms of bactericidal activities as compared to carbohydrate-based copper nanoparticles (except fructose-based Cu NP). It is apparent that overall size and shape of the carbohydrate-based nanoparticles are crucial in terms of their inhibitory effect on the microbes. However, the precise molecular mechanisms of antibacterial activities of the individual carbohydrate-based nanoparticles need to be further understood.