Applications of Silver Nanoparticles on Sensing Technique

ABSTRACT

Silver is a soft, white, lustrous transition metal containing high electrical and thermal conductivity. It is used in different forms like coins, vessels, solutions, foils, sutures, and colloids as lotions, ointments etc. It is the preeminent therapeutic agent in medicine for infectious diseases and surgical infections. Silver nanoparticles possess excellent optical, thermal and electrical properties. Biological and antimicrobial activities have also been owing to their high surface area to volume ratio. So, silver nanoparticles have been utilized as antimicrobial, sensor, drug delivery, opto-electronics devices and in catalysis. Silver nanoparticles can be used for ammonia sensing. Ammonia is generated from the decay of organic compounds, the gas exchange with the atmosphere and nitrogen fixation processes. It is used in various industrial purposes. Ammonia gas is toxic to eyes, nose, throat, skin, membrane and lungs. In the present investigation, synthesis and characterization of Silver nanoparticles (NP), and their application on pathogenic bacteria were investigated. ZnO NP were synthesized by chemical reduction method using starch as capping agent and silver NP was prepared by green synthesis process from AgNO3 solution through the extract of Citrus sinensis (sweet lime). The detail characterization of the nanoparticles was carried out using UV-Vis spectroscopy, Dynamic Light Scattering (DLS) particle size analysis, Scanning Electron Microscopy (SEM), X-Ray Diffraction (XRD) analysis and Thermogravimatric (TGA) analysis. From Dynamic Light Scattering (DLS) particle size and SEM image analysis, the average particle size was found to be 90 nm and 50 nm, for ZnO and silver nanoparticles, respectively. From the analysis of XRD pattern, UV-VIS spectroscopy and TGA, the formation of nanoparticles was confirmed. Antibacterial assay of synthesized ZnO and silver NP was carried out both in liquid and solid growth medium against four pathogens (Escherichia coli, Bacillus subtilis, Pseudomonas aeruginosa, and streptococcus pneumonia). The bacterial growth was monitored by measuring the optical density (OD) of culture solution and estimation of colony forming units (CFU) on solid medium. The effect of NP on the level of gene expression in E.coli was also examined. When NP was administered in the liquid E.coli culture, considerable enhancement of the enzymatic activity of expressed β- glucosidase was observed. Further the physical interaction between bovine α-lactalbumin protein and NP was monitored by DLS particle size analyzer, tryptophan fluorescence and circular dichroism spectroscopy. From DLS particle size analyzer, the protein was found to form stable conjugate with NP. When the interaction was monitored by tryptophan florescence spectroscopy, a drastic conformational change of the protein was observed. It revealed that on binding, nanoparticles caused substantial change in the secondary structure of the protein which indeed in complete agreement with tertiary conformational change monitored by florescence spectroscopy.

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