Synthesis, Characterization and Biological Activity Determination of Silver Nanocubes

Abstract

Nanoparticles have been termed as one of the most fascinating findings of science and technology and are finding useful application in almost every field of life. These tiny particles are completely unique from their bulk counter parts as their nanoscale size makes them a great choice for administration in everyday machinery, medical equipment and even in the human body. They have shown great promise in disease diagnosis and prognosis, as drug carriers, and in the treatment of various pathological disorders. Metallic nanoparticles offer an extra advantage of tunable surface plasmon resonance (SPR) which allows them to be targeted by a certain wavelength when inside the body, leaving the tissues undamaged and affecting only the nanoparticles. Silver nanoparticles are among the most widely used metallic nanoparticles in the field of medicine, but the inert antibacterial potentials are by far their greatest hallmark. The antimicrobial and other biological properties seem to be greatly affected by various physicochemical properties of the synthesized silver nanoparticles. Studies have shown that polyol synthesis method is efficient for synthesizing AgNPs of desired shapes and sizes. During the present study we have optimized synthesis of silver nanocubes (AgNCs) using the polyol method. The AgNPs thus synthesized were checked for the desired shape using Scanning Electron Microscopy (SEM). We then investigated antibacterial of the synthesized AgNCs thorough disc diffusion assay, antioxidant activity using FRAP and DPPH assay, hemolytic activity potential, anti-inflammatory activity, and biofilm inhibition potential of these cubical shaped silver nanoparticles through the corresponding biological activity assays. In order to determine the shelf-life of the synthesized AgNCs we also tested the effect of aging on the behavior of these nanoparticles. Our results show that, in general, the cubical AgNPs are less potent in most of these assays as compared to their opposing shapes mentioned in other studies. Our results also indicate that these nanoparticles deteriorate during storage at room temperature in about 6 months as the aged AgNCs did not exhibit any activity at any concentration tested in any assay. vii Antibacterial activity of the synthesized AgNCs was determined using seven different bacterial strains viz., Staphylococcus epidermidis, Staphylococcus aureus, Bacillus subtilis, Bacillus pumilus, Pseudomonas aeruginosa, Escherichia coli, and Bordetella bronchiseptica. The freshly synthesized AgNC samples showed no antibacterial activity against 6 out of seven species of bacteria tested. Bacillus subtilis was the only strain that displayed sensitivity to the freshly synthesized AgNCs discs. Interestingly, these bacteria exhibit a better sensitivity at lower concentration of AgNCs rather than at higher concentration. This observation hints at some kind of uptake mechanism that becomes saturated at the higher concentrations. This hypothesis however needs to be further investigated through experimentation. The freshly prepared AgNC samples exhibited antioxidant activity that was directly proportional to their concentration used in the assay. We conclude that the shape of the NP helps to protect the antioxidant activity of the active ingredient i.e., Ag+ ion. Our results indicate that these AgNCs are safe for clinical usage as they possess no hemolytic activity and they possess significant anti-inflammatory activity. Our results indicate that the AgNCs possess great potential for use in medicine. Nonetheless there is great need for further experimentation to elucidate in detail exact mechanisms of the observed characteristics and validation of their beneficial properties over AgNPs in other shapes.