Size-controlled silver nanoparticles synthesized over the range 5–100 nm using the same protocol and their antibacterial efficacy

Abstract

A systematic and detailed study for size-specific antibacterial efficacy of silver nanoparticles (AgNPs) synthesized using a co-reduction approach is presented here. Nucleation and growth kinetics during the synthesis process was precisely controlled and AgNPs of average size 5, 7, 10, 15, 20, 30, 50, 63, 85, and 100 nm were synthesized with good yield and monodispersity. We found the bacteriostatic/bactericidal effect of AgNPs to be size and dose-dependent as determined by the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of silver nanoparticles against four bacterial strains. Out of the tested strains, Escherichia coli MTCC 443 and Staphylococcus aureus NCIM 5201 were found to be the most and least sensitive strains regardless of AgNP size. For AgNPs with less than 10 nm size, the antibacterial efficacy was significantly enhanced as revealed through delayed bacterial growth kinetics, corresponding MIC/MBC values and disk diffusion tests. AgNPs of the smallest size, i.e., 5 nm demonstrated the best results and mediated the fastest bactericidal activity against all the tested strains compared to AgNPs having 7 nm and 10 nm sizes at similar bacterial concentrations. TEM analysis of AgNP treated bacterial cells showed the presence of AgNPs on the cell membrane, and AgNPs internalized within the cells.

Assessment of antibacterial activity of two different sizes of colloidal silver nanoparticle (cAgNPs) against Vibrio harveyi isolated from shrimp Litopenaeus vannamei

“…They found that smaller particles have larger surface area compared to the larger particles. Interestingly, these results agree with those presented by Martínez-Castañón et al (2008); Lago et al (2011);Zhong et al (2013); Ivask et al (2014) and Agnihotri et al (2014). However, it is not wisely only to compare antibacterial efficacy of AgNPs on the basis of size in different studies, since it will depend on various factors, such as shape, surface chemistry, crystallinity, capping agent, dose of AgNPs, bacterial strains and composition of culture media (Hosseinpour Delavar 2014;Nafisi Bahabadi et al 2016).…”

Minimum bactericidal concentration of chemically synthesized silver nanoparticles against pathogenic Salmonella and Shigella strains isolated from layer poultry farms

“…Moreover, the bactericidal properties of AgNPs improved by decreasing AgNPsˊ size (Su et al, 2017a). This phenomenon can be explained by the following; when size of AgNPs decreases, the maximum contact area will increase, and the surface area to volume ratio (SA/ V) for each AgNP will then increase, and this resulting in increasing in relative AgNPs concentration (Agnihotri et al, 2014;Swarnavalli et al, 2017). This can be attributed to higher particle penetration and availability of more area of contact between the bacteria and nanoparticles (Swarnavalli et al, 2017).…”

Lignosulfonic Acid Based Hydrogel Nanocomposites for Antimicrobial Application

“…The size of the nanoparticle implies that it has a large surface area to come in to contact with the bacterial cells; therefore, it will have higher percentage of interaction when compared to bigger particles (Agnihotri et al, 2014;Bondarenko et al, 2013). The formation of Ag-NCHs in the copolymeric hydrogel networks can be expected in our current strategy because the silver salts loaded hydrogels are readily reduced by AAm-LSA hydrogels, which immediately turn into dark brown colour.…”