In this report, spherical silver nanoparticle (AgNP-sp) and rod-shaped silver nanoparticle (AgNR) were prepared by chemical reduction method and their antibacterial activity against various Gram-positive and Gram-negative bacteria had been evaluated for their efficiency. Minimal inhibitory concentration (MIC) tests were conducted to study the antibacterial properties, and substantiated with killing kinetics of silver nanoparticles (AgNPs). The study revealed that both AgNP-sp and AgNRs are good antibacterial candidates. Bacterial sensitivity to nanoparticles (NPs) was found to vary depending on microbial species. Disc diffusion studies revealed the greater effectiveness of AgNP-sp and AgNR against Klebsiella pneumoniae AWD5 at the doses of 249 and 392 µg. The dose dependent activities of prepared NPs were also observed on the batch studies of disc diffusion and MIC with various strains. The optical and morphological structures of NPs were analyzed by UV-visible, XRD, FE-SEM and TEM. Further, FESEM of bacterial culture treated with AgNPs confirmed antibacterial activity of NPs by showing rupture of bacterial cell wall. Also, the genome of test organism was found to have CusCFBA and CusRS operons. The killing kinetics confirmed that the death rate of K. pneumoniae was higher against AgNP-sp as compared to AgNR.

In the present study, tri-sodium citrate has been used as both the reducing agent and stabiliser for the synthesis of silver nanoparticles (AgNPs). Sodium borohydride (NaBH 4) was used in various concentrations. The absorbance of AgNP solution was measured after the addition of NaBH 4. The samples were characterised by ultraviolet-visible spectroscopy after 5, 10, 15, 25, 60 and 120 min of synthesis to investigate the stability of AgNPs for different concentrations of NaBH 4. Transmission electron microscopy revealed the nanostructure of the prepared samples with average sizes as 18, 20 and 29 nm. Photoluminescence spectra of these AgNPs showed maximum emission at wavelengths 473, 470 and 469 nm, respectively, when excited at 350 nm. Further, Disk diffusion test showed that all the prepared samples are good candidates for antibacterial activity while AgNPs of average size 18 nm were found most effective against the tested Grampositive and Gram-negative bacteria.

Spherical bare silver nanoparticles (AgNPs) and silica coated silver nanoparticles (Ag@SiO 2 ) have been prepared by one step chemical reduction method. The optical, structural and morphological studies were done by UV-Vis absorption spectroscopy, X-ray Diffraction (XRD) andTransmission Electron Microscopy (TEM). The antibacterial effects of AgNP and Ag@SiO 2 were further compared based on diameter of zone of inhibition and minimum inhibitory concentration (MIC) test against B. subtilis AST5-2, S. aureus ATCC 25923, S. marcescens AL2-16, and K. pneumoniae AWD5. Enhanced antibacterial activities were observed for Ag@SiO 2 core-shell NPs as compared to AgNPs against all tested bacteria. The results were attributed to the prolonged release of Ag (I) through porous silica shell that inhibits the growth of tested bacteria and also infers the possibility to be used in potential antibacterial applications.

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