Synthesis, characterisation and antimicrobial effect of starch capped silver sulphide nanoparticles against Escherichia coli and Staphylococcus aureus

Abstract

Silver sulphide nanoparticles were synthesised at room temperature using a green synthetic method. Silver nitrate and thiourea have been used as the sources of silver and sulphide ions, respectively. Starch was used as the capping agent while water was used as the solvent. The effect of precursor and capping agent concentrations was investigated for their influence on the size and shape of the synthesised nanoparticles. The concentrations were varied in the ranges 0.1-;0.6 g and 0.25-1 g for the precursor and capping molecule, respectively. The nanoparticles obtained were spherical and cubic shaped with size distribution of 7-31 nm. Absorption spectra gave blue shifted band edges with Stokes shift of 2 nm. XRD patterns were confirmed to have monoclinic crystallinity with α-phase. FTIR results showed that the nanoparticles were successfully capped with starch capping agent. Increasing both the precursor and capping agent concentrations resulted in a decrease in the nanoparticle sizes. The antibacterial activity of Ag2S nanoparticles against Escherichia coli and Staphylococcus aureus showed susceptibility towards the Gram negative and positive bacteria, respectively. The lower precursor ratio had the lowest minimum inhibitory concentration (MIC) of less than 0.023 mg/ml, while the higher precursor ratios had MIC value of 0.046 mg/ml. The growth curve studies of bacteria treated with nanoparticles showed an increase in growth and then a decrease as the exposure time was increased. This indicated that the growth inhibition is dependent on time exposure of the bacteria to the nanoparticles.