A comparative study on antimicrobial efficacy of non-metallic S, SiO2 and S@SiO2 core–shell nanoparticles

The present work aims to investigate the antimicrobial efficacy of non-metallic sulphur, silica and S@SiO₂ core–shell nanoparticles. The X-ray diffraction (XRD) pattern confirmed that the silica nanoparticles have an amorphous structure. In contrast, the sulphur nanoparticles have a crystalline nature with an orthorhombic α-phase structure and S@SiO₂ nanoparticles suggest the superposition of silica XRD pattern on that of sulphur. UV–Visible spectra of silica, sulphur and S@SiO₂ show the highest absorption peak at 293, 326 and 305 nm, respectively. Fourier-transform infrared spectroscopy (FTIR) spectra of core–shell NPs show the presence of sulphur and silica in the core–shell nanoparticles without any chemical interaction between them. The field-emission scanning electron microscopy (FE-SEM) images revealed that the silica nanoparticles are of uniform spherical shape and the average particle size is approximately 250 nm. The shape of the sulphur nanoparticles was found to be irregular and the average particle size was found to be around 130 nm. The FE-SEM images of the core–shell nanoparticles confirmed the regular spherical shape of S@SiO₂ core–shell nanoparticles with an average particle size of approximately 350 nm. The antimicrobial properties of all the synthesised nanoparticles were examined against animal pathogenic gram-negative bacteria, Escherichia coli, Salmonella and plant pathogenic gram-negative bacteria such as Erwinia amylovora, Xanthomonas oryzae by using agar disk diffusion method. The result shows that uncoated and coated nanoparticles substantially inhibit all the gram-negative bacteria. The results demonstrate that the silica and sulphur nanoparticles show effective antimicrobial efficacy against all the specified bacteria, with concentrations of 1500 and 2000 µg\(/\)ml being the most effective.