Biosynthesis of cadmium sulfide nanoparticles using aqueous extract of Lactobacillus acidophilus along with its improvement by response surface methodology

Although the biosynthesis of nanoparticles by microorganisms can overcome problems associated with common synthesis methods, using pathogenic bacteria, isolating nanoparticles from the cell, and having producing agents in broth media are challenging. This research aimed to biosynthesize cadmium sulfide nanoparticles from the aqueous extract of Lactobacillus acidophilus and improve the biosynthesis process by response surface methodology. The biosynthesis process was conducted by the aqueous extract as a producing, stabilizing, and capping agent, accompanied by cadmium chloride and sodium sulfide solutions as cadmium sulfide precursors in a ratio of 1:10:10, respectively, considering pH and temperature as process variables. Ultraviolet-visible spectroscopy of colloidal aqueous solution showed a peak with an average maximum absorbance of 0.161 +/- 0.023 after 18 h of incubation in un-optimized conditions which was improved up to 0.204 +/- 0.049 under pH 9 and temperature of 50 degrees C in optimized conditions. Field emission scanning electron microscopy indicated monodispersed spherical nanoparticles with an average size of 19.07 +/- 2.54 nm in optimized conditions. X-ray diffraction revealed the formation of cubic/hexagonal crystallites in an amorphous matrix. Fourier transform infra-red spectroscopy determined functional groups involved in the biosynthesis. The findings of this research showed that the bacterium aqueous extract has a good potential for the biosynthesis of nanoparticles.