Characterization of selenium nanoparticles (SeNPs)

A small aliquot of about 1 mL of the SeNPs of all the three concentrations i.e. 8 mM, 10 mM and 12 mM was used for UV–Visible spectrophotometer analysis after intervals of 3 h, 24 h and 72 h in order to observe the reduction of Se ions in the reaction mixture. The maximum absorption at the relevant wavelength was noted. The wavelength was set between 100 and 800 nm (nm) and the desired range to observe the peak for SeNPs was 300–800 nm. Double distilled water was used as a blank control in that analysis^4,23–28. The spectrophotometer used for measuring the wavelengths of the SeNPs was PG instrument-t80 UV/Vis Spectrophotometer.

For sample preparation for further characterization tests of SeNPs, the nanoparticle mixture was subjected to repeat centrifugation for 3–4 times at 15,000 rpm for 20 min. after every centrifugation the supernatant was discarded and replaced with deionized water. After final centrifugation, the sample tubes were placed upside down on a sterilized paper towel in order to remove any extra water inside the tube. After 5–10 min the nanoparticles were oven dried and solid nanoparticles were obtained which were further used for Characterization tests^3,4,27.

Fourier Transform Infra-Red (FTIR) Spectroscopic studies were done using Bruker Germany Alpha FTIR spectrophotometer of Bahauddin Zakariya University, Multan, Pakistan²⁷. FTIR analyses were done for the determination of the functional groups present at the surface of the nanoparticles that might be involved in the sorption process. The dried nanoparticle samples were diluted in potassium bromide (KBr) solution. FTIR scan analysis range for the detection of the samples at peaks were between 1000 and 3500 cm^{−14,23,25,26,29,30}.

For determining the size and morphological characteristics of the SeNPs, Zetasizer was employed. Zetasizer is used for the determination of three main properties of nanomaterials like its zeta potential, molecular weight and its size. The method by which the size of the nanoparticle is determined in Zetasizer is known as Dynamic Light Scattering (DLS). This procedure was carried out at 25℃ using Zetasizer Nano S90. Those nanoparticles which showed maximum antimicrobial activity were used to measure the size via Zetasizer^31,32.