Spectro uv vis double

Gold nanoparticles were synthesised by adding 1 mL of the aqueous extract to 19 mL of 0.13 mM gold solution at 25°C. The pH was adjusted to 7 with sodium hydroxide and incubated at 70°C, with a change in colouration and subsequent confirmation by UV-vis spectroscopy (Spectro UV-VIS Double Beam PC scanning spectrophotometer UVD-2950, Labomed, Inc.) ensuring the formation of gold nanoparticles. The biosynthesized nanoparticles were separated from the reaction medium by centrifugation at 14,000 rpm for 15 min at 25°C, the supernatant was removed, and the precipitate was washed in deionised water three times. The size of the nanoparticles obtained was determined by laser granulometry using the Nanotrac Wave granulometer (Microtrac MRB). Scanning electron microscopy (SEM) (JEOL JSM-6010LA) and transmission electron microscopy (TEM; JEOL JEM-2100) were used to confirm the size and morphology of the particles using Formvar grids (carbon-coated copper). The surface chemistry of the AuNPs was analysed by Fourier-transform infrared spectroscopy–attenuated total reflectance using a Cary 630 FTIR spectroscope (Agilent Technologies) (Ahmed et al., 2016 (link)).

The antioxidant activity was evaluated using a method previously described by Hwang et al. [42 (link)]. Briefly, solutions of saponins were prepared in different concentrations (100–1000 μg/mL). The saponin solutions (50 μL) were mixed with the ABTS+ solution (4.95 mL) and incubated for 1 h, protected from light. The mixture was analyzed at 734 nm using a Spectro UV–VIS Double Beam plate reader (Model UVD-3500, Labomed, Inc., Los Angeles, CA, USA). TROLOX was used to create the standard curve. The results were in TROLOX equivalent (TE)/gm. The percentage of inhibition was calculated using the following equation:
where Acontrol represents the control reaction absorbance, and Asample represents the saponin solution absorbance.