Evaluation of Antioxidant Activity: DPPH and ABTS Assay

In vitro antioxidant activity of AgNO_3, MA-extract and MA-AgNPs (concentration 100–500 μg/mL) was investigated by 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2′-Azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radical scavenging assays. DPPH assay was conducted according to standard protocol25 with slight modifications. In brief, 100 μL of 0.1 mM DPPH was added to 100 μL of different concentrations of AgNO₃, MA-extract and MA-AgNPs and the mixture was incubated at RT for 30 min in the dark. Absorbance value of the decolorized solution was taken at 517 nm. The free radical scavenging activity against ABTS radical was evaluated by standard procedure26 with slight modifications. In brief, 10 mL of 7.4 mM ABTS was mixed with 10 mL of 2.45 mM ammonium persulfate and the mixture was kept at RT for 16 h in the dark.100 μL of ABTS was added to 100 μL of sample and solution was incubated at RT for 20 min in the dark. Absorbance (A) value was taken at 734 nm. In both these experiments, butylated hydroxytoluene (BHT) was used as the reference standard. Control was prepared without sample. Percentage inhibition was calculated using the following equation: