In a 25 mL test tube, 1.0 mL acetate–acetic acid buffer (0.2 M)
with pH = 6, 0.2 mL of Ag-nanoparticle (AgNPs) (100 lM) solution
and 2.0 mL of 0.01 M potassium iodate solution were placed. After
diluting the solution with double-distilled water, the solution was
put in a 1.0 cm quartz cell. The initial absorbance (Ai) at 420 nm
was recorded. After addition of different amounts of tartrazine,
the mixture was equilibrated at room temperature for 70 s. Then
the final absorbance (Af) was recorded at 420 nm. The absorbance
difference was defined as DA420 = Af Ai.