The Griess reagent was prepared by mixing 1:1 ratio of 1% (w/v) sulfanilamide (Sigma–Aldrich; St. Louis, MO) in 5% (v/v) phosphoric acid solution (Fluka; Buchs, SG Switzerland) and 0.1% (w/v) Nnaphthylethylenediamine dihydrochloride (NED; Sigma–Aldrich