Visual determination of azodicarbonamide in flour by label-free silver nanoparticle colorimetry

A very practical and competitive sensing strategy for the detection of azodicarbonamide in flour samples was developed by using label-free Ag NPs as a colorimetric probe. Well-dispersed Ag NPs in suspension can form aggregates upon reacting with glutathione (GSH) via Ag-SH covalent bonds and electrostatic attraction, with the color changing from bright yellow to red. However, azodicarbonamide can oxidize the -SH of GSH, preventing the aggregation of Ag NPs. Under the optimum conditions, the A₅₅₀/A₃₉₈ of Ag NPs is linearly related to the concentration of azodicarbonamide in the range of 0.33 μM to 1.7 μM. The proposed method can be used for the detection of azodicarbonamide in flour, with a detection limit of 0.09 μM and recovery between 95% and 97.4% (RSD < 6%). When the azodicarbonamide concentration reaches 0.33 μM, the color change can be detected by the naked eye.