| Abstract
| - A visual light scattering detection method of Sudan dyesis reported in food products based on the formation ofsilver nanoparticles (NPs) . Sudan dyes including I, II,III and IV have reducibility due to the nitrogen−nitrogendouble bond and phenol group in their molecular structure, and a redox reaction could occur with AgNO3. Owingto the formation of silver NPs as a result of the redoxreaction, color changes could be observed by eye fromthe red of Sudan to the brown of silver NPs, resulting instrong plasmon resonance light scattering (PRLS) signalscharacterized at 452 nm, which could be measured usinga common spectrofluorometer. It was found that the PRLSintensities were proportional to the dye concentrationsover the range of 0.2−2.4 μM Sudan I, 0.1−2.4 μMSudan II, 0.1−2.4 μM Sudan III, and 0.2−3.0 μM SudanIV, with the corresponding limits of determination (3σ)of 3.2, 3.0, 3.2, and 2.9 nM, respectively. Using hot chilias a model sample, detection could be made with therecovery of 90.8−103.3% and RSD of 4.0−4.9%, and theresults are identical with that of a liquid chromatographicmethod approved by the European Commission. To makethe PRLS method much more practical, we could visuallydetect the quantity of Sudan dyes based on the PRLSsignals using simple devices such as a portable laserpointer (653 nm) and a light emitting diode (458 nm).Mechanism investigations show that the functional groupof Sudan oxidized by AgNO3 is the phenol group, not thenitrogen−nitrogen double bond.
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