We have developed a new analytical method to detect melamine (MA) in milk powder based on the fluorescence enhancement of Au nanoparticles (AuNPs). AuNPs with the average diameter of ∼16 nm can emit stable fluorescence at 370 nm when the excitation wavelength was selected at 252 nm. The AuNPs could assemble with melamine to form larger aggregates (AuNPs-MA) through electrostatic interaction and coordinating interaction in acidic conditions, which led to the significant enhancement of the fluorescence intensity. Under the optimized conditions, the enhancement of the fluorescence intensity exhibited a good linear dependence on melamine concentration in the range from 8.0 × 10(-10) to 8.0 × 10(-8) M, and the detection limit is 6.1 × 10(-10) M (3σ). This proposed method showed high precision and accuracy when applied to the real sample analyses. In conclusion, a simple, rapid, accurate and sensitive method to detect melamine has been suggested.

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Abstract. In this study, a rhodamine derivative (RH-PY) with dual color (blue green to orange) and multiple response (light, acid gas, and force) was synthesized. The photochromic enhancement behavior of rhodamine derivative in polyurethane matrix was explored. By complexing polyurethane with RH-PY, the open-form lifetime of RH-PY can extend from 3 days to more than one month. To the best of our knowledge, this is the longest open-form lifetime of rhodamine derivatives reported so far. Rhodamine with long open-form lifetime has great potential in developing outstanding photochromic materials. This method is simple and inexpensive, and non-covalent preparation suits for more rhodamine derivatives.