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.

Mercury (Hg) is a highly toxic substance; 1,2 it is very difficult to degrade, and easy to accumulate in crops and soil. 3,4 Mercury is introduced into the human body through the food chain, the accumulation of mercury in the body can lead to chronic poisoning, which is a serious threat to human survival and health. 5,6 Since mercury is one of the essential detection items in environmental monitoring, so the quantitative detection of mercury has very important significance.The quantitative detection methods used for mercury include atomic emission spectroscopy, 7 atomic absorption spectroscopy, 8 atomic fluorescence spectroscopy, 9 the UV-visible absorption spectroscopy, 10 inductively coupled plasma mass spectrometry, 11 cold vapor atomic fluorescence spectroscopy and gas chromatography-pyrolysis-atomic fluorescence spectroscopy, 12 liquid chromatography-cold vapor atomic absorption spectrometry and molecular fluorescence spectroscopy. [13][14][15] Among these analysis methods, atomic absorption spectroscopy is the most common, but this method needs a higher requirement for sample preparation and a long detection time. Atomic emission spectroscopy has good selectivity, low detection limit, small matrix effects and high precision, but it requires a highly delicate and very expensive instrument. Atomic fluorescence method has many advantages, such as simple spectral lines, high sensitivity, less interference and a low detection limit. However, the health of operators might be threatened because of mercury vapor generated during operation. UV-visible absorption spectroscopy has a high detection sensitivity and simple experimental equipment, but the method not only requires a long reaction time, but also the specificity of the chromogenic agent is poor. Liquid chromatography-cold vapor atomic absorption spectrometry has a high detection sensitivity and good selectivity. However, the application of this method is limited in most laboratories because it requires expensive equipment. Molecular fluorescence spectroscopy has good prospects because of it's simple operation, fast detection speed, high sensitivity, good selectivity, good reproducibility and low detection limit.

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