Application Of Quantum Dots And Their Composites For The Analysis Of Nitrite

Nitrite has always been used as food additive.Its wide use leads to high nitrite content in food and water,which is harmful to public health.It is of great significance to develop fluorescence spectrometry for the determination of nitrite because of its high sensitivity,selectivity,simple operation and low cost.Firstly,we synthesized high fluorescence PEI-CdS quantum dots with diameter of 5 nm using hyperbranched polyethyleneimine as stabilizer by simple aqueous phase synthesis method.The formation of quantum dots was confirmed by transmission electron microscopy and ultraviolet-visible spectroscopy.It was found that the fluorescence intensity of PEI-CdS quantum dots increased significantly with the increase of PEI dosage,and remained stable in the pH range of 5.0-9.0.In addition,we also found that nitrite can selectively quench the fluorescence of PEI-CdS quantum dots,and the degree of fluorescence quenching of quantum dots was proportional to the concentration of nitrite,thus realizing the quantitative determination of nitrite.In the range of 1.0×10^-7-1.0×10^-4 M,the linear relationship between fluorescence quenching degree and nitrite concentration is y=10220.62x+1.02（R²=0.999）,and the detection limit is 0.05μM.The detection limit of this method is lower than the maximum limit of nitrite in drinking water(6.5×10^-5M)stipulated by WHO.It can effectively avoid the interference of nitrate ions and other common coexisting anions.We have applied this method to the determination of nitrite in tap water and vegetable samples.Finally,we prepared PEI-CdS quantum dots doped photonic crystal composites and explored the potential of the composites for the detection of nitrite.It was found that the pH value had a great influence on the photonic band gap of PEI-CdS quantum dot doped photonic crystal composites.The composites had a response to nitrite in solution,and the photonic band gap had a red shift with the increase of nitrite concentration,which laid a foundation for the application of photonic crystal composites doped with fluorescent materials in nitrite analysis.