Preparation Of Nano Molybdenum Disulfide And Applications In Food Analysis

Molybdenum disulfide（MoS₂）is a typical kind of transition metal sulfides.Owing to its unique structure and characteristics,it has become a new two-dimensional material with great potential in different fields.With excellent photoluminescent and nanozyme properties of nano MoS₂,it has attracted more and more affections in the analytical applications.The main contents of this paper are as follows.（1）Sodium molybdate（Na₂MoO₄·2H₂O）,L-cysteine（L-cys）,poly（sodium 4-styrenesulfonate,PSS）were used as the molybdenum source,the sulfur source,the modification reagent separately.Molybdenum disulfide quantum dots（MoS₂-PSS QD_S）modified by PSS were successfully prepared by one-step hydrothermal method.The fluorescence emission peak of the prepared MoS₂-PSS QD_S was located in the ultraviolet region（Em 390 nm）.Since the characteristic absorption（400nm）of p-nitrophenol（p-NP）has a good spectral overlap with the fluorescence emission peak of MoS₂-PSS QD_S.Therefore,p-NP can be quenched by the fluorescence of MoS₂-PSS QD_S through the inner filter effect（IFE）.Based on the IFE,a new method for high-sensitivity and high-selectivity fluorescence analysis of p-NP was established.This method has been successfully applied to the detection of p-NP in environmental water samples.（2）Sodium molybdate（Na₂MoO₄·2H₂O）,L-cysteine（L-cys）,sodium cholate（SC）were used as the molybdenum source,the sulfur source,the modification reagent successively.Molybdenum disulfide quantum dots（MoS₂-SC QD_S）modified by SC were successfully prepared by one-step hydrothermal method.Curcumin（Cur）has a characteristic absorption at 440 nm,it has a large spectral overlap with the fluorescence emission peak of MoS₂-SC QD_S at 460 nm.The mechanism of action between Cur and MoS₂-SC QD_S were the fluorescence resonance energy transfer mechanism（FRET）.the fluorescence emission intensity log（I₀/I）of MoS₂-SC QD_S at 460 nm was linear with the concentration of Cur.This method was successfully applied to the determination of curcumin in food.（3）Sodium molybdate（Na₂MoO₄·2H₂O）,L-cysteine（L-cys）and iron were used as the molybdenum source,the sulfur source,the modification reagent successively.Fe-modified molybdenum disulfide nanosheets（MoS₂-Fe NS_S）was successfully prepared by one-step hydrothermal method.MoS₂-Fe NS_S possessing the properties of peroxidase have been found,which can catalyze the color reaction of H₂O₂ with 3,3,5,5-tetramethylbenzidine（TMB）.The glucose oxidase was used to catalyze the oxidation of glucose to produce H₂O₂,the generated H₂O₂ reacted with TMB under the catalytic action of MoS₂-Fe NS_S;the absorbance（452 nm）of the solution after the reaction has a good linear relationship with the glucose concentration.Based on the above principles,a new method for the determination of glucose in fruits was established.At the same time,the feasibility of this analysis system to achieve digital colorimetric analysis was studied.Taken mobile phone photographs of the solution of the above catalytic oxidation color reaction system and deal with the results of images with Image J software,We found that the reaction system solution with different glucose concentrations corresponding to the photographed images.There was a good linear relationship between the average optical density（AOD）of the photographed images in the reaction system solutions with different glucose concentrations.The glucose content in different fruit samples was determined by instrumental method and digital colorimetric method respectively;the results of the two methods were not significantly different.