Preparation Of Bimetal Au@Ag Nano-cubes And Rapid Detection Of Food Contaminants

Objective:Food safety problems have been frequent occur in recent years,and food contaminants have entered the body through various channels,causing inestimable damage.However,for the detection methods of food contamination,traditional detection methods are now mostly used.There are shortcomings such as large sample volume,complicated processing process,and time consuming,and it is impossible to achieve rapid detection of food contamination on site.At this time,a fast and efficient detection method is urgently needed to ensure food safety.Surface enhanced Raman scattering（SERS）,as an emerging detection method,has attracted the attention of many researchers and has been widely used in chemical,biological,medical and other fields.Because of its high sensitivity,SERS technology requires no pretreatment and low consumption of samples,simple operation,fast detection speed,and the advantages of on-site detection are gradually emerging in the detection field.In this paper,five types of silver-coated gold nanoparticles（Au Ns@Ag NCs）were synthesized,and the Raman detection capabilities of SERS substrates of different sizes for food contaminants were selected to select the optimal substrate.Then,we used liquor-liquor interface self-assembly strategy to build the optimal size Au Ns@Ag NCs single-layer active SERS nanofilm which contains high hot spot density and uniform density.The active Raman platform was used to investigate the practical application of three types of food contaminants:phthalate esters（PAEs）plasticizers,malachite green（MG）,and thiabenzimidazole（TBZ）.Methods:This experiment uses a two-step method to synthesize Au Ns@Ag NCs with different particle sizes.First,Au particles（Au NS）were synthesized using a seed-mediated method,and the subsequent reaction was to adjust the amount of Au NS added to grow nanocubes with different silver shell thicknesses.Subsequently,the best substrate was selected,and the sensitivity and repeatability of the substrate were evaluated using the probe molecule crystal violet（CV）.Then,we choose the Au Ns@Ag NCs aqueous solution as the water phase and the cyclohexane as the organic phase.lastly,we add the inducer ethanol into the liquor to induce a large-scale Monolayer nanofilm between the water phase and the oil phase.The sensitivity and repeatability of this basement membrane were also examined using CV as a probe molecule.Butyl benzyl phthalate（BBP）was added to commercially available drinking water by an external addition method,and the base film was used to detect BBP in the drinking water.Finally,the basement membrane was used to detect MG in fish pond water,and TBZ on orange peel was detected.Results:1.Use two steps to synthesize five sizes of Au Ns@Ag NCs,with regular appearance,uniform size and close arrangement.The side lengths of the five types of nanosquares are approximately 23nm,30nm,39nm,50nm,61nm.By comparing the Raman signal intensities of five types of Au Ns@Ag NCs to the probe molecule CV(10^-6mol/L),it is preferred that the Au Ns@Ag NCs substrate with a size of 50 nm can achieve the strongest Raman signal enhancement effect.Subsequently,five types of side length Au Ns@Ag NCs were used to test BBP(10^-5mol/L),MG(10^-6mol/L),and TBZ(10^-7mol/L),and the results were consistent.Therefore,in this experiment,Au Ns@Ag NCs with a size of 50 nm was selected as the optimal substrate.And using FDTD simulation,the results also show that at 50nm,it has the largest electromagnetic field.Therefore,in this experiment,Au Ns@Ag NCs with a size of 50 nm was selected as the optimal substrate.2.The Au Ns@Ag NCs optimal substrate with a side length of 50nm was assembled into a nanofilm by liquid-liquid interface self-assembly method.The base film was characterized,and the characterization data showed that the nano-squares were closely packed,neatly distributed,and uniform in size.This provides a large number of stable hot spots for subsequent practical application detection.From the experimental results,the sensitivity of the Au Ns@Ag NCs nanofilm to CV can reach 10^-9mol/L,and the repeatable RSD is 8.447%,which has better sensitivity and repeatability than the unformed substrate.Finally,the nano-film substrate was used to detect MG in fish-pond water,TBZ on the surface of orange peel,and BBP in water.The results show that the detection limit for MG in fishing pond water can reach 10^-9mol/L,and the detection limit for TBZ on orange peel surface can reach 10^-9mol/L.For BBP in wine,the lowest poisoning dose can be detected at 1.3mg/kg.It shows that the base film has the ability of practical detection and application of food contaminants,has great potential for rapid detection of food contaminants.Conclusion:In this experiment,a bimetal core-shell structure material was synthesized,which possessed the properties of two single metals,and showed excellent SERS performance.The size can be adjusted by adjusting the amount of gold nanospheres,so that the optimal size substrate can be selected to detect food contaminants.The single-layer nanofilm self-assembled through the liquid-liquid interface has a large area of??uniform and stable hot spots,which not only enhances the detection ability of pollutants,but also has the practical application prospects of being portable and fast and sensitive.