| Surface-enhanced Raman spectroscopy（SERS）is increasingly applied in the food safety testing and the quality assessment of agricultural products due to its high detection sensitivity and fast analysis times.The dendritic gold nanostructures are considered as one of the more interesting SERS substrates,being relatively easy to synthesize and displaying high SERs enhancements.Dendritic gold nanoparticles（Au NPs）are particularly attractive as SERS substrates,though shape-controlled synthesis of dendritic Au NPs remains challenge.Dendritic Au NPs were synthesized by reducing chloroauric acid（HAuCl4）with ascorbic acid in aqueous solutions of long-chain alkyl methylpiperidinium bromide（CnPDB）and long-chain alkyl methylmorpholinium bromide（CnMMB）.TEM images showed that the nanostructures had different size and morphology at different concentration ratio of surfactant/HAuCl4.At the ratio of optimum concentration,the dendritic Au NPs with good symmetry and multilevel branches was inside,and the solutions had a broad absorption from about 500 nm to the near-IR region,which was readily assigned to the transverse localized surface plasmon resonances of the Au NPs multilevel branches.As surface-enhanced Raman（SERS）substrates to detect Rhodamine 6G（R6G）,these Au NPs showed excellent enhancement effect with an enhancement factor of105.For the dendritic Au NPs synthesized in aqueous solutions of Cn PDB,the minimum detection concentration of R6G was as low as 3×10-9 mol·L-1,and the linear detection range was3×10-93×10-7 mol·L-1.The relative standard deviation of the results of ten repeated tests was about 612%.The dendritic Au NPs synthesized in aqueous solutions of Cn PDB also showed SERS enhancement effects,for the minimum detection concentration of R6G was around1×10-8 mol·L-1.Thereinto,the linear detection range of Au NPs t was 10-810-6 mol·L-1,and the relative standard deviation of the results of ten repeated tests was about 57%.And the minimum detection concentration of organophosphorus pesticides（parathion-methyl,triazophos and phosmet）on the dendritic Au NPs substrates was down to 1×10-8 mol·L-1.The dendritic Au NPs D and Au NPs T with better SERS enhancement were chosed for the further study.The dendritic Au NPs D and Au NPs T as SERS substrates could also detect organophosphorus pesticide residues of parathion-methyl,triazophos and phosmet at low concentrations of 0.026 ng·cm-2,0.031 ng·cm-2 and 0.032 ng·cm-2(1×10-8 mol·L-1)on apple peels,respectively.The dendritic Au NPs D and Au NPs T substrates afforded detection limits of 3×10-8 mol·L-11×10-8 mol·L-1 in aqueous malachite green,sudanⅠand carmine solutions.In addition to high sensitivity and good signal repeatability,SERS substrates based on these dendritic Au NPs also showed good practicability,which exhibited great potential in the detection of organophosphorus pesticides residues and food colorants.These results suggested that dendritic gold nanostructures introduced here could offer great promise in the field of food safety detection. |
