Preparation Of Multi-branch Gold Nanoparticles And Its Application In SERS Detection Of Food Safety

In recent years,surface-enhanced Raman spectroscopy?SERS?has been widely used as a new detection technology in many fields due to its high sensitivity and easy for operating.However,all of the stability,repeatability,and enhancement effects of SERS substrates play vital roles in the application of SERS technology,and the lack of them has seriously hindered the SERS application.Therefore,the development of substrates with good stability,repeatability,and sensitivity has been an important issue.Multi-branch gold nanoparticles?AuNPs?possesses a large number of SERS"hot spots"because of their rich tips,edges,and nodes,and therefore shows high SERS activity.Because the shape of AuNPs has a great influence on its SERS activity,at present,researchers have proposed various methods for precise control of the morphology of AuNPs,while among these methods,bolaform surfactants,which are used to induce anisotropic growth of nanomaterials,shows the great advantages of efficiency and speed in AuNPs synthesis.Different bolaform surfactants with nitrogen-containing heterocyclic head groups,such as pyrrole,piperidine and morpholine,and long-chain alkane hydrophobic chains were synthesized.After that,using bolaform surfactants as protectant and L-ascorbic acid as reductant,AuNPs were finally synthesized with plenty of"hot spots",and their optimal growth conditions were simply explored.The images of transmission electron microscope?TEM?showed that the morphology of AuNPs prepared with different surfactants were slightly different.Comparing the enhancement factor?EF?of different AuNPs,it was proved that AuNPs^Y10 performed the most excellent SERS enhancement than the other AuNPs.Moreover,TEM,scanning electron microscopy?SEM?,and X-ray diffraction?XRD?spectra were used to obtain a further characterization information of AuNPs^Y10,which illustrated that AuNPs^Y10 is consisted of several branches with leaves and each branch was symmetric with a plane of them and associated with sharp edges and tips.As the SERS subtrates to detect rhodamine 6G?R6G?,AuNPs^Y10 showed excellent SERS enhancement with the maximum EF value which was two orders of magnitude higher than that of traditional spherical AuNPs,and the minimum detection concentration of R6G is 1×10^–8mol·L^–1.Ten of similar positions on AuNPs^Y10 were randomly selected to examine the uniformity of the substrates.The intensity statistics of R6G used the Raman peak intensity at1357 cm^-1 and the relative standard deviation?RSD?was 8.75%.All of the results indicated that this substrate expressed higher sensitivity and better uniformity in the SERS experiment than traditional spherical AuNPs substrates.Chosing AuNPs^Y10 as the SERS substrate,phoxim,chlorpyrifos,fipronil,and bisphenol A?BPA?were detected and quantitative analyzed,respectivly.After the quantitatibe relationships were established,the limit of detection?LOD?of these substances were calculated,which were4.97×10^–9,5.65×10^–10,4.49×10^–9,and 5.94×10^–10 g·L^–1,and the limit of quantity?LOQ?were1.67×10^–8,1.88×10^–9,1.36×10^–8,1.98×10^–9 g·L^–1.Using AuNPs^Y10 as SERS substrate,phoxim and chlorpyrifos in fruits and vegetables,fipronil in eggs,and BPA residues in plastic packaging beverages were detected,respectively with high recovery rates over 80%.A novel,rapid convenient and highly sensitive SERS substrate for the determination of patulin based on AuNPs^Y10 and the molecularly imprinted technology has been constructed.In order to improve the performance of the molecularly imprinted polymer?MIP?,and obtain a satisfactory sensitive,selective and reproducible SERS substrate,the conditions for using MIP were studied.When pH at 6.0,and incubated for 2 hours,PAT could be detected the maximum SERS intensity.Selectivity was also an important index to evaluate the quality of the MIP and it was proved that MIP can specifically recognize PAT molecules,with a good reproducibility,whose RSD was 12.50%.After the quantitatibe relationship was established,the LOD and LOQ of PAT were calculated,which were 6.93×10^–10 g·L^–1 and 2.31×10^–9 g·L^–1,respectively.The MIP as SERS substrates could be used in detecting PAT content in fruit and vegetable products,such as apple juice,and the recovery rate ranged from 85.29%to 89.34%.