Fabrication Of 3D Biomemitic Flexible SESR Substrate For Detection Of Pesticide Residues In Fruits And Vegetables

Surface-enhanced Raman scattering(SERS)Spetroscopy is a highly sensitive analytical tool and has been widely used in public security,food safety,environmental monitoring,owing to the advantages of sharp bandwidth,anti-photobleaching,rich molecular information and nondestructive data acquisition.Developping a SERS substrate which could be applied in rapid efficient sampling and direct detection in on-spot assay has been one of the keys of SERS research.Recently,much attention has been paid to the flexible SERS substrate due to its powerful properties that are more suitable for practical application.However,most of the existing flexible SERS substrates are based on fiber paper,tape and graphene,leading to unsatisfied SERS enhancement and reproducibility.Moreover,the existing flexible substrate do not have 3D nanostructures on their surface,which still restrict their microarea sampling efficiency on complex surface.Based on this background,our thesis is devoted to develop a new method for low-cost and simple fabricating 3D gecko-inspired nanotentacle SERS(G-SERS)substrate with the ability of easy to use in sopt analysis,outstanding sensitivity,superior reproducibility and good sensibility,and applying it in rapid efficient sampling and label-free detection of pesticide residues on fruits and vegetables peels.Main researchs and the obtained results are as fellows:(1)A highly ordered AAO was first prepared and served as reuseable template,then the PDMS nanotentacle array was replicated and decorated with Ag NPs via the seeding deposition method,creating high density of “hot-spots”,obtaining the 3D biomimetic SERS substrate.In this work,the type of AAO and seeding deposition time have been optimized.Compared with other substrates,this G-SERS substrate can simultaneously provide outstanding SERS activity(EF=1.2×107),superior reproducibility(RSD=5.8%)and countless flexible nanoscale “tentacles”(~6.7×108/cm~2).Moreover,the high density of “tentacles” can freely approach the microarea and enable efficient target collection.(2)Here,the G-SERS platform is proposed for the first time for the simultaneous detection of three kinds of pesticides via a simple and intuitive “press and peeled-off” approach.By direct sampling from cucumber,apple,and grape surfaces,thiram(TMTD),methyl parathion(MPT),malachite green(MG),and their multiple components have been rapidly and reliably determined.Besides,sampling efficiency,signal reproducibility and stability in practical application have been evaluated.The results indicate,under the optimal conditions,a sensitivity of 1.6 ng/cm~2 for TMTD,0.4 ng/cm~2 for MG,25 ng/cm~2 for MPT,was obtained on peels(S/N=3),and the HPLC test proved no pesticide residue still exist on peel surface after “press and peeled-off”operation.Therefore,the G-SERS substrate could offer a great practical potential for on-spot identification of various pesticide residues on real samples.