Cyclodextrin Modified Silver Nanostructures As SERS Substrate For The Detection Of Polychlorinated Biphenyls

Raman spectroscopy is a powerful tool for qualitative analysis, which could provide abundant information of the analyte structure base on the vibrational modes. The Raman scattering effect was discovered by C.V. Raman in1921in India. Surface-enhanced Raman spectroscopy (SERS) is an enhanced Raman signal on a metal substrate. SERS technique as a sensitive and selective method is widely used in the environmental analysis.Polychlorinated biphenyls (PCBs) are known as a kind of Persistent Organic Pollutants (POPs), which posed an importance in the detection of its residues. In this study, a SERS-active substrate was fabricate, which was used to detect the low concentrations of PCBs dispersed in water. The stability and the reproducibility of the SERS substrate are improved with the development of the materials science and nanotechnology. Above all, SERS detection with a simple and an efficient device will be a promising investigation. The main research work is described as follows:1. Cyclodextrin modified SERS-active substrate was used to detect low concentrations of PCBsCyclodextrin ((3-CDs) could be used as receptor to capture PCBs molecules in solution with a special molecular structure-hydrophobic internal cavity and hydrophilic external surface. β-CDs used in our experiment were modified with-HS group, which was characterized with FT-IR、Raman spectroscopy and EA. The CD-modified Ag substrates were fabricated by the galvanic displacement (GD, also known as electroless deposition) reaction on commercial copper foils. The Tollen’s reagent ([Ag(NH3)2]+) as the silver precursor was reduced and the nanostructured Ag films were formed on copper foils. The components and micro-morphology of the prepared Ag-coated-Cu (Ag-Cu) film were confirmed by XRD and SEM. PCB15and PCB77were used as probe molecules for SERS detection with different concentrations. Comparison with the absence of HS-CD, the CD modified on the silver film can enrich the PCBs molecules via host-guest interactions. The enhancement factor of the SERS substrate was obtained according to the fingerprint (1600cm-1).2. Sensitive SERS Detection of PCBs by Forming "Hot Spots" from "Sandwich" Host-Guest InclusionThe cavity of cyclodextrin could be matched with PCBs according to our theoretical calculations, which could be inclusion complexes via host-guest interactions. Above all, cyclodextrins were introduced as a bridge bond in our experiment to link two silver nanoparticles. We fabricated "sandwich" structure-Ag|CD-PCB-CD]Ag with coupling effect in SERS detection. PCB77as probe molecule was detected in our SERS experiment via Ag|CD-PCB-CD|Ag substrate, which exhibited more significant enhancement factor than our previous2D substrate. The "sandwich" structure was confirmed by XRD. TEM、SEM、FT-IR and Raman spectroscopy.