Rapid SERS Detection Of Microfluidic Based On Suspended Core Fibers

Surface-Enhanced Raman Scattering（SERS）spectroscopy has the advantages of high sensitivity,"fingerprint"identification,non-destructive detection,etc.It is very suitable for various research based on molecular identification and detection.It has good application prospects in liquid trace detection,and has been widely used in environmental detection,food safety,biomedicine and other fields.The design and fabrication of SERS-enhanced substrates has always been a key issue in SERS detection.In the detection of liquid molecules,conventional planar SERS substrates need to be pre-concentrated,which makes rapid detection in the field impossible.Compared with traditional planar SERS substrates,the unique axially arranged air holes of photonic crystal fibers can be used as liquid chambers,enabling high-sensitivity,real-time,in-situ detection of liquid molecules.However,there are still some problems such as complicated preparation of SERS substrate,weak interaction between laser and analyte,and poor practicability.Based on capillary and suspended core photonic crystal fibers（Su C-PCF）,this thesis proposes a method for direct trace detection of liquid molecules,effectively solves the problem of weak laser intensity at the SERS substrate,improves the practicability in rapid detection,and obtains a highly sensitive and reusable optical fiber SERS probe.It has been used in water environment monitoring,pesticide residues,and other applications.The main research contents and results are as follows:（1）A scheme of SERS trace detection in the liquid environment based on capillarys was proposed and designed.Gold nanoparticles（Au NPs）were pre-mixed with analytes to prepare a SERS-enhanced solution,which realized the rapid trace detection of crystal violet（CV）,one of the pollutants in the water environment.The optimal SERS signal was obtained by optimizing the particle size of Au NPs to form the resonance between the localized surface plasmon and the excitation light.At the same time,grazing incidence and multimode interference in the capillary ensure the effective excitation and accumulation of longitudinal Raman signals.The detection limit of CV is 10^-9 M and the enhancement factor is 10⁸.（2）In order to improve the weak optical field strength of liquid-molecular interaction in capillary and fiber SERS probes,a mechanism of avoided crossings of core mode and surface mode based on Su C-PCF was proposed,which greatly improved the laser power ratio in the liquid channel and improved the SERS sensitivity.To achieve this avoided crossings effect,an efficient fabrication method for SERS substrates was investigated,forming a discrete and densely distributed distribution of silver nanoparticles（Ag NPs）on the inner wall of the fiber.The reaction conditions were optimized to control the deposition of Ag NPs and ensure that this effect occurred near the excitation light wavelength.This Su C-PCF exhibits ultra-high sensitivity with a detection limit of 10^-12 M for CV and an enhancement factor of 10¹⁰.（3）In order to further improve the practicability of Su C-PCF as a SERS probe,Ag/ZnO nanocomposites were modified on the inner surface of Su C-PCF to realize the reusability of the SERS probe.The backbone structure provided by the fiber enables sufficient contact between the laser,the SERS substrate,and the analyte.The Ag/ZnO structure not only improves the detection sensitivity under the synergistic effect of electromagnetic enhancement and chemical enhancement,but also catalyzes the degradation of analytes under UV radiation,making the entire fiber-optic SERS probe reusable.By optimizing the aspect of ZnO nanorods and the adhesion of Ag NPs,the best SERS signal was obtained.The detection limit for the CV solution was 10^-13M,and the enhancement factor reached 10¹¹.The analyte can be catalysed by ultraviolet light,and the probe is still effective after multiple cycles.In addition,trace detection of the thiram aqueous solution in pesticide residue was also carried out,and the detection limit was 10^-9 M.