Design, Construction And Performance Study Of Three-dimensional Fiber SERS Prob

Since the first report in the 1990s,optical fiber surface-enhanced Raman scattering(SERS)has attracted widespread attention.It not only has the advantages of high specificity,molecular recognition and huge enhancement of SERS,but also has the ultra-compactness,flexibility,remote sensing and in-situ detection capabilities of optical fiber,making it suitable for environmental monitoring,trace analysis,biochemical sensing and explosive detection.The optical fiber SERS sensor provides a safe technology that can remotely analyze toxic or potentially harmful molecules in hazardous environments,and allows the detection of a small amount(μg/mL)of chemical and biological molecules without any sample preparation and with a short collection time(tens of seconds).For these reasons,optical fiber SERS sensors can be used in the medical field to detect proteins and biomarkers of specific diseases,or as a highly sensitive control system for the concentration of toxic molecules in the environment or food.The fiber SERS substrate has the problems of poor repeatability,low SERS enhancement factor,high preparation cost and complex preparation methods.How to use a simple preparation method to prepare a high stability,high sensitivity and high repeatability optical fiber SERS probe is the key to the practicality of optical fiber SERS sensor.In order to solve the above problems,we have prepared three different types of fiber SERS probes from three perspectives:the design of fiber SERS probe substrate,the construction of three-dimensional nanostructured fiber substrates and the basic research of the performance of fiber SERS probes.Firstly,we propose a three-dimensional SERS optical fiber probe composed of ordered nanocolumn array.The SERS optical fiber probe has good stability and high sensitivity for the in-situ detection of 4-aminothiophenol(4-ATP),and has potential applications in real-time detection of harmful molecules.Then we propose a fiber SERS optical optrode based on ordered nanocavity array structures.Finally,we developed a convenient and effective method for preparing evanescent wave fiber SERS probes based on coated with ordered silver nanocolumn array structures on the curved surface of the exposed fiber core.It is hoped to solve the problems encountered by the fiber SERS probes in the actual sample detection.The main research contents are as follows:(1)In this study,a new method for constructing three-dimensional(3D)SERS fiber probes was proposed.The formation of the 3D optical fiber probe mainly included three steps:construction of monolayer polystyrene(PS)spheres as a mask on the end face of the fiber,reactive ion etching(RIE)for PS spheres and fibers,and metal sputtering deposition.Compared with flat surface fiber probes,these 3D SERS fiber probes are composed of ordered nanocolumn arrays,which have the advantages of a simple manufacturing process,low cost,high sensitivity,and good stability.The structures of the 3D SERS fiber probe can be well controlled by changing the size of the PS sphere and etching time.The formation of the nanocolumn was studied using time evolution experiments.The obtained fiber SERS probe has good stability and high sensitivity for the in situ detection of 4-ATP in solution.Therefore,these 3D SERS fiber probes have potential applications in harmful molecules for real-time detection.(2)In this paper,we have proposed a new strategy to fabricate SERS optical fiber optrodes with ordered gold nanocavities modified by silver nanoparticles(AgNPs)on the fiber tip.Such nanocavity ordered array(COA)structures have strong light trapping ability and improve the utilization of light through multiple reflections of light.Besides,COAs have larger specific surface area,which can provide a large amount of SERS "hot spots",and also enable the absorption of more probe molecules.Furthermore,secondary deposited silver can result in strong coupling between the gold nanocavities and AgNPs.Consequently,the nanocavity arrays can further enhance local surface plasmon resonance(LSPR)effect to improve the sensitivity of SERS optrodes.We have also studied such nanocavity SERS optrodes for in-situ detection of 4-ATP with detection limits of 10-10 M.The SERS optrode is highly sensitive,good reproducibility and acceptable stability,and shows excellent performance in liquid-phase in-situ and remote SERS detection.Thus,it is promising for water environmental monitoring applications.And this paper provides a simple and low cost technology suitable for the large-scale fabrication of highly sensitive optical fiber SERS optrodes.(3)In this study,we developed a convenient and effective method for the fabrication of an evanescent wave fiber probes coated with ordered silver nanocolumn array structures on the curved surface of exposed core.The exposed core optical fiber(ECF)where the cladding has been removed intentionally in order to provide direct access to the evanescent field of the core.Such fibers enable obtain high evanescent field power in the core side and fast liquid infiltration and provide a strong interaction of the evanescent wave with analytes and a long effective pathway of interaction.Besides,the silver nanocolumn array structure coated on the curved surface of exposed core have lager specific surface area which can provide a large amount of SERS "hot spots",and also enable absorb more probe molecules.Furthermore,the silver nanocolumn array structure enhance the local evanescent field surrounding the ECF,not only to excite the target molecules but also have strong light capture for the incident light providing light-matter overlap and enhanced interaction to improve again the sensitivity.And we experimentally demonstrate that the evanescent wave fiber SERS probes can efficiently detect 4-ATP and thiram in situ.We have used a backward scattering scheme and a typical 4-ATP to verify the capacity of the evanescent wave fiber SERS probes,and a low detection limit of 10-10 M is achieved.This paper provides a simple and low cost technology suitable for fabricating a highly effective and good reproducible evanescent wave fiber SERS probe,taking the advantage of the synergy between manipulated ECF properties and silver nanocolumn array structures,and has great potential for label-free sensing and detection of biomolecules.Also this work may provide new insights for the design and preparation of evanescent wave fiber SERS probes with high performances.