Experimental Study On Photonic Crystal Fiber Based Surface-enhanced Raman Probe

Optical fiber surface-enhanced Raman scattering (SERS) sensors have attracted significant interest in molecule sensing. The combination of optical fibers and SERS offers the advantages of remote sensing capability of optical fibers and the high sensitivity of SERS. The holey structure of photonic crystal fiber provides an ideal volume for the interaction between the analyte and the light, promising higher excitation efficiency and more analyte molecules involved in the interaction as the light transmitting along the fiber. In this dissertation, SERS probes based on photonic crystal fiber are investigated. The main contents are as follows:1. Hollow-core photonic crystal fiber SERS probe. 1) Hollow core photonic crystal fiber SERS probe has been demonstrated by probing 10-5mol/L Rhodamine B (RhB) molecules. In this probe, the light confined in the hollow core can excite directly the analyte and the SERS substrate on the inner surface of the core. 2) A multi-core SERS probe has been demonstrated based on a seven-core photonic crystal fiber, which provides a multi-channel sensing method.2. Liquid-core photonic crystal fiber SERS probe. 1) A simple method for fabricating selective injection liquid core photonic crystal fibers using fiber fusion splicers is investigated experimentally. The cladding holes are sealed via the fusion process and the central hollow core is left open to the sample. 2) With silver nanoparticles serving as the SERS substrate, low concentration (4.7×10-9mol/L) Rhodamine 6G (R6G) sample has been deteced by the probe. 3) The potential of the liquid core photonic crystal fiber SERS probe for biological molecules has been investigated. PSA (10-6mol/L) and Alpha-synuclein (10-4mol/L) have been detected by the probe.3. Solid-core photonic crystal fiber SERS probe. 1) A novel structure index-guided photonic crystal fiber surface-enhanced Raman probe is presented. The fiber has four big air holes inserted between the solid silica core and the photonic crystal cladding holes, and the four big holes provide a large volume for the interaction between the evanescent wave and the nanoparticles/analyte. 2) The probe has been demonstrated experimentally with gold nanoparticles serving as the SERS substrate, and 10-7mol/L RhB sample has been identified by the probe. 3) A new mothod for fabricating SERS substrate in the air holes has been explored. Gold nanoparticles are synthesized in the holes during the chemical reaction.4. Fiber SERS probe based on two nanoparticles dimer enhancement. A multi-mode fiber SERS probe based on two nanoparticles dimer enhancement has been developed as a highly sensitive SERS probe. The silver nanoparticles with positive charge coated on the fiber tip attract the silver nanoparticles with negative charge in the sample solution. Then the two type nanoparticles buildup a dimmer SERS"hot spot". The Raman signal of the analyte molecules in between can be greatly enhanced. Concentration as low as 10-9mol/L R6G sample can be detected using this probe.