Inner wall coated hollow core waveguide SERS probe

Abstract

A hollow core waveguide (HCW) with silver nanoparticles (SNPs) coated on the inner wall has been demonstrated for molecular detection based on surface enhanced Raman scattering (SERS). With rhodamine 6G (R6G) as an analyte molecule and two types of silver nanoparticles (SNPs) as double SERS substrates, the inner wall coated HCW (IWCHCW) exhibits significantly higher sensitivity than previous fiber SERS probes with only one SERS substrate. Two kinds of HCW are used in the experiment, liquid core photonic crystal fiber (LCPCF) and hollow silica waveguide (HSW). SERS signal obtained with either an LCPCF or a HSW IWCHCW is over ten times that obtained in direct detection using a single SERS substrate. The improvement of the SERS sensitivity is attributed to the additional enhancement of the electromagnetic field by the double SERS substrate sandwich structure with one substrate coated on the inner wall of the HCW and the other mixed in the sample solution. Furthermore, With an LCPCF IWCHCW, the SERS signal is around 100 times as strong as that in direct detection when measured from the processed fiber tip. This is attributed to the additional R6G/SNPs solution in the fiber pit, increased coupling efficiency due to surface plasmon resonance in the SNPs in the same region, and further increased electromagnetic field in the same region due to nano-structures introduced during the collapse of the cladding holes. The simple architecture and high sensitivity of the inner wall coated HCW make it promising for molecular detection in various analytical and sensing applications.