An optical fiber microprobe for surface-enhanced Raman scattering sensing with enhanced signal-to-background ratio

Surface-enhanced Raman scattering (SERS) is a highly sensitive and versatile analytical technique that can be implemented on an optical fiber platform for use in challenging environments. This work has sought to address a major factor limiting the use of optical fibers for SERS analytical applications, namely the silica Raman background generated inside the fiber can make it difficult to detect the target analyte. Two different approaches were investigated to address this problem. Firstly, double clad fiber (DCF) was found to increase the collection of Raman scattered signal from the analyte, giving up to twelve-fold improvement in the signal-to-background ratio (SBR). Secondly, a prototype microfilter was manufactured by femtosecond laser machining and attached directly to the DCF tip. Its performance in rejecting background signal was then evaluated. When taking the lengths of the optical fibers into account, the filtered DCF microprobe delivers 7.0 SBR.cm, while the bare DCF probe provided 3.0 SBR.cm. Therefore, the microfilter assembly more than doubled the performance of the SERS probe and, with further optimization in future, it shows great promise for ultra-compact SERS and Raman optical fiber probes.