Abstract
We present the fabrication and characterization of optical fiber reflection probes based on surface-enhanced Raman scattering (SERS) and micro-lensed multimode fibers. For the SERS substrate, a nano-sphere lithography method is used. Comparison of SERS measurements with three different fiber probe configurations is presented. The proposed optimized structure shows a five times increase in SERS signal for dried Rhodamine 6G (R6G) and two times for aqueous R6G in comparison to a standard reflection configuration. Measurements of different concentrations of R6G in a water solution with an limit of detection (LOD) equal to 10−7 M are demonstrated.
Highlights
S URFACE-ENHANCED Raman scattering is orders of magnitude more sensitive than normal Raman scattering, allowing for single molecule detection [1]
We propose a new configuration of surface-enhanced Raman scattering (SERS) reflection probes, where a micro-lensed optical fiber (MLF) is used in combination with a gold film over nano-spheres (AuFON) SERS substrate
The 235 μm MLF found as the optimum diameter for measurements of aqueous samples was used for concentration measurements
Summary
S URFACE-ENHANCED Raman scattering is orders of magnitude more sensitive than normal Raman scattering, allowing for single molecule detection [1]. In this type of sensor the excited SERS has to be collected through the layer of the SERS substrate. This lowers the collection efficiency and for that reason the sample is often dried before the measurements [12], preventing real-time continuous detection applications. We propose a new configuration of SERS reflection probes, where a micro-lensed optical fiber (MLF) is used in combination with a gold film over nano-spheres (AuFON) SERS substrate. We demonstrate the optimization of the MLF diameter and the MLF-SERS substrate distance in a reflection configuration, to maximize the collected SERS for both dried and liquid R6G samples. The probe design is applicable to other SERS substrates; AuFON substrates are attractive in the sense that they are highly reproducible, robust, and cost-effective
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