A SERS-Fluorescence dual-mode fiber sensor for monitoring in FRET system

In a complex Förster resonance energy transfer (FRET) system, it is necessary to monitor the composition change, chemical structural construction or intermolecular interactions. The fluorescence detecting method is not sufficient to supply such information. In this paper, a dual-mode fiber sensor for monitoring in FRET system is proposed. SERS and fluorescence detection can be realized with only one fiber probe. The sensor was designed on separated regions for each mode detections. The sensing capacities was tested, the lowest LOD was calculated to be 1.38 × 10⁻¹⁴ M in SERS detections. A FRET system was simulated with Rhodamine 6G (R6G) and Rhodamine B (RhB). There are FRET, spectra overlap, and competition on substrate between the two dyes, which makes the mixture a typical and complex FRET system. With the proposed sensor, the fluorescence intensity change was monitored, at the same time, a small portion of R6G (1/500 in high concentration and 1/10⁵ in low concentration) in the mixture be recognized with SERS detection. We further detected the illegal addition of Rhodamine in commercially available 100 % orange juice. Even when fluorescence could not detect it, R6G could still be effectively detected by SERS method at a concentration of 10⁻¹⁰ M. By the help of this dual-mode sensing device, the process of chemical reaction in FRET system could be monitored, and more widely applications of FRET technique could be realized.