In situ plasmonic & electrochemical fiber-optic sensor for multi-metal-ions detection

High precision and high throughput detection of heavy metal ions is essential for water quality monitoring and assessment. Herein, we propose a plasmonic & electrochemical dual-mode fiber sensing probe for label-free and real-time detection of multiple ions (Pb 2+ and Cu 2+ as examples). This sensor comprises a multimode fiber-single mode fiber reflection probe, the outer surface of which is coated with a gold nanofilm to excite the surface plasmon resonance (SPR) optically and simultaneously serves as an electrochemical working electrode. In traditional electrochemical detection, the enrichment of ions cannot be detected in real-time. However, by utilizing the plasmonic & electrochemical dual-mode detection method, various kinds of metal ions can be deposited onto the gold nanofilm and selectively oxidized during forward potential scanning, and the entire electrochemical process can be monitored by SPR measurement. We experimentally demonstrate that the sensor can simultaneously detect Pb 2+ and Cu 2+ in a mixed solution in real-time, providing a linear response over the ion concentration range from 10 −12 to 10 −7 M and offering an excellent detection limit (1.69×10 −14 –5.49×10 −13 M). The proposed dual-mode fiber sensor has the benefits of remote sensing, compact footprint, and cost-effectiveness and shows excellent potential for water quality risk management in difficult-to-reach environments.