In the last decades, the plasmonic effect of metallic nanoparticles (NPs) has been broadly exploited for label-free optical sensing. To analyze the scattered light from NPs, dark-field microscopy is the most employed technique, which typically requires complex and expensive set-ups. To overcome these limitations, here, we propose a new methodology to develop plasmonic sensors. In our approach, gold nanoparticles (AuNPs) are bonded to the end-face of convectional multimode optical fibers (MMFs). The measuring set-up is as follows: light is launched from a white light source to the end of the MMF where AuNPs are located. The guided light interacts with the AuNPs where localized surface plasmons are excited. The absorption and reflection spectra are analyzed with a miniature spectrometer. Our system is robust, portable, cost effective, and operates in the 250-1200 nm wavelength range. Moreover, the acquisition of data is in real time. Instead of monitoring the conventional shift in the plasmon resonance, our strategy relies on the plasmon resonance energy transfer (PRET) from functionalized AuNPs to metal ion complexes build on top of the AuNPs surface. Our methodology facilitates the detection of copper ions (Cu2+) in water (<10^(-9) M) by the formation of conjugated resonant complexes of N-[3-(trimethoxysilyl)propyl]ethylenediamine (TMSen). By applying our technology, new emerging, fast, and cheaper devices with intrinsic high sensitivity can be developed for the detection of different heavy metal ions in water, which are harmful to the environment and human health.
Ángel Ortega, Javier Barroso , Joseba Zubia, Fernando Benito, Joel Villatoro, and Lourdes Basabe, "Fiber optic sensing of copper ions in water based on plasmon resonance transfer energy (Conference Presentation)," Proc. SPIE 10894, Plasmonics in Biology and Medicine XVI, 108940K (Presented at SPIE BiOS: February 04, 2019; Published: 4 March 2019); https://doi.org/10.1117/12.2508520.6008594714001.
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