Precise detection of heavy metal ions in water is of paramount importance owing to its detrimental effects on human health, especially with spectroscopically silent ions such as lead ions (Pb(II)). This study demonstrates the design and development of a novel portable and field-deployable fiber optic plasmonic absorption-based chemical sensor (PACS) for Pb(II) ion detection using a metal-organic framework (MOF-5) as a highly selective chemoreceptor. MOF-5 was grown in situ over the tannic acid-capped gold nanoparticles (AuNP, 20 nm) of the plasmonic U-bent fiber optic sensor (U-FOS) probes. The Pb(II) ion binding to MOF-5 was detected and quantified as an increase in the plasmonic absorption of the light by AuNP due to significant refractive index changes at the AuNP surface. Besides an excellent selectivity (Pb(II) vs. 11 potential interfering metal ions at 1:50 ppm), these sensors manifest a detection limit down to 0.5 ppb (20 times below the maximum contaminant level of 10 ppb), a wide dynamic range (0.5 ppb to 50 ppm). The sensor was challenged with filtered sewage samples (neat and spiked with 10 ppb) yielded recovery rates within 91% to 105% with respect to the standard ICP-MS analysis. With the notable merits of a facile and scalable probe fabrication process, long shelf-life (at least 12 weeks moisture-free storage), and simpler instrumentation (only with an LED-photodetector pair), the PACS/MOF-5 platform is highly promising for water quality measurements on-site.

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