Parts-per-Million Detection of Volatile Organic Compounds via Surface Plasmon Polaritons and Nanometer-Thick Metal-Organic Framework Films

Because of their guest adsorption properties, metal-organic frameworks (MOFs) are promising materials to realize chemical sensors. However, achieving high sensitivities requires the reproducible deposition of well-defined MOF films and their integration with a suitable sensor design. In this work, we report the sensitive detection of volatile organic compounds (VOCs) by transducing the adsorption in zeolitic imidazolate framework 8 (ZIF-8) thin films, prepared by chemical vapor deposition (MOF-CVD), into surface plasmon polariton (SPP) shifts measured via total internal reflection ellipsometry (TIRE). It is shown that defect formation during MOF-CVD alters the VOC uptake. However, SPP resonances tunable over the entire Vis-NIR range and as sharp as 14 nm are obtained for optimized synthesis conditions. Record-breaking shifts stronger than 150 nm upon methanol uptake and a limit of detection below 1 ppm are observed. By modeling the TIRE spectra, changes in the ZIF-8 refractive index from 1 x 10(-4) (single-digit ppm VOC concentration) up to 0.06 are resolved with a resolution better than 1 X 10(-5).