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

Abstract

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 × 10–4 (single-digit ppm VOC concentration) up to 0.06 are resolved with a resolution better than 1 × 10–5.

Vapor-Phase Loading of an Ionic Liquid into a Zeolitic Imidazolate Framework

“…The loading (ip/c) was calculated by assuming a unit cell volume of 4.924 nm 3 . Methanol adsorption isotherms of unloaded and IL-loaded films were measured using the iSE in combination with a stainless steel in situ gas cell and home-build vapor dosing equipment …”

“…40 Methanol adsorption isotherms of unloaded and IL-loaded films were measured using the iSE in combination with a stainless steel in situ gas cell and home-build vapor dosing equipment. 41 Synthesis of ZIF-8. Powder: Small Crystals.…”

Recent progress on MOF-based optical sensors for VOC sensing

“…Lately, Ameloot et al explored surface plasmon polariton (SPP) resonance by incorporating a ZIF-8 thin film via CVD approach onto an AlO x /Ag layered surface on a glass substrate for methanol detection. 121 The sample configuration is illustrated in Figure 14b. The signal of VOC uptake was transduced into SPP shifts by applying spectroscopic total internal reflection ellipsometry (TIRE).…”

“…Recently, Ameloot et al explored surface plasmon polariton (SPP) resonance by incorporating a ZIF-8 thin film via the CVD approach onto an AlO x /Ag layered surface on a glass substrate for methanol detection. 121 The sample configuration is illustrated in Fig. 14b .…”

“…(b) TIRE/SPP principle and TIRE measurement geometry with the sample layer stacks. (c) The measured SPP peak redshift in methanol compared to dry N 2 121.…”