Tandem MOF-Based Photonic Crystals for Enhanced Analyte-Specific Optical Detection

Owing to their structural variability, metal–organic frameworks (MOFs) lend themselves well as chemical sensing materials by providing both high sensitivity and selectivity. Here, we integrate different types of MOFs (ZIF-8, HKUST-1, CAU-1-NH2) into photonic multilayers referred to as Bragg stacks (BSs), which report on adsorption events through changes in their effective refractive index (RI). The fabrication of photonic multilayers is accomplished by spin-coating colloidal suspensions of MOF nanoparticles and/or the high RI-material TiO2. While their incorporation in BSs allows for the label-free readout of host–guest interactions, the choice of particular types of MOFs determines the sensing properties of the BS. Here, we present MOF-based BSs with enhanced specificity toward molecular analytes by combining two different MOFs in a single platform. The sensing performance of our BSs is demonstrated by a combined spectroscopic and principal component analysis of their vapor response. Time-dependent measurements reveal fast response times and good recoverability of the multilayers. Moreover, we demonstrate that combinatorial sensing is feasible by arranging different MOF BSs in a basic color pattern, which highlights the potential of MOF-based multilayers in arrayed sensor devices.