Facile Fabrication of Ultrathin Metal-Organic Framework-Coated Mono layer Colloidal Crystals for Highly Efficient Vapor Sensing

The sorption properties and structural versatility of metal organic frameworks (MOFs) make them superior chemical sensing materials with both high sensitivity and selectivity, but the fabrication of MOF sensors with optimized performances still remains a major challenge. Herein, we propose a simple yet powerful optical sensing motif based on ultrathin MOF-coated monolayer colloidal crystals (MCCs), which allows for high efficiency in vapor sensing through changes in their effective refractive index (RI). Two optical modes exist in this sensor, namely, photonic eigenmodes and Fabry-Perot oscillations, both of which can be used as the signal transducer. Selective response to a series of alcohols, water, and acetonitrile was exhibited, reflecting well the characteristic sorption properties of the integrated MOF, with which colorimetric reporting was readily achieved. Linear response to a broad dynamic range of vapor concentration was realized. The sensitivity was found to depend closely on the thickness of the MOP coating and can be further enhanced accordingly. Ultrafast response time (<5 s) and excellent recyclability were also demonstrated. These substantial improvements in performance are attributed to the efficacy of signal transduction and the enhanced pore accessibility and diffusion efficiency, which are intrinsically endowed by the optical motif design. Our findings should provide new insights into the design and fabrication of MOP sensors toward real-world applications.