Humidity-Independent Artificial Olfactory Array Enabled by Hydrophobic Core–Shell Dye/MOFs@COFs Composites for Plant Disease Diagnosis

Abstract

As a class of important artificial olfactory system, the colorimetric sensor array possesses great potential for commercialization due to its cost-effectiveness and portability. However, when applied to practical applications, the humidity interference from ambient environment and dissatisfactory sensitivity for trace target VOCs are largely unsolved problems. To overcome the problems, we developed a series of dye/MOFs@COFs gas-sensing materials with core–shell structure using a hydrophobization strategy by encapsulation of dye/metal–organic frameworks (MOFs) into hydrophobic covalent organic frameworks (COFs). Benefiting from the hydrophobic property of the COF shell, the dye/MOFs@COFs composites were endowed with excellent humidity-resistance even under 100% relative humidity (RH). Moreover, due to the uniform distribution of dyes on the porous MOFs, the dye/MOFs@COFs sensors also exhibited improved sensitivity at the sub-ppm level, compared with conventional dye sensors. On basis of the excellent humidity-resistance and improved sensitivity, an artificial olfactory array based on dye/MOFs@COFs composites was proven to be a successful practical application in early and accurate detection of wheat scab (1 day after inoculation) by monitoring its released VOC markers. The synthetic strategy for core–shell dye/MOFs@COFs is applicable to a wide range of colorimetric sensor arrays, endowing them with excellent humidity-resistance and sensitivity for the feasibility of practical applications.

Covalent–Organic Framework (COF)‐Core–Shell Composites: Classification, Synthesis, Properties, and Applications

“…Reproduced with permission. [ 168 ] Copyright 2022, American Chemical Society. g) Construction and principle of electrochemical sensors.…”

“…To address this issue, Wang's group synthesized a hybrid dye/MOFs@COFs material with significantly improved performance and used it for the practical monitoring of VOCs. [ 168 ] Specifically, first, the dye was uniformly distributed in the apertures on the MOFs, which ensured a much better sensitivity of the sensor; second, the composite material after loading with the TPB‐DVA‐COF shell exhibited excellent hydrophobic properties with a water contact angle of 120°, much higher than the 15° of dye@UiO (Figure 19d). The moisture resistance was further judged by the Euclidean distance (ED).…”

“…d) Water contact angle, e) ED value, and f) color difference profile to 1-octen-3-ol with different concentrations of dye, dye/UiO, and dye/UiO@TPB-DVA-3. Reproduced with permission [168]. Copyright 2022, American Chemical Society.…”

Biomimetic Metal–Organic Framework-Based Photonic Crystal Sensor for Highly Sensitive Visual Detection and Effective Discrimination of Benzene Vapor

“…Heretofore, some studies have focused on adding new functional materials to PCs to detect VOCs, such as functional polymers, − biomass materials, graphene, inorganic materials, − and metal–organic frameworks (MOFs) . Among them, MOFs, which are formed by metals and organic ligands, have been paid much attention due to their adjustable and porous structures. − Currently, the sensing detection platform derived from MOFs has gradually entered the public’s vision. − However, the MOF-based PC sensors usually show the problems of insufficient color saturation and poor optical conversion performance to realize colorimetric gas sensing. Moreover, the interaction mechanism between the PC sensors and VOC gases, as well as the influence of composition materials on the detection results, has long been a shortcoming in the research process.…”

Colorimetric Aerogel Gas Sensor with High Sensitivity and Stability

“…Metal–organic frameworks (MOFs) as an ideal carrier have been demonstrated to improve the reliability and sensitivity of gas sensors for detecting volatile organic compounds (VOCs). For instance, MOF-based colorimetric sensors, optical sensors, and electrical sensors have been developed to improve detection sensitivity due to the microporous channels of MOFs decreasing the diffusion rate to enhance the adsorption efficiency of gaseous molecules . Much effort has been devoted to achieving the sensitive detection of VOCs through colorimetric gas sensors. – However, the high mobility of airflow poses a greater challenge for the intake of air volume and the reaction probability of gaseous molecules on solid sensors.…”