Chirality is essential in nature and often pivotal for biological information transfer, for example, via odor messenger molecules. While the human nose can distinguish the enantiomers of many chiral odors, the technical realization by an artificial sensor or an electronic nose, e‐nose, remains a challenge. Herein, we present an array of six sensors coated with nanoporous metal–organic framework (MOF) films of different homochiral and achiral structures, working as an enantioselective e‐nose. While the achiral‐MOF‐film sensors show identical responses for both isomers of one chiral odor molecule, the responses of the homochiral MOF films differ for different enantiomers. By machine learning algorithms, the combined array data allow the stereoselective identification of all compounds, here tested for five pairs of chiral odor molecules. We foresee the chiral‐MOF‐e‐nose, able to enantioselectively detect and discriminate chiral odors, to be a powerful approach towards advanced odor sensing.

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The electrochemical deposition of Co nanoparticles on carbon ionic liquid electrode (CILE) was described and further used as the platform to construct a myoglobin (Mb) electrochemical biosensor. CILE was prepared by mixing a certain ratio of carbon powder, 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF 4 ), and liquid paraffin together. The presence of ionic liquid on the electrode surface facilitated the formation of Co nanoparticles, and a layer of Co nanoparticles was deposited on the surface of CILE with the average diameter of 300 nm after the cyclic voltammetic scan in the CoCl 2 solution. The formed Co/CILE was used as a new basal electrode for the investigation on the direct electrochemistry of protein. Mb molecules were further cast on the surface of Co/CILE and immobilized with Nafion film. The fabricated Nafion/Mb/Co/CILE showed good electrochemical behaviors with a pair of well-defined quasi-reversible redox peaks of Mb obtained, which was attributed to the electrochemical reaction of heme Fe(III)/Fe(II) redox couples. The results indicated that the presence of Co nanoparticles exhibited great promotion to the direct electron transfer of Mb. The Mb electrochemical biosensor showed good electrocatalytic activity to the reduction of hydrogen peroxide and trichloroacetic acid (TCA). The modified electrodes showed good stability and reproducibility, which had potential application in third generation biosensor.

A sensor array with four identical photoresponsive azobenzene-containing metal–organic framework films is selectively irradiated. By photoprogamming the array, the sensor selectivity is switched and optimized.

Detection and recognition of volatile organic compounds (VOCs) are crucial in many applications. While pure VOCs can be detected by various sensors, the discrimination of VOCs in mixtures, especially of similar molecules, is hindered by crosssensitivities. Isomer identification in mixtures is even harder. Metal−organic frameworks (MOFs) with their well-defined, nanoporous, and versatile structures have the potential to improve the VOC sensing performance by tailoring the adsorption affinities. Here, we detect and identify ternary xylene isomer mixtures by using an array of six gravimetric, quartz crystal microbalance (QCM)-based sensors coated with selected MOF films with different isomer affinities. We use classical molecular simulations to provide insights into the sensing mechanism. In addition to the attractive interaction between the analytes and the MOF film, the isomer discrimination is caused by the rigid crystalline framework sterically controlling the access of the isomers to different adsorption sites in the MOFs. The sensor array has a very low limit of detection of 1 ppm for each pure isomer and allows the isomer discrimination in mixtures. At 100 ppm, 16 different ternary o−p−m-xylene mixtures were identified with high classification accuracy (96.5%). This work shows the unprecedented performance of MOF-sensor arrays, also referred to as MOF-electronic nose (MOF-enose), for sensing VOC mixtures. Based on the study, guidelines for detecting and discriminating complex mixtures of volatile molecules are also provided.