Table 1 summarizes the application of MOS and metal-organic frameworks (MOFs) materials to gas sensors. Although the method based on GC is accurate, it is costly, not easy to miniaturize, and involves a complicated sampling process. The nondispersive infrared gas sensor also has the shortcomings of high-test cost, long test cycle, and not easy to miniaturize. Therefore, it is necessary to study a new type of gas sensor, which can not only be miniaturized but also run at room temperature to reduce power consumption.Capacitive gas sensor as an electrical sensor achieves the sensing effect by changing the dielectric constant [4][5][6] or dielectric layer thickness [7] after absorbing the target molecule. The capacitance value of a capacitive sensor is generally independent of the electrode material, and some materials with a lower temperature coefficient can be selected as the electrode, so its temperature stability is superb. At the same time, capacitive sensors have the advantages of simple structure, easy manufacturing, high measurement accuracy, and miniaturization. [8][9][10][11] Therefore, capacitive sensors have fantastic advantages when applied to gas sensing. The materials used in capacitive gas sensors mainly include zeolites, [12,13] metal oxides, [14] and carbon nanotubes, [15] but some shortcomings including high working temperature, high cost, and difficult process also limit their further development. [16,17] Therefore, a material with higher selectivity is needed for capacitive gas sensors.MOFs are an emerging class of microporous/mesoporous crystal material that assembled by metal ions/clusters and organic ligands through coordination bonds. MOFs materials have ultrahigh porosity, large surface-to-volume ratio and flexible skeleton, widely explored in gas storage, [18,19] separation, [20] catalysis, [21,22] magnetism, [23] and sensor. [24,25] According to the different structures of MOF materials, it can be divided into the following categories: MIL series, ZIF series, UiO series, HKUST series, IRMOF series, and PCN series, etc. Among them, the MIL series, ZIF series, and UiO series are widely used in the field of gas sensing.The MIL series mainly composed of transition metals (Cr, Fe, V) or lanthanide metals, and the ligands are mainly dicarboxylic acids (terephthalic acid, succinic acid). The MIL series generally have excellent stability and ultra-high specific surface area, which has a positive effect on gas adsorption and sensing. The ZIF series has a 3D network structure similar to zeolite, Gas sensors have been widely used in detection of industrial gas leak, air quality detection, and medical diagnosis. Although some chemical sensors have been commercialized, there are still some challenges such as sensitivity, cycle stability, and high power consumption. Metal-organic frameworks (MOFs) have high specific surface area, rich porosity, and excellent reversible/selective adsorption ability for various gases. Therefore, MOFs has been considered as an ideal sensing material. Metal active sites and...

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The fabrication of gas sensors with flexible properties and sensitive performances is of great importance for improving wearable sensing electronics. Herein, we coated a metal-organic framework (UiO-66-NH 2 ) on flexible electrospun polyvinylidenefluoride (PVDF) nanofibers as sensing layer for real-time monitoring of toxic SO 2 at room temperature. The developed capacitive sensor possesses a great bending flexibility, excellent cycling stability, high detection sensitivity, light weight as well as portable ability. The fabricated sensor possesses a short response time with 435 s and 185 s towards 150 ppm and 1 ppm, respectively. Importantly, the flexible sensor still maintained outstanding sensing behavior with the retention value of 98.4% in the detection of SO 2 at 10 ppm after bending 2000 times. In addition, significant cycling performance was desirably achieved, and the response value of the sensor was also kept at about 88.7% towards 50 ppm SO 2 , compared with original sensor after 20 days. This strategy can provide promising applications for the development of wearable devices for the detection of harmful gases.