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Miniaturization technology is of great importance in the research field of gas sensors. By using MEMS (micro-electro-mechanical system) technology, various micro-sensors have been developed. To fabricate chemiresistive type micro-sensors, one of the critical technologies lies in that the sensing material is needed to precisely load onto the designated micro-region, which is still a difficult task up to now. Herein, patterned self-assembly monolayer (SAM) with super-hydrophobic characteristic, which is prior grown onto the non-sensing region of the micro-chip, is used to guide the sensing material spontaneously flow onto the hydrophilic sensing area. As a proof of concept, Pd nanodots modified mesoporous-In 2 O 3 is successfully loaded onto the desired micro-sensing area of a micro heating-plate sensor. The fabricated sensor shows ultra-high response to H 2 gas with concentrations in the range of 0.5–100 ppm. Without SAM, some special instruments such as micro-manipulator are needed to deposit the sensing material onto the micro-sensing region. Our experiments indicate that the patterned SAM not only simplify the process of material loading, but also facilitates to improve the sensing performance (i.e. reduce the noise coming from sensing material dispersion and electric leakage). Our technology is suitable for various sensing materials precisely loading onto micro sensors without the aid of special instruments. [ABSTRACT FROM AUTHOR]

High-performance catalysts are crucial for many applications, including high-performance gas sensors. However, the catalysts used in gas sensors need to be screened through many experimental measurements, which is time-consuming and labor-intensive. Herein, the catalytic activity of ZSM-5 zeolites with different Si/Al ratios is quantitatively evaluated using a resonant microcantilever that enables in-situ temperature-programmed desorption (cantilever-TPD) measurements. Since the frequency shift obtained by the cantilever-TPD measurement is proportional to the number of probe molecules, the cantilever-TPD experiment can successfully measure the number of active sites and desorption activation energy of the catalyst. Therefore, the cantilever-TPD experiment quantitatively characterizes the catalytic activity through the comprehensive analysis of the number of active sites and the desorption activation energy, eliminating the need for the traditional trial-and-error method to study the gas-sensing performance. According to the test results of cantilever-TPD, the ZSM-5 zeolite with satisfactory performance is preferred as the catalytic material, and the ZnO/ZSM-5 double-layer sensor is made to detect trace amounts of the greenhouse gas Freon R134a. The gas sensing results show that the optimized ZSM-5 sensor has good sensitivity, limit of detection (LOD), repeatability, and selectivity, fully confirming the evaluation results of the cantilever-TPD. • Resonant microcantilever is used for TPD measurements of catalytic-induced sensing materials. • The catalytic activity of ZSM-5 zeolites with different Si/Al ratios has been quantitatively evaluated. • ZSM-5 zeolite, with satisfactory performance, was selected as the catalytic-induced sensing material. [ABSTRACT FROM AUTHOR]

SO 2 sensor is highly demanded in the application fields such as environmental protection and food manufactory. Herein, an integrated microsensor is developed for SO 2 gas detection. For the fabrication of microsensor, ZnO nanosheets sensing material is firstly loaded onto the sensing area of the microsensor by using inkjet printing technology. Then, Al 2 O 3 loaded with Ru nanoparticles (Ru/Al 2 O 3 ) as catalyst are locally deposited onto the surface of ZnO nanosheets layer. Gas sensing performance measurements indicate that the fabricated microsensor exhibits a selective response to SO 2 , and a good linear relationship in the range of 5–115 ppm SO 2 gases. Besides, this integrated microsensor has short response and recovery time. On-line mass spectrometry (on-line MS) experiment further reveals the formation of sulfur monoxide (SO ) radical as an intermediate product for SO 2 sensing. During the sensing process, Ru/Al 2 O 3 as catalyst layer brings SO 2 molecules to be broken down into easily detectable species (i.e. SO ), and then ZnO nanosheets with abundant gas transport channels capture the produced SO generating output signals. Therefore, this kind of sensing material configuration exploits the advantage of each element, and makes it possible for trace and selective detection of SO 2 gas. [ABSTRACT FROM AUTHOR]

Freon R134a is a widely used refrigerant that can cause a severe greenhouse effect and should be detected on site. However, it is a big challenge for semiconductor gas sensors to detect the inert Freon R134a molecules. Herein, mesoporous γ-Al 2 O 3 is synthesized and loaded on top of ZnO sensing materials to form a bilayer microsensor to realize high-performance detection of Freon R134a. The mesoporous γ-Al 2 O 3 material first decomposes the inert R134a molecule into a large number of active radicals. The generated reactive radicals are then easily sensed by the ZnO material. The limit of detection (LOD) of the bilayer sensor reaches the ppm level, which meets the requirements for on-site detection of Freon R134a leakage. The online mass spectrum (online MS) is used to identify the produced radicals qualitatively. According to the online MS results, the catalytic mechanism of mesoporous γ-Al 2 O 3 for Freon R134a molecules has been clearly revealed. • Mesoporous γ-Al 2 O 3 is synthesized for the detection of Freon R134a. • Micro-hotplates are manufactured using MEMS technology. • The MEMS microsensor shows mW-level power consumption. • Mesoporous γ-Al 2 O 3 has good catalytic activity for Freon molecules. • Mass spectrometry (MS) techniques are used to reveal the sensing mechanism. [ABSTRACT FROM AUTHOR]