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Highlights • A simple process to fabricate flexible and highly sensitive mechanical sensors based on RGO/synergetic fiber bundles with various sensing functions including stretching, pressing, bending, vibration and torsion. • The mechanical sensor exhibited a high sensitivity (GF = −8.9), low limit of detection (0.05%) and wide sensing range (up to 75%) for tensile strain. • The sensor can be employed to detect full-range human actions from subtle physiological signals e.g. phonation, respiration, and real-time pulse wave to human physical activities e.g. finger joint bending, typing or grasping. • Large-area sensor arrays are successfully fabricated to spatially map pressure stimuli. Abstract We propose a flexible, multifunctional and highly sensitive mechanical sensor that can monitor various mechanical strains induced via stretching, pressing, bending, vibration and torsion. The sensor demonstrates a well-designed conductive fiber alignment based on synergetic fiber bundles coated with a thin reduced graphene oxide (RGO) layer (SF/RGO). When stretched, the fiber bundles fracture into gaps, islands, and bundles bridging the gaps; thus, allowing the conductive fiber bundles to serve as mechanical sensors capable of detecting trace tensile strain down to 0.05% with a high sensitivity (Gauge Factor = −8.9). Furthermore, the sensor also demonstrated high durability, wide sensing range (75% for strain, and 36 kPa for pressure). These remarkable features endow our sensing devices to monitor full-range human motions from subtle bio-signals e.g. pulse wave, phonation and respiration to human physical actions e.g. finger typing, bending or grasping. Furthermore, large-area sensor arrays are successfully fabricated to spatially map pressure stimuli, demonstrating great potential for applications in wearable electronics and healthcare. [ABSTRACT FROM AUTHOR]

Abstract: A high quality-factor (Q-factor) in-plane-mode resonant cantilever sensor is developed for real-time bio/chemical detection in liquids. With electrothermal excitation and piezoresistive frequency read-out integrated, the proposed sensor is realized by micromachining technology. The in-plane mode cantilever resonator can substantially decrease the liquid drag force, comparing to conventional out-of-plane resonance-mode cantilever, thereby, having achieved a much higher Q-factor of 249 when the cantilever is connected with a phase-lock-loop (PLL) interface circuit in water. After the mass sensitivity is calibrated by specifically binding streptavidin-labeled Dynabeads with the biotin-immobilized cantilever in phosphate buffered saline (PBS) solution, specific-antibody immobilized cantilevers have been used in real-time detection of Escherichia coli in PBS solution. Real-time detection of Hg2+ ions in aqueous Hg(NO3)2 is also carried out by using sensing-group-modified cantilevers, resulting in a finer noise-limited resolution than 100ppb. [Copyright &y& Elsevier]

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]

Searching for suitable materials for NO 2 sensing has important scientific significance and application value. First-principles calculations have been performed on the adsorption of NO 2 and its various interfering gases on the pristine C 3 N monolayer (p-C 3 N) and the B-doped C 3 N monolayer. The studies on the adsorption stability, geometric structure, charge transfer, and electronic structure indicate that the p-C 3 N is a promising room-temperature NO 2 sensor, with high selectivity and sensitivity, and good reversibility. For the B-doped C 3 N monolayer, the calculated formation energies suggest that B doping into the C 3 N lattice is thermodynamically highly favorable. Furthermore, B doping by replacing the N atom in the C 3 N monolayer should can further improve the sensing selectivity and sensitivity of the C 3 N monolayer toward NO 2 . However, it is noted that a large adsorption energy for NO 2 indicates that the B-doped C 3 N monolayer may be reversibly operated above the room temperature. The possible reason for the distinct adsorption behaviors of the various molecules is also provided. Our theoretical studies indicate the great potential of the C 3 N-based two-dimensional semiconductor as good NO 2 gas sensors. [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]

For the first time, ultrasensitive detection of 10 ppb CO has been realized using metal organic framework (MOF) crystals of Ni-MOF-74 as gravimetric-type sensing material with resonant microcantilever sensors. Due to the specific interaction between CO molecules and the active transitional metal centers of Ni 2+ in the Ni-MOF-74 crystal, the Ni-MOF-74 material with ultra-high surface area and nanoporous structure possesses large absorption capacity to CO gas. By loading the Ni-MOF-74 material onto the resonant microcantilever, the formed gravimetric sensor exhibits high-performance sensing to CO at trace level. The experimentally obtained limit of detection (LOD) of the sensor to CO reaches finer than 10 ppb (parts per billion in volume), which indicates an extremely high CO-detection sensitivity of the sensor. Besides the excellent sensitivity, the sensor also shows remarkable repeatability and long-term stability. Eight kinds of interfering gases are tested and a fine selectivity of the sensor is verified. This work indicates that MOF materials such as Ni-MOF-74 are promising in gravimetric-type gas sensing applications. [ABSTRACT FROM AUTHOR]

High performance NH 3 sensor is of great importance in various application fields such as environmental protection and early diagnosis of stomach cancer. Herein, carboxyl group functionalized mesoporous silica nanoparticles (C-MSNs) with ultrahigh specific surface area are developed as high performance mass-type sensing material for trace-level NH 3 detection. By using inkjet printing technology, C-MSNs material is precisely loaded on our lab-made integrated resonant microcantilever to construct a mass-type gas sensor. Based on the specific acid-base interaction between Brønsted acidic C-MSNs material and basic NH 3 molecules, our sensor exhibits satisfactory NH 3 sensing performance. The experimentally observed detection limit of our sensor reaches parts per billion (ppb) level. Exposed to NH 3 with identical concentration, our sensor outputs a higher response in wet air than that of in dry atmosphere. In real air, hydrate NH 3 molecule ( i.e. NH 3 · x H 2 O) has a larger molecular weight than anhydrous NH 3 in absolute dry experimental atmosphere. Therefore, our gravimetric sensor exhibits a higher response in real air. In order to in-depth elucidate the humidity-enhanced sensing effect, the micro-gravimetric sensing data obtained in wet air and in dry experimental environment are compared together. Based on our quantitatively measurement data, the molecular formula of hydrate NH 3 · x H 2 O existing in wet air (with 50–80% relative humidity) can be obtained as NH 3 ·2∼2.4H 2 O. [ABSTRACT FROM AUTHOR]

Aromatic amine such as aniline is one kind of carcinogenic substances that needs to be detected at low concentration. To sense trace level aniline, high performance sensing material is of great importance. Herein, metal organic framework of Zn 4 O(1,4-benzenedicarboxylate) 3 (commonly abbreviated as MOF-5) with abundant hierarchical nanopores is firstly employed as mass-type sensing material for low concentration aniline detection. By using one typical micro-gravimetric transducer of resonant microcantilever, the aniline-adsorbing induced mass-addition of MOF-5 is transformed to the detectible sensing signal of frequency shift. Based on resonant microcantilever with mass resolution of 1.5 pg/Hz, the fabricated sensor exhibits good sensitivity for aniline detection. The limit of detection is better than 1.4 ppm, and the selectivity is satisfactory to nine kinds of common interfering gases. The three-cycle repeatability of the sensor is also investigated with a relative standard deviation (RSD) of 4%. After 20 days, the sensor only shows a negligible response degradation which represents a good reproducibility. Materials Studio simulation results manifest that 1,4-benzenedicarboxylic ligand in MOF-5 crystals is the preferential site for aniline molecules adsorbing. [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]

Presented is nano-size effect of ZnO nanowires (NWs) on sensitivity of hydrogen sulfide (H 2 S) detection in ambient atmosphere. The sensing mechanism of ZnO NWs for H 2 S detection is found coming from nano-size effect that governs both the sulfuration reaction when H 2 S is introduced and the following desulfuration reaction when the gas is removed from air. Based on the nano-material property of smaller dimension featuring higher chemical-activity at surface, the sensitivity of ZnO NWs to ultra-low concentration H 2 S is expected to be increased by shrinking the NW diameter. In our experiment, suspended micro hotplates for chemiresistive sensing are fabricated to investigate the nano-size sensing effect. Besides conventional ZnO NWs with the diameter as 50 nm, a novel tree-branched nano-structure of ZnO NWs (with the branch diameter as 20 nm) is in situ grown onto the sensing-area of the micro hotplate. In order to investigate the sensing effect, both the 20 nm NW sensor and the 50 nm NW sensor are used to experimentally detect H 2 S with concentrations in the range of ppb - ppm . The 20 nm ZnO-NWs sensor realizes resoluble sensing to 5 ppb H 2 S, while the 50 nm sensor can only response to H 2 S with concentration higher than 50 ppb. The well validated nano-size effect of thinner NWs featuring higher sensing response can be extended for various chemical sensing nano-materials. [ABSTRACT FROM AUTHOR]

Increasing the aspect ratio of the microchannels of microfabricated gas chromatographic columns (μGCCs) can allow analytes to quickly reach equilibrium between the stationary phase and mobile phase, which helps improve their separation performance. In this paper, an all-silicon microfabricated gas chromatographic column (AS-μGCC) with a high aspect ratio was proposed and fabricated using deep reactive-ion etching (DRIE) and silicon direct bonding. Two AS-μGCCs with the lengths of 2 m and the aspect ratios of 6.6 (100 µm-width × 660 µm-depth) and 25 (30 µm-width × 750 µm-depth) were successfully fabricated. The effects of different aspect ratios on the column efficiency of AS-μGCCs were studied. A separation experiment showed that the column efficiency of the AS-μGCC with an aspect ratio of 25 (AS-μGCC-25) was 12 times higher than that of the AS-μGCC with an aspect ratio of 6.6 (AS-μGCC-6.6). The column efficiency of the AS-μGCC-25 was 1961 plates/m, and a heavy hydrocarbon mixture (C8–C20) could be separated using AS-μGCC-25 within 4.5 min [Display omitted] • Two all-silicon microfabricated gas chromatographic columns with aspect ratios of 25 and 6.6 were fabricated. • The AS-μGCC-25 showed a 12-fold improvement in the column efficiency as compared to the AS-μGCC-6.6. • By optimizing the conditions of the temperature programming, C8–C20 could be separated using AS-μGCC-25 within 4.5 min. [ABSTRACT FROM AUTHOR]

The redox homeostasis between glutathione (GSH) and peroxynitrite (ONOO-) is essential for maintaining normal physiological functions in biological system, and the imbalance of GSH and ONOO- is closely related to the pathogenesis of diverse diseases. Herein, we presented a dual-fluorophore and dual-site probe for the simultaneous detection of mitochondrial GSH and ONOO- via the integrated mechanism of ICT and FRET. The probe exhibited favorable response performance toward GSH and ONOO- at pH 7.4 including high sensitivity, fast response and superior selectivity. Especially, there was no interfering fluorescent signals of ONOO- (or GSH) during the detection of GSH (or ONOO-) alone, while significant fluorescence variation was observed during detecting ONOO- (or GSH) in the presence of GSH (or ONOO-). Therefore, the probe could monitor the coexistence of GSH and ONOO- not just the separate existence of GSH or ONOO-. Given these advantages, Mito-CM-CD has been successfully utilized for real-time visualization of GSH and ONOO- in normal HepG2 cells and drug-induced HepG2 cells. Importantly, it has been found that depletion of GSH and indirect formation of ONOO- are associated with the APAP-induced liver injury which can be effectively relieved by supplementing GSH. We anticipated that this research will promote to understand the interrelation of GSH and ONOO- under different physiological and pathological settings. [Display omitted] • Mito-CM-CD exhibited rapid response, high selectivity and low LOD to ONOO- and GSH. • The probe displayed quenched signal to ONOO- but enhanced signal to GSH at 640 nm under single-wavelength excitation. • Mito-CM-CD could sense ONOO- (or GSH) with enhanced blue but decreased red fluorescence in the presence of GSH (or ONOO-). • Confocal microscopy experiments indicated that Mito-CM-CD can be used for visualizing GSH and ONOO- in living cells. [ABSTRACT FROM AUTHOR]

In order to develop a volume fabrication route for chemical sensors, hydrogen-bond acidic hyper-branched polymer is synthesized and directly self-assembled in-batch onto MEMS resonant micro-cantilevers as sensing layer. The batch self-assembly is via a facile coupling reaction between the SH group in the self-assembled monolayer (SAM) and one OH group in the hyper-branched polymer. During the self-assembly process of the hyper-branched polymer, the polyurethane-industry used isophorone diisocyanate (IPDI) is employed as the key coupling reagent, since the two N C O coupling groups in IPDI feature different reactivity. The N C O group with higher reactivity is firstly reacted with the SH group pre-grown at the cantilever surface. Then, another N C O group with lower reactivity reacts with one OH group in the hyper-branched polymer. In this way the hydrogen-bond acidic hyper-branch polymer can be batch grafted onto a run of micro-cantilevers for uniform sensing to targeted gas. Through this route, the resonant cantilever gas sensors can be batch produced for uniform detection of trace organophosphates (OPs). Based on the specific interaction between the OH sensing group and the P O group in OP, the targeted molecules can be captured by the hyper-branched sensing polymer, and the mass addition induced frequency shift of the resonant cantilever is output as sensing signal. Sensing experiment is implemented for the sensors taken from one fabrication batch, resulting in satisfactory consistency in sensing performance. Taking 5 sensors as example, the deviation of the sensing response to 2 ppm dimethyl methylphosphonate (DMMP) is less than 1%. Besides, the sensor shows good repeatability/selectivity and good linear response to various concentrations (300 ppb to 1.5 ppm) of DMMP. [ABSTRACT FROM AUTHOR]

Abstract: Thiol-functionalized SBA-15 mesoporous silica materials with various pore sizes and specific surface areas were prepared by using a post-grafting process. All the obtained materials were characterized by SAXS, FT-IR, TGA, TEM and N2 adsorption isotherms. By using these functionalized mesoporous silica as sensing materials, the QCM sensor was constructed and used for detecting heavy metal ions. The experimental results indicated that the QCM sensor can detect 1ppm Hg2+ with the response frequency of 175Hz in the response time of 1min. The influence of response time, the amount of thiol groups, pore size and specific surface area of SBA-15 mesoporous silica on Hg2+ detection was studied systematically in this paper. [Copyright &y& Elsevier]

• A non-enzymatic electrochemical sensor was fabricated for the detection of free bilirubin in human serum. • The sensor can directly detect the free bilirubin without any sample labeling or pre-preparation. • The ceria nanocubes showed high catalytical ability and stability. • The detection linear range is up to 100 μM, the LOD is 0.1 μM in buffer solution, 1 μM in human serum sample, respectively. • The sample consumption is extremely small (5 μL), which may reduce the blood collecting pain of patients. Free bilirubin level is a significant indicator for the diagnosis of jaundice related diseases. Herein, ceria nanocubes are synthesized as catalyst for the direct electrochemical sensor of free bilirubin. The sensor is fabricated by simply modifying screen-printed electrodes with ceria nanocubes and carbon blacks. Owing to the catalytical activity of ceria nanocubes and conductivity of carbon blacks, this sensor can detect free bilirubin with high sensitivity and selectivity in a short response time. Under the optimized condition, the current of DPV peak is proportional to the bilirubin concentration up to 100 μM, with a LOD of 0.1 μM in phosphate buffer and 1 μM in human serum sample. The non-enzymatic sensor also shows good reproducibility and stability at room temperature. Moreover, only 5 μL test sample is required, the small sample consumption may facilitate the blood collection procedure. The sensor could be a potential candidate device for the point of care testing on free bilirubin in clinic. [ABSTRACT FROM AUTHOR]

• The top silicon of the SOI substrate was used as the thermistor's supporting layer. • The dead volume of the μTCD was as small as about 200 nL. • The detection level of the μTCD was as low as 5 ppm. In this paper, a micro thermal conductivity detector (TCD) with suspended thermistors based on a Silicon-On-Insulator (SOI) substrate was successfully fabricated by using a MEMS technique. The top layer of silicon of the SOI substrate was utilized as the supporting layer of the thermistor, which possessed excellent mechanical strength. The buried SiO 2 was utilized as the etch stop layer of deep reactive ion etching in the thermistor release process, which precisely defined the channels with a high depth-to-width ratio and acquired an ultra-small dead volume (∼200 nL). The micro TCD showed sensitive detection at levels as low as 5 ppm of n-alkanes C14-C16 mixtures. Besides, the micro TCD demonstrated excellent universal detection to gas mixtures, which detected all thirteen analytes in the standard sample of n-alkanes C8-C20 mixtures and all eight analytes in the standard sample of VOCs (volatile organic compounds). [ABSTRACT FROM AUTHOR]