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Photoluminescent and gas-sensing properties of ZnO nanowires prepared by an ionic liquid assisted vapor transfer approach

Hierarchical SnO 2 fi bers assembled from wrinkled thin tubes are synthesized by controlling the microphase separation between tin precursors and polymers, by varying fl ow rates during electrospinning and a subsequent heat treatment. The inner and outer SnO 2 tubes have a number of elongated open pores ranging from 10 nm to 500 nm in length along the fi ber direction, enabling fast transport of gas molecules to the entire thin-walled sensing layers. These features admit exhaled gases such as acetone and toluene, which are markers used for the diagnosis of diabetes and lung cancer. The open tubular structures facilitated the uniform coating of catalytic Pt nanoparticles onto the inner SnO 2 layers. Highly porous SnO 2 fi bers synthesized at a high fl ow rate show fi ve-fold higher acetone responses than densely packed SnO 2 fi bers synthesized at a low fl ow rate. Interestingly, thin-wall assembled SnO 2 fi bers functionalized by Pt particles exhibit a dramatically shortened gas response time compared to that of un-doped SnO 2 fi bers, even at low acetone concentrations. Moreover, Pt-decorated SnO 2 fi bers signifi cantly enhance toluene response. These results demonstrate the novel and practical feasibility of thin-wall assembled metal oxide based breath sensors for the accurate diagnosis of diabetes and potential detection of lung cancer.

The humidity dependence of the gas‐sensing characteristics in SnO2‐based sensors, one of the greatest obstacles in gas‐sensor applications, is reduced to a negligible level by NiO doping. In a dry atmosphere, undoped hierarchical SnO2 nanostructures prepared by the self‐assembly of crystalline nanosheets show a high CO response and a rapid response speed. However, the gas response, response/recovery speeds, and resistance in air are deteriorated or changed significantly in a humid atmosphere. When hierarchical SnO2 nanostructures are doped with 0.64–1.27 wt% NiO, all of the gas‐sensing characteristics remain similar, even after changing the atmosphere from a dry to wet one. According to diffuse‐reflectance Fourier transform IR measurements, it is found that the most of the water‐driven species are predominantly absorbed not by the SnO2 but by the NiO, and thus the electrochemical interaction between the humidity and the SnO2 sensor surface is totally blocked. NiO‐doped hierarchical SnO2 sensors exhibit an exceptionally fast response speed (1.6 s), a fast recovery speed (2.8 s) and a superior gas response (Ra/Rg = 2.8 at 50 ppm CO (Ra: resistance in air, Rg: resistance in gas)) even in a 25% r.h. atmosphere. The doping of hierarchical SnO2 nanostructures with NiO is a very‐promising approach to reduce the dependence of the gas‐sensing characteristics on humidity without sacrificing the high gas response, the ultrafast response and the ultrafast recovery.

Accumulated evidence has established that aberrant regulation of histone deacetylases (HDACs) is one of the major causes of the development of human malignancies. Among different iso-enzymes of HDAC and sirtuins grouped as the HDAC super family, little is known as to how histone deacetylase 2 (HDAC2) causes carcinogenesis in solid tumors. Here, in order to investigate the possible role of HDAC2 in gastric carcinogenesis, we analyzed the expression of HDAC2 in 71 gastric adenocarcinomas by immunohistochemistry. Moderate to strong expression of HDAC2 was found in 44 (62%) out of a total of 71 tumors. The majority of positive tumors, which were detected in the nucleus but not in normal gastric epithelium, did not express HDAC2 or showed only weak positive staining. Interestingly, we also noted that HDAC2 expression appeared to be associated with tumor aggressiveness as HDAC2 expression was observed to be statistically significant in advanced gastric cancer (P=0.0023, Chi-square test) and in positive lymph node metastasis (P=0.0713, Chi-square test). Taken together, these results suggest that HDAC2 may play an important role in the aggressiveness of gastric cancer.

We fabricated a nanowire-based gas sensor using a simple method of growing SnO(2) nanowires bridging the gap between two pre-patterned Au catalysts, in which the electrical contacts to the nanowires are self-assembled during the synthesis of the nanowires. The gas sensing capability of this network-structured gas sensor was demonstrated using a diluted NO(2). The sensitivity, as a function of temperature, was highest at 200 °C and was determined to be 18 and 180 when the NO(2) concentration was 0.5 and 5 ppm, respectively. Our sensor showed higher sensitivity compared to different types of sensors including SnO(2) powder-based thin films, SnO(2) coating on carbon nanotubes or single/multiple SnO(2) nanobelts. The enhanced sensitivity was attributed to the additional modulation of the sensor resistance due to the potential barrier at nanowire/nanowire junctions as well as the surface depletion region of each nanowire.

The selective detection of two different gases, NO(2) and C(2)H(5)OH, has been achieved using a p-type Co(3)O(4)-decorated n-type ZnO nanowire (NW) network sensor. The gas selectivity was explained by the catalytic effect of nanocrystalline Co(3)O(4) and the extension of the electron depletion layer via the formation of p-n junctions.