Chemosensors, Volume 4, Issue 1 (March 2016) – 5 articles

Two different classes of fluorescent dyes were prepared as a turn off/on sensor system for aldehydes. Amino derivatives of a boron dipyrromethene (BDP) fluorophore and a xanthene-derived fluorophore (rosamine) were prepared. Model compounds of their product with an aldehyde were prepared using salicylaldehyde. Both amino boron dipyrromethene and rosamine derivatives are almost non-fluorescent in polar and apolar solvent. However, imine formation with salicylaldehyde on each fluorophore increases the fluorescence quantum yield by almost a factor of 10 (from 0.05 to 0.4). These fluorophores are therefore suitable candidates for development of fluorescence-based sensors for aldehydes. Full article

This article presents a review of recent research efforts and developments for the fabrication of metal-oxide gas sensors using chemical vapour deposition (CVD), presenting its potential advantages as a materials synthesis technique for gas sensors along with a discussion of their sensing performance. Thin films typically have poorer gas sensing performance compared to traditional screen printed equivalents, attributed to reduced porosity, but the ability to integrate materials directly with the sensor platform provides important process benefits compared to competing synthetic techniques. We conclude that these advantages are likely to drive increased interest in the use of CVD for gas sensor materials over the next decade, whilst the ability to manipulate deposition conditions to alter microstructure can help mitigate the potentially reduced performance in thin films, hence the current prospects for use of CVD in this field look excellent. Full article

A composite metal oxide semiconductor (MOS) sensor array based on tin dioxide (SNO₂) and zinc oxide (ZnO) has been fabricated using a straight forward mechanical mixing method. The array was characterized using X-ray photoelectron spectroscopy, scanning electron microscopy, Raman spectroscopy and X-ray diffraction. The array was evaluated against a number of environmentally important reducing and oxidizing gases across a range of operating temperatures (300–500 °C). The highest response achieved was against 100 ppm ethanol by the 50 wt% ZnO–50 wt% SnO₂ device, which exhibited a response of 109.1, a 4.5-fold increase with respect to the pure SnO₂ counterpart (which displayed a response of 24.4) and a 12.3-fold enhancement with respect to the pure ZnO counterpart (which was associated with a response of 8.9), towards the same concentration of the analyte. Cross sensitivity studies were also carried out against a variety of reducing gases at an operating temperature of 300 °C. The sensors array showed selectivity towards ethanol. The enhanced behaviour of the mixed oxide materials was influenced by junction effects, composition, the packing structure and the device microstructure. The results show that it is possible to tune the sensitivity and selectivity of a composite sensor, through a simple change in the composition of the composite. Full article

Several technologies are available for decreasing nitrogen oxide (NOx) emissions from combustion sources, including selective catalytic reduction methods. In this process, ammonia reacts with nitric oxide (NO) and nitrogen dioxide (NO2). As the stoichiometry of the two reactions is different, electrochemical sensor systems that can distinguish between NO and NO2 in a mixture of these two gases are of interest. Since NO and NO2 can be brought to equilibrium, depending on the temperature and the surfaces that they are in contact with, the detection of NO and NO2 independently is a difficult problem and has not been solved to date. In this study, we explore a high surface area sonochemically prepared CuO as the resistive sensing medium. CuO is a poor catalyst for NOx equilibration, and requires temperatures of 500 C to bring about equilibration. Thus, at 300 C, NO and NO2 retain their levels after interaction with CuO surface. In addition, NO adsorbs more strongly on the CuO over NO2. Using these two concepts, we can detect NO with minimal interference from NO2, if the latter gas concentration does not exceed 20% in a NOx mixture over a range of 100–800 ppm. Since this range constitutes most of the range of total NOx concentrations in diesel and other lean burn engines, this sensor should find application in selective detection of NO in this combustion application. A limitation of this sensor is the interference with CO, but with combustion in excess air, this problem should be alleviated. Full article