Planar waveguide enzyme sensors coated with nanocomposite membranes for water pollution monitoring.

Attenuated total reflection (ATR) of light in a SiO[2]/Si[3]N[4] planar waveguide was successfully exploited with a view to developing a highly sensitive enzyme sensor for monitoring typically agricultural and industrial water pollutants. The Si[3]N[4] surface of the waveguide sensing window was coated with nanocomposite polyelectrolyte selfassembled (PESA) membranes containing cyclotetrachromotropylene (CTCT) indicator and enzymes. The reaction of three enzymes namely urease, acetylcholine esterase or butyrylcholine esterase was accompanied by changes in pH, varying the absorption coefficient of the CTCT indicator.An experimental set-up of a single channel enzyme sensor was constructed to investigate the capability of the planar waveguide to register small changes in the light absorption of the PESA membrane. It was found that due to the multiple reflections phenomena, the sensitivity of a planar waveguide was higher than that for traditional absorption spectroscopy and previously reported waveguiding structures by at least three orders of magnitude. The respective enzyme reactions as well as their inhibition with toxic agents such as cadmium and lead ions were studied by in-situ monitoring the changes in output intensity of the planar waveguide. The results were remarkable, since traces of the above pollutants were detected with concentrations as low as to 1 ppb.The work was also extended to design and implement a laboratory scale enzyme sensor array. A multi-channel reaction cell and light guiding system were designed for this purpose. The analysis of the experimental results demonstrated that the multichannel enzyme sensor was able to produce adequate responses to the presence of different pollutants of industrial (cadmium, lead and nickel) and agricultural (imidacloprid, paraoxon and DVDP) origin, in the concentration range from 1 ppb to 1000 ppb. The distinct pattern of sensor responses was analysed by the implementation of artificial neural network algorithm. Despite a rather small amount of experimental data, the trained neural networks were able to classify and quantify the pollutants with an acceptable average error of 6.24 %

Synthesis of composite thin-film polymer consisting of tungsten and zinc oxide as hydrogen gas detector

A composite polymer consisting of polyaniline (PANI) was synthesised via oxidative polymerisation by varying concentrations of transitional metal oxides and the presence of a hydrogen dissociation catalyst, palladium (Pd). The metal oxides chosen for this study were tungsten oxide (WO3) and zinc oxide (ZnO). The composite polymer samples were characterised using Fourier transform infrared (FTIR) spectroscopy where ultraviolet-visible (UV-Vis) spectroscopy was used to observe the optical changes of the thin films due to exposure to hydrogen. The FTIR spectra obtained confirmed the synthesis of PANI composite. Based on the UV-VIS analysis, PANI-ZnO composite polymer showed the highest difference in peak intensity before and after exposure to hydrogen with 11.4% difference

Occupational safety and health assessment in metal industry within small and medium enterprise

According to annual report from the Social Security Organization (SOCSO) between years 2009 and 2011, metal industry has the highest reported number of accidents compared to the other manufacturing industry in small and medium enterprises (SMEs). Therefore, the aim of this study is to investigate the actual causes of problems that lead to the accidents involving metal industries within SMEs. In this study, checklist through site visits has been used to collect the data. The overall result reveals that the main causes of accident are due to organization failure, human factor, machine failure and surrounding environment

Planar waveguide enzyme sensors coated with nanocomposite membranes for water pollution monitoring

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Optical biodetection of cadmium and lead ions in water

A three layer waveguiding silicon dioxide (SiO2)/silicon nitride (Si3N4)/SiO2 structure on silicon substrate was proposed as an optically efficient biosensor for calibration of heavy metal ions in drinking water. The catalytic activities of urease and acetylcholine esterase (AchE) were inhibited by the presence of cadmium (Cd2+) and lead (Pb2+) ions. The detection limit as low as 1 ppb was achieved by employing the technique of total reflection at the interface between the Si3N4 core and composite polyelectrolyte self-assembled (PESA) membranes containing cyclotetrachromotropylene (CTCT) as an indicator