The characteristics of a potentiometric biosensor for the determination of permethrin in treated wood based on immobilised cells of the fungus Lentinus sajor-caju on a potentiometric transducer are reported this paper. The potentiometric biosensor was prepared by immobilisation of the fungus in alginate gel deposited on a pH-sensitive transducer employing a photocurable acrylic matrix. The biosensor gave a good response in detecting permethrin over the range of 1.0-100.0 mu M. The slope of the calibration curve was 56.10 mV/decade with detection limit of 1.00 mu M. The relative standard deviation for the sensor reproducibility was 4.86%. The response time of the sensor was 5 min at optimum pH 8.0 with 1.00 mg/electrode of fungus L sajor-caju. The permethrin biosensor performance was compared with the conventional method for permethrin analysis using high performance liquid chromatography (HPLC), and the analytical results agreed well with the HPLC method (at 95% confidence limit). There was no interference from commonly used organophosphorus pesticides such as diazinon, parathion, paraoxon, and methyl parathion. (C) 2013 Elsevier B.V. All rights reserved.

A new silica-gel nanospheres (SiO(2)NPs) composition was formulated, followed by biochemical surface functionalization to examine its potential in urea biosensor development. The SiO(2)NPs were basically synthesized based on sol-gel chemistry using a modified Stober method. The SiO(2)NPs surfaces were modified with amine (-NH2) functional groups for urease immobilization in the presence of glutaric acid (GA) cross-linker. The chromoionophore pH-sensitive dye ETH 5294 was physically adsorbed on the functionalized SiO(2)NPs as pH transducer. The immobilized urease determined urea concentration reflectometrically based on the colour change of the immobilized chromoionophore as a result of the enzymatic hydrolysis of urea. The pH changes on the biosensor due to the catalytic enzyme reaction of immobilized urease were found to correlate with the urea concentrations over a linear response range of 50-500 mM (R-2 = 0.96) with a detection limit of 10 mM urea. The biosensor response time was 9 min with reproducibility of less than 10% relative standard deviation (RSD). This optical urea biosensor did not show interferences by Na+, K+, Mg2+ and NH4+ ions. The biosensor performance has been validated using urine samples in comparison with a non-enzymatic method based on the use of p-dimethylaminobenzaldehyde (DMAB) reagent and demonstrated a good correlation between the two different methods (R-2 = 0.996 and regression slope of 1.0307). The SiO(2)NPs-based reflectometric urea biosensor showed improved dynamic linear response range when compared to other nanoparticle-based optical urea biosensors.

One of the major problems in the analysis of ammonia (NH3) using spectrophotometric method is highly coloured water sample. A reflectometric NH3 sensor based on a facile single-step immobilisation of cobalt(II) (Co2+) ion onto high capacity Dowex HCR-W2 microspheres has been developed to enable the direct NH3 determination in highly coloured water samples. The combination of Co2+ ion-immobilised microspheres via cation exchange chemical reaction and reflectometric technique has improved the optode sensing performance with respect to linear response range and response time. Immobilised Co2+ ion, when complexed with NH3 gave a blue colouration of hexamminecobaltate(II) ([Co(NH3)(6)](2+)) complex at pH 13. The NH3 sensor reached maximum colour intensity in similar to 6 min at ambient conditions. The linear calibration curve was 60-290 mM NH3 with a detection limit of 16 mM NH3, which is suitable for direct determination of NH3-enriched leachate water samples. A good reproducibility between 5.4 and 5.9% relative standard deviation (RSD) was obtained with the probe and the sensing performance can be regenerated using buffer pH 1. The effect of potential interference ions has been investigated during the quantification of NH3 in heavily polluted sewage water. The results obtained were in good agreement with those produced by acidimetric reference method. Crown Copyright (C) 2012 Published by Elsevier B.V. All rights reserved.

A novel approach for the determination of Al3+ from aqueous samples was developed using an optode membrane produced by physical inclusion of Al3+ selective reagent, which is morin into a plasticized poly(vinyl chloride). The inclusion of Triton X-100 was found to be valuable and useful for enhancing the sorption of Al3+ ions from liquid phase into the membrane phase, thus increasing the intensity of optode's absorption. The optode showed a linear increase in the absorbance at lambda(max)= 425 nm over the concentration range of 1.85 x 10(-6)-1.1 x 10(-4) mol L-1 (0.05-3 mu g mL(-1)) of Al3+ ions in aqueous solution after 5 min. The limit of detection was determined to be 1.04 x 10(-6) mol L-1 (0.028 mu g mL(-1)). The optode developed in the present work was easily prepared and found to be stable, has good mechanical strength, sensitive and reusable. In addition, the optode was tested for Al3+ determination in lake water, river water and pharmaceutical samples, which the result was satisfactory. (C) 2015 Elsevier B.V. All rights reserved.

A regenerable electrochemical DNA biosensor based on a new type of acrylic microspheres and gold nanoparticles (AuNPs) composite coated onto a screen printed electrode (SPE) has been successfully developed for specific determination of the 35 S promoter from cauliflower mosaic virus (CaMV 35S) gene in soybean. DNA probe was immobilised onto acrylic microspheres via covalent bonding. The presence of modified gene in soybean can be detected via hybridisation of CaMV 35S gene-modified DNA with immobilised DNA probe, which was monitored by differential pulse voltammetry of anthraquinone-2sulfonic acid monohydrate sodium salt (AQMS) as redox indicator during hybridisation event. The peak current signal of AQMS was linearly related to the target CaMV 35S gene concentration over the range of 2 x 10(-15) to 2 x 10(-9) M (R-2 = 0.982) with a very low concentration detect limit (7.79 x 10(-16) M). The recovery test showed satisfactory results of 94.6 +/- 5.1-105.4 +/- 4.9% (n = 5) when the biosensor was used for the determination of genetically modified (GM) DNA sequences extracted from GM soybean samples. The DNA biosensor showed good reproducibility (relative standard deviation (RSD) below 5.0%, n = 5) and regenerability (RSD below 5.0%, n = 7). The biosensor response was stable up to 45 days of storage period at 4 degrees C. The main advantages of this biosensor design are very low detection limit and capability of reusing the biosensor for at least seven times after regeneration with mild sodium hydroxide. (c) 2013 The Authors. Published by Elsevier B. V. All rights reserved.

An amperometric electrochemical biosensor has been developed for ammonium (NH4+) ion detection by immobilising alanine dehydrogenase (AlaDH) enzyme in a photocurable methacrylic membrane made up of poly(2-hydroxyethyl methacrylate) (pHEMA) on a screen-printed carbon paste electrode (SPE). The current detected was based on the electrocatalytic oxidation of nicotinamide adenine dinucleotide reduced (NADH) that is proportional to the consumption of NH4+ ion whilst enzymatic amination of AlaDH and pyruvate is taking place. The biosensor was operated amperometrically at a potential of +0.6V and optimum pH 7. The NH4+ biosensor demonstrated linear response to NH4+ ion concentration in the range of 0.03-1.02 mg/L with a limit of detection (LOD) of 8.52 mu g/L. The proposed method has been successfully applied to the determination of NH4+ ion in river water samples without any pretreatment. The levels of possible interferents in the waters were negligible to cause any interference on the proposed method. The analytical performance of the biosensor was comparable to the colorimetric method using Nesslerisation but with much lower detection limit and linear response range at ppb level.

An optical fiber chemical sensor for the determination of free glutamate in food samples was fabricated based on the immobilization of 0.1 M copper(II) nitrate trihydrate onto sol-gel glass powder which was then mixed with methyl cellulose to form a pellet. A distinctive colour change from light blue to dark blue was observed in the presence of glutamate in less than 1 min. The colour change was measured by reflectance spectrophotometer at 691 nm. A linear relationship between the reflectance intensity and glutamate concentration was observed in the range of 12.5 to 500 mM with a limit of detection of 10.6 mM. This method is also reproducible with a relative standard deviation of less than 5%, no effect on pH of the glutamate solution and a good recovery of above 80%. The sensor was used for the determination of glutamate in common food items such as soups and flavor enhancers. The results obtained from the fabricated sensor were found to be comparable with HPLC method.

The fabrication of an optical biosensor based on stacked immobilisation of 3-methyl-2-benzothiazolinone hydrazone (MBTH) in sol-gel/butyl acrylate hybrid film and horseradish peroxidase (HRP) in chitosan film for capsaicin detection was studied. The optimum volume ratio of sol-gel to butyl acrylate was 1:0.5 (v/v). Peroxidase was immobilised in chitosan film deposited on top of the hybrid sol-gel/butyl acrylate film containing MBTH. The reaction between capsaicin and MBTH in the presence of HRP and hydrogen peroxide as oxidative agent was studied. The finding indicated that HRP catalysed the oxidative coupling reaction between MBTH and capsaicin thus producing red-coloured azo-dye compounds that could be observed at the wavelength of 505 nm. The colour intensity of the product was found to increase in proportion to the capsaicin concentration after 20-30 s of exposure. The linearity of the biosensor towards capsaicin was in the concentration range of 0.2-4.0 mM with detection limit of 0.17 mM. Relative standard deviation (RSD) values of reproducibility were 5.57-6.33%. The developed biosensor correlated well with the standard method, HPLC for the determination of capsaicin concentration in real samples. (C) 2013 Elsevier B.V. All rights reserved.

The complexation reaction of Co2+ (M) and the 1,1-diethyl-3-(4-methoxybenzoyl)thiourea (L) ligand in the binary mixtures: acetonitrile-dimethylsulfoxide (MeCN-DMSO), acetonitrile-dichloromethane (MeCN-DCM), water-dimethylsulfoxide (H2O-DMSO) and acetonitrile-water (MeCN-H2O), was investigated using a conductometric method at temperatures of (288.15, 298.15, 308.15 and 318.15) K. In all cases, the conductance data showed that the stoichiometry of the neutral complex formed between M and L is 1:3 [M:3L], which indicates that the Co2+ ion was oxidized to Co3+ during the reaction. The best estimate of the stability constant, log(10) K (f), = 3.31 for the [CoL3] complex, was observed with the MeCN-DCM (20:80 %) binary mixture at 298.15 K. The values of the thermodynamic parameters (i.e., and ) for the formation of the [CoL3] complex were obtained from the temperature dependence of the stability constant via van't Hoff plots. The results show that, in most cases, the [CoL3] complexes are enthalpy destabilized but entropy stabilized. The values and signs of the thermodynamic parameters are affected by the nature and composition of the mixed solvents but are independent of the temperature.

In the title compound, C14H18N2O2S, the piperidine ring has a chair conformation. Its mean plane is twisted with respect to the 4-methoxybenzoyl ring, with a dihedral angle of 63.0 (3)degrees. The central N-C(=S)-N(H)-C(=O) bridge is twisted with an N-C-N-C torsion angle of 74.8 (6)degrees. In the crystal, molecules are linked by N-H center dot center dot center dot O and C-H center dot center dot center dot O hydrogen bonds, forming chains along the c-axis direction. Adjacent chains are linked by C-H center dot center dot center dot pi interactions, forming layers parallel to the ac plane. The layers are linked by offset pi-pi interactions [intercentroid distance = 3.927 (3) angstrom], forming a supramolecular three-dimensional structure.

In the title compound, C13H16N2O2S, the pyrrolidine ring has a twisted conformation on the central CH2-CH2 bond. Its mean plane is inclined to the 4-methoxybenzoyl ring by 72.79 (15). In the crystal, molecules are linked by N-H center dot center dot center dot O and C-H center dot center dot center dot O hydrogen bonds to the same O-atom acceptor, forming chains along [001]. The chains are linked via slipped parallel pi-pi interactions [inter-centroid distance = 3.7578 (13) angstrom], forming undulating slabs parallel to (100).

The effect of surfactants on the Al(III)-morin complex have been studied. It was found that non-ionic surfactant noticeably enhances the absorbance of the Al(III)-morin complex. Determination of submicrogram quantities of Al(III) ion at pH4.00 was made possible by the addition of triton X-100. Maximum absorption was obtained at wavelength of 425 nm, with the calculated molar absorptivity, epsilon e, of 9.31 x 10(3) l. mol(-1). cm(-1). A linear calibration curve of 0.03 to 2.0 mu g mL(-1) with the detection limit of 0.015 mu g mL(-1) was attained for determination of Al(III) ion. The calculated relative standard deviation (r.s.d) was 2.2% for Al(III) ion quantified at 1.0 mu g mL(-1). The influence of foreign ions towards the Al(III)-morin complex responses have been carried out too, with Cu(II), Zn(II) and Pb(III) were found to be the main interferences.

The use of multilayer of gold nanoparticles (AuNPs) attached on gold electrode surface via thiol chemistry to fabricate an ammonium (NH4+) ion biosensor based on alanine dehydrogenase (AlaDH) was investigated. The approach of the study was based on construction of biosensor by direct deposition of AuNPs and 1,8-octanedithiol (C8-DT) onto the gold electrode surface. For the immobilisation of enzyme, 2-mercaptoethanol (2BME) was first covalently attached to AlaDH via esther bonding and then followed by chemically attached the 2BME-modified AlaDH (2BME-AlaDH) moiety onto the AuNPs electrode via the exposed thiol group of 2BME. The resulting biosensor response was examined by means of amperometry for the quantification of NH4+ ion. In the absence of enzyme attachment, the use of three layers of AuNPs was found to improve the electrochemistry of the gold electrode when compared with no AuNPs was coated. However, when more than three layers of AuNPs were coated, the electrode response deteriorated due to excessive deposition of C8-DT. When AlaDH was incoporated into the AuNPs modified electrode, a linear response to NH4+ ion over the concentration range of 0.1-0.5 mM with a detection limit of 0.01 mM was obtained. In the absence of AuNPs, the NH4+ ion biosensor did not exhibit any good linear response range although the current response was observed to be higher. This work demonstrated that the incorporation of AuNPs could lead to the detection of higher NH4+ ion concentration without the need of dilution for high NH4+ ion concentration samples with a rapid response time of < 1 min.

A new bioanalytical method for urea determination by using the immobilized urease on the highly luminescent ZnS quantum dots (QDs), which functioned as the pH fluorescent label has been developed. Bioconjugation of ZnS QDs to urease via amide bond was performed to obtain the ZnS QDs-urease bioconjugate. Upon enzymatic hydrolysis of urea by the immobilized urease, a pH change to a more alkaline condition has led to the deprotonation of ZnS QDs, and an increase in the fluorescence intensity can be observed. The fluorescence intensity of the urease conjugated ZnS QDs changed linearly with the urea concentrations between 4 x 10(-9) M and 4 x 10(-3) M (R-2 = 0.992) at pH 6 with a calibration sensitivity of 179.46 intensity/decade. No noticeable influence by the Ca2+, Mg2+, K+ and Na+ ions on the response of the fluorescent pH bioprobe. Urea determination in soil sample by using the urea bioprobe was in good agreement with the standard DMAB (p-dimethylaminobenzaldehyde) UV-vis spectrophotometric method. By employing the strategy of ZnS QDs-urease bioconjugation, the stable covalent link between the two substances has appeared to widen the dynamic range and lower the detection limit for urea compared to free enzyme and QDs in solution for bioassay of urea concentration. (C) 2016 Elsevier B.V. All rights reserved.

This paper reports the use of a polymer inclusion membranes (PIMs) for direct determination of Al(III) ions in natural water by using a fluorescence based optode. The best composition of the PIMs consisted of 60 wt.% (m/m) poly (vinyl chloride) (PVC) as the base polymer, 20 wt.% (m/m) triton X-100 as an extractant, 20 wt.% (m/m) dioctyl phthalate (DOP) as plasticizer and morin as the reagent, was used in this study. The inclusion of triton X-100 was used for enhancing the sorption of Al(III) ions from liquid phase into the membrane phase, thus increasing the optode fluorescence intensity. The optimized optode was characterized by a linear calibration curve in the range from 7.41 x 10(-7) to 1.00 x 10(-4) molL(-1) of Al(III), with a detection limit of 5.19 x 10(-7) molL(-1). The response of the optode was 4 min and reproducible results were obtained for eight different membranes demonstrated good membrane stability. The optode was applied to the determination of Al(III) in natural water samples. The result obtained is comparable to atomic absorption spectrometry method.

A highly sensitive and simple reagent immobilization procedure for a non-plasticized fluorescence optode based on polymer inclusion membranes (PIM) has been developed. The preparation procedure is based on physical immobilization procedure, namely encapsulation technique which produces an optical sensing membrane. The sensitive PIM contains poly (vinyl chloride) (PVC) as the base polymer, Aliquat 336 as an extractant and sodium morin-5-sulphonate (NaMSA) as the reagent. The use of PIM has increased the response of the PIM based optode about five-fold enhancement compared to the non-PIM optode. The optimized optode was characterized by a linear calibration curve in the range from 5.19 x 10(-7) to 6.00 x 10(-5) mol L-1 of aluminium(III) (Al(III)), with a detection limit of 4.07 x 10-7 mol L-1. The response of the optode was three minutes and it was also found to be reproducible. The optode has been successfully tested for the determination of Al(III) in natural water samples and result obtained is comparable to atomic absorption spectrometry method. (C) 2014 Elsevier B.V. All rights reserved.

1,2-bis-(N'-benzoylthioureido)cyclohexane (BTCH), C22H24N4O2S2, was successfully synthesized, characterized by infrared and NMR spectroscopic techniques and supported by X-ray structural studies. The compound was tested for the fabrication of a potentiometric sensor for Hg2+ metal ions. The sensor based on photocurable self-plasticizing poly(n-butylacrylate) membrane with immobilized BTCH as ionophore exhibits linear response in a Nernstian manner within the concentration range of 10(-5) - 0.1 M mercury ions. The sensor displays low detection limit with response time between 50 - 100 seconds. The electrode reveals a good selectivity for mercury ion over several other tested cations. (C) 2012 Published by Elsevier B. V. Selection and/or peer review under responsibility of Asia-Pacific Chemical, Biological & Environmental Engineering Society

An optical Al(III) sensor base on reflectance principle has been developed using polymer inclusion membranes (PIMs) beads. The immobilized PIMs beads are consists of poly(vinyl chloride) (PVC), Aliquat 336, dioctyl phthalate (DOP) and eriochrome cyanine R (ECR) reagent. The sensor which was based on immobilized PIMs beads produced higher response compared to sensor based on non-immobilized PIMs beads. The response time of the sensor was 3 min with an optimum pH value of 6.0. This optical Al(III) sensor gave a linear response at the range of 5.56x10(-5) - 3.52x10(-4) molL(-1), with the limit of detection value 3.41x10(-5) molL(-1). Validation of Al(III) value in spiked natural water samples by using Al(III) sensor developed in this study showed no significance differences compared with results obtained by using conventional atomic absorption spectrophotometer.

Background: A novel optical sensor for the rapid and direct determination of permethrin preservatives in treated wood was designed. The optical sensor was fabricated from the immobilisation of 2,6-dichloro-p-benzoquinone-4-chloroimide (Gibbs reagent) in nafion/sol-gel hybrid film and the mode of detection was based on absorption spectrophotometry. Physical entrapment was employed as a method of immobilisation. Results: The sensor gave a linear response range of permethrin between 2.56-383.00 mu M with detection limit of 2.5 mu M and demonstrated good repeatability with relative standard deviation (RSD) for 10 mu M at 5.3%, 100 mu M at 2.7%, and 200 mu M at 1.8%. The response time of the sensor was 40 s with an optimum response at pH 11. Conclusions: The sensor was useful for rapid screening of wood or treated wood products before detailed analysis using tedious procedure is performed. The validation study of the optical sensor against standard method HPLC successfully showed that the permethrin sensor tended to overestimate the permethrin concentration determined.