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New acrylic microspheres were synthesised by photopolymerisation where the succinimide functional group was incorporated during the microsphere preparation. An optical biosensor for urea based on reflectance transduction with a large linear response range to urea was successfully developed using this material. The biosensor utilized succinimide-modified acrylic microspheres immobilized with a Nile blue chromoionophore (ETH 5294) for optical detection and urease enzyme was immobilized on the surface of the microspheres via the succinimide groups. No leaching of the enzyme or chromoionophore was observed. Hydrolysis of the urea by urease changes the pH and leads to a color change of the immobilized chromoionophore. When the color change was monitored by reflectance spectrophotometry, the linear response range of the biosensor to urea was from 0.01 to 1,000 mM (R2 = 0.97) with a limit of detection of 9.97 μM. The biosensor response showed good reproducibility (relative standard deviation = 1.43%, n = 5) with no interference by major cations such as Na+, K+, NH4+ and Mg2+. The use of reflectance as a transduction method led to a large linear response range that is better than that of many urea biosensors based on other optical transduction methods. [ABSTRACT FROM AUTHOR]

Abstract: An optical biosensor based on glutamate dehydrogenase (GLDH) immobilized in a chitosan film for the determination of ammonium in water samples is described. The biosensor film was deposited on a glass slide via a spin-coating method. The ammonium was measured based on β-nicotinamide adenine dinucleotide (NADH) oxidation in the presence of α-ketoglutaric acid at a wavelength of 340nm. The biosensor showed optimum activity at pH 8. The optimum chitosan concentrations and enzyme loading were found to be at 2% (w/v) and 0.08mg, respectively. Optimum concentrations of NADH and α-ketoglutaric acid both were obtained at 0.15mM. A linear response of the biosensor was obtained in the ammonium concentration range of 0.005 to 0.5mM with a detection limit of 0.005mM. The reproducibility of the biosensor was good, with an observed relative standard deviation of 5.9% (n =8). The biosensor was found to be stable for at least 1month when stored dry at 4°C. [Copyright &y& Elsevier]

Abstract: This paper presents artificial neural network (ANN)-based evaluation in signal processing of an optical phenolic biosensor. The biosensor was developed based on stacked immobilization of 3-methyl-2-benzothiazolinone hydrazone (MBTH) in hybrid Nafion/sol–gel silicate and tyrosinase in chitosan. The biosensor signal was simulated employing a feed-forward neural network with three layers and trained using back-propagation (BP) algorithm. Spectra generated from an optical phenolic biosensor at selected wavelengths were used as input data for ANN. The network architecture of 5 inputs neurons, 21 hidden neurons and 1 output neuron was found suitable for this application. The results show very good agreement between phenol concentration values obtained by using the developed biosensor and those predicted by ANN. [Copyright &y& Elsevier]

Abstract: The development of an optical biosensor based on immobilization of 3-methyl-2-benzothiazolinone hydrazone (MBTH) in hybrid nafion/sol–gel silicate film and tyrosinase in chitosan film for the detection of phenolic compounds has been described. Tyrosinase was immobilized in chitosan film deposited on the hybrid nafion/sol–gel silicate film containing MBTH. The enzymatic oxidation product of phenolic compounds were stabilized through formation of adduct with MBTH to produce a maroon color adduct. The color intensity of adduct was found to increase proportionally with the increase of the substrate concentrations after 5min exposure. The linearity of the biosensor towards phenol, catechol and m-cresol were in the respective concentration range of 0.5–7.0, 0.5–10.0 and 1.0–13.0mg/L with detection limit of 0.18, 0.23 and 0.43mg/L, respectively. The biosensor shows a good stability for at least 3 months. [Copyright &y& Elsevier]

Abstract: An optical biosensor based on the immobilized tyrosinase enzyme in a chitosan film is described for the detection of phenol. The film was prepared by depositing a chitosan solution containing tyrosinase onto a microscope glass slide via spin coating technique. The quinone produced from the enzymatic oxidation of phenol was reacted with 3-methyl-2-benzothiazolinone hydrazone (MBTH) to produce a maroon color adduct. The color intensity of the adduct was found to increase proportionally with the increase of the substrate concentrations after 15min exposure to the substrate. The optimum enzyme loading and chitosan concentrations were found to be 0.9mg and 2% (w/v), respectively. The biosensor also demonstrated optimum activity at pH 6–7, optimum temperature of 45°C and a linear response in the phenol concentration range of 2.5–70.0μM. The response characteristics of the biosensor towards different phenolic compounds were determined. It was found that the biosensor gave a linear response in the concentration range of 2.5–50.0μM for 4-chlorophenol, 2.5–100.0μM for m-cresol and 12.5–400.0μM for p-cresol. The limit of detection and the apparent Michaels–Menten constant (K m) of the biosensor were 0.9, 1.0, 1.0, 3.0μM and 0.038, 0.037, 0.056, 0.201mM for 4-chlorophenol, phenol, m-cresol and p-cresol, respectively. It showed good stability for at least 2 months. [Copyright &y& Elsevier]