Nadarajah Karuppiah

Chitosan-based tyrosinase optical phenol biosensor employing hybrid nafion/sol-gel silicate for MBTH immobilization.

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.

An Optical Biosensor based on Immobilization of Laccase and MBTH in Stacked Films for the Detection of Catechol

The fabrication of an optical biosensor by using stacked films where 3-methyl-2-benzothiazolinone hydrazone (MBTH) was immobilized in a hybrid nafion/sol-gel silicate film and laccase in a chitosan film for the detection of phenolic compounds was described. Quinone and/or phenoxy radical product from the enzymatic oxidation of phenolic compounds was allowed to couple with MBTH to form a colored azo-dye product for spectrophometric detection. The biosensor demonstrated a linear response to catechol concentration range of 0.5-8.0 mM with detection limit of 0.33 mM and response time of 10 min. The reproducibility of the fabricated biosensor was good with RSD value of 5.3 % (n = 8) and stable for at least 2 months. The use of the hybrid materials of nafion/sol-gel silicate to immobilize laccase has altered the selectivity of the enzyme to various phenolic compounds such as catechol, guaicol, o-cresol and m-cresol when compared to the non-immobilized enzyme. When immobilized in this hybrid film, the biosensor response only to catechol and not other phenolic compounds investigated. Immobilization in this hybrid material has enable the biosensor to be more selective to catechol compared with the non-immobilized enzyme. This shows that by a careful selection of different immobilization matrices, the selectivity of an enzyme can be modified to yield a biosensor with good selectivity towards certain targeted analytes.

Biosensor based on glutamate dehydrogenase immobilized in chitosan for the determination of ammonium in water samples

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 beta-nicotinamide adenine dinucleotide (NADH) oxidation in the presence of alpha-ketoglutaric acid at a wavelength of 340 nm. The biosensor showed optimum activity at pH 8. The optimum chitosan concentrations and enzyme loading were found to be at 2% (w/v) and 0.08 mg, respectively. Optimum concentrations of NADH and alpha-ketoglutaric acid both were obtained at 0.15 mM. A linear response of the biosensor was obtained in the ammonium concentration range of 0.005 to 0.5 mM with a detection limit of 0.005 mM. 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 1 month when stored dry at 4 degrees C.

Poly(hydroxyl ethyl methacrylate) hydrogel matrix for phenol biosensor

This paper discusscs the use of poly(hydroxy1 ethyl methacrylate). @oly(HEMA)) hydmgel as a mamx for tyrosinase hmobilization in a biosensor for the detection of phenolic compounds. A two-electrode system, i.e. a combination of working electrode and a Ag/AgCI (3M KCI) reference electrode was used for the consrm~tion of the biosensor. Screen primed electrodes were used as working electrodes for these smdy. The responses of the biosensor containing poly(HEM.4) membranes with tyrosinase immobilized towards phenol, catechol and m-cresol werc ~xamined.

Fabrication of an optical biosensor based on immobilized MBTH and tyrosinase for determination of phenolic compounds

Fabrication of biosensor for phenolic compounds determination employing optical method is described. The biosensor involved bi-layer which consist of immobilized 3-methyl-2-benzothiazolinone hydrazone (MBTH) in composite nafion/sol-gel silicate film and immobilized tyrosinase in chitosan film. The enzymatic oxidation product of phenolic compounds were stabilized through the formation of adduct with MBTH which can be monitored spectrophotometrically at wavelength of 490 run. The fabricated biosensor gave a linear response towards phenol, catechol and m-cresol in the concentration range of 5.0-74.0 /spl mu/M, 5.0-91.0 /spl mu/M, 9.0-120.0 /spl mu/M with detection limit of 1.9, 2.1, 4.0 /spl mu/M, respectively. The biosensor was stable for a duration of at least 3 months.