MICRO-ENZYME SENSORS WITH OSMIUMN COMPLEX AS MEDIATOR FOR L-AMINO ACIDS AND D-AMINO ACIDS

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Micro-enzyme sensors using L-amino-acid oxidase (EC 1.4.3.2) and D-amino-acid oxidase (EC 1.4.3.3) were developed for measuring L- and D-amino acids. The platinum micro-sensors (platinum diameter, 30 mum) were etched in hot aqua regia to create a cavity at their tip. A porous composite material prepared from acetylene black and Teflon emulsion was packed into the tip of the platinum micro-sensors and the redox mediator [Os (bpy)_3 ] (PF_6)_2 was monitored by cyclic voltammetry in the potential range 200-900 mV.The micro-sensors were dipped overnight in buffer solution containing the desired enzyme to immobilize in on the tip by adsorption method. Calibration curves for measurements of L- and D-amino acids, the effects of pH,temperature, and concomitant compounds, the life-time of the micro-sensors, and their availability for measuring L-amino acids in urine were examined. Under optimal conditions, the response of sensors was linear in the concentration ranges of 3.3-240mg/l L-amino acids and 0.83-17mg/l D-amino acids.