Development of a disposable amperometric NH4+ biosensor based on a chemically modified screen-printed carbon electrode coated with glutamate dehydrogenase, 2-oxoglutarate, and NADH

摘要

A screen-printed carbon electrode (SPCE), impregnated with the electrocatalyst Meldola's Blue (MB), has been investigated as the base transducer in a disposable amperometric NH4+ biosensor; The MB-SPCE detects the cofactor NADH when it is polarized at a potential of only +0.05 V (vs. Ag/AgCl); electrocatalytic oxidation of the cofactor readily occurs at this potential. The device was converted into an NH4+ biosensor by coating the surface of the MB-SPCE with glutamate dehydrogenase, 2-oxoglutarate and NADH. When ammonium ions are present in the sample solution, a decrease in the anodic current occurs as a result of the enzymatic conversion of 2-oxoglutarate to glutamate which requires NADH. Chronoamperometry was performed on 40 mu L aliquots of solutions containing various concentrations of NH4+. A 30 s incubation period was used, then the potential was stepped from open circuit to +0.05 V (vs. Ag/AgCl); response currents were measured from the resulting chronoamperograms at a time of 120s (t(120s)). The detection limit was found to be about 2 mu M with biosensors containing 4.6 U of enzyme. The stability of these biosensors was examined after storage at 4 degrees C in a desiccator containing silica gel, the response was found to be constant for a period of about 29 days. The proposed biosensors were evaluated on samples of unspiked, and spiked river water; the recovery and precision data indicated that the devices could be expected to give reliable results for the low levers of NH4+ normaly expected in rivers. [References: 9]