Development of a disposable amperometric NH4+ biosensor based on a chemically modified screen-printed carbon electrode coated with glutamate dehydrogenase, 2-oxoglutarate, and NADH
Jp. Hart et al., Development of a disposable amperometric NH4+ biosensor based on a chemically modified screen-printed carbon electrode coated with glutamate dehydrogenase, 2-oxoglutarate, and NADH, ELECTROANAL, 11(6), 1999, pp. 406-411
A screen-printed carbon electrode (SPCE), impregnated with the electrocatal
yst Meldola's Blue (MB), has been investigated as the base transducer in a
disposable amperometric NH4+ biosensor; The MB-SPCE detects the cofactor NA
DH when it is polarized at a potential of only +0.05 V (vs. Ag/AgCl); elect
rocatalytic 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 ammoniu
m 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 glutam
ate which requires NADH. Chronoamperometry was performed on 40 mu L aliquot
s 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 chrono
amperograms at a time of 120s (t(120s)). The detection limit was found to b
e 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 unsp
iked, and spiked river water; the recovery and precision data indicated tha
t the devices could be expected to give reliable results for the low levers
of NH4+ normaly expected in rivers.