Development of a Disposable Amperometric NH Biosensor Based on a Chemically Modified Screen-Printed Carbon Electrode Coated with Glutamate Dehydrogenase, 2-Oxoglutarate, and NADH

Abstract

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 NH 4 biosensor. The MB-SPCE detects the cofactor NADH when it is polarized at a potential of only 0.05 V (vs. AgaAgCl); electrocatalytic oxidation of the cofactor readily occurs at this potential. The device was converted into an NH 4 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 mL aliquots of solutions containing various concentrations of NH 4 . A 30 s incubation period was used, then the potential was stepped from open circuit to 0.05 V (vs. AgaAgCl); response currents were measured from the resulting chronoamperograms at a time of 120 s (t 120s ). The detection limit was found to be about 2 mM with biosensors containing 4.6 U of enzyme. The stability of these biosensors was examined after storage at 4 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 levels of NH 4 normaly expected in rivers.

Recent developments towards disposable screen-printed biosensors incorporating a carbon ink modified with the redox mediotor. Meldola's Blue

“…In addition, mass production using screen-printing technology allows fabrication at low cost; the biosensors could therefore be used once and discarded without the inherent problems of contamination. The prototype amperometric biosensor [16] was based on the following enzymatic reaction [17] where GLDH represents glutamate dehydrogenase. The measurement of NH 4 + was again dependent on the detection of NADH by its electrocatalytic oxidation at the MB-SPCE.…”

Selective and Rapid Biosensor Integrated into a Commercial Hand‐Held Instrument for the Measurement of Ammonium Ion in Sewage Effluent

“…In a previous study (Hart et al 1999), we reported on the development of a prototype amperometric biosensor for the measurement of NH 4 þ in river water at concentrations in the ppb range. In that study, the biosensor was used in conjunction with a standard laboratory-based potentiostat (Hart et al 1999).…”

“…In that study, the biosensor was used in conjunction with a standard laboratory-based potentiostat (Hart et al 1999). Although the device could be used to monitor levels in river water at the ppb level, this would not be appropriate for the higher levels present in sewage effluent i.e., above the K m ; therefore, the purpose of the present investigation was to further develop this system for such applications.…”

Chemometric analysis of screen-printed biosensor chronoamperometric responses

“…An usual procedure for sensor calibration consists in correlating a single point i t of the chronoamperogram with sample substrate concentration [10,14]. Nevertheless, the use of the overall chronoamperometric data is an alternative to improve the reliability of the assay.…”