Reagentless carbon paste phosphate biosensors: preliminary studies

The development of a reagentless phosphate biosensor with potential applications in continuous monitoring of environmental samples is described. The sensor is based on a biorecognition sequence of three enzymes: phosphorylase A, phosphoglucomutase and glucose 6-phosphate dehydrogenase. The incorporation of these enzymes, the substrate glycogen, the cofactor NAD(+), and Os(1,10-phenanthroline-5,6-dione)(2)Cl-2 mediator in a carbon paste electrode covered with in situ formed hydrogels was the fundamental base for the development of an amperometric enzyme electrode for the detection of inorganic phosphate. A study of the effects on the response of enzymatic cofactors, and the operating conditions and the optimisation of the biosensor response were carried out with dialysis membrane-covered glassy carbon electrodes, achieving a maximum current density of 2 mu A cm(-2) a detection limit of 6 mu M of phosphate with an extended linear dynamic range up to 2 mM, and sensitivity in the linear region of 4.5 mu A cm(-2) mM(-1) with a useful pH operational range between 6.5 and 7.5. The preliminary results with carbon paste phosphate electrodes showed a maximum current density of 30 mu A cm(-2), a detection limit of 2 mM of phosphate with linearity up to 250 mM, and sensitivity in the linear region of 0.1 mu A cm(-2) mM(-1). (C) 1998 Elsevier Science S.A. All rights reserved.