REAGENTLESS CARBON-PASTE PHOSPHATE BIOSENSORS - PRELIMINARY STUDIES

The development of a reagentless phosphate biosensor with potential ap plications in continuous monitoring of environmental samples is descri bed. The sensor is based on a biorecognition sequence of three enzymes : phosphorylase A, phosphoglucomutase and glucose 6-phosphate dehydrog enase. The incorporation of these enzymes, the substrate glycogen, the cofactor NAD(+), and Os(1,10-phenanthroline-5,6-dione)(2)Cl-2 mediato r in a carbon paste electrode covered with in situ formed hydrogels wa s the fundamental base for the development of an amperometric enzyme e lectrode for the detection of inorganic phosphate. A study of the effe cts on the response of enzymatic cofactors, and the operating conditio ns and the optimisation of the biosensor response were carried out wit h dialysis membrane-covered glassy carbon electrodes, achieving a maxi mum current density of 2 mu A cm(-2) a detection limit of 6 mu M of ph osphate with an extended linear dynamic range up to 2 mM, and sensitiv ity in the linear region of 4.5 mu A cm(-2) mM(-1) with a useful pH op erational range between 6.5 and 7.5. The preliminary results with carb on paste phosphate electrodes showed a maximum current density of 30 m u A cm(-2), a detection limit of 2 mM of phosphate with linearity up t o 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.