FIELD OF THE INVENTION
 This invention is in the field of bioelectronics and it relates generally to biosensors useful for measuring the concentration and/or the presence of organic analytes in liquid medium, e.g. medium of environmental, industrial, or clinical origin.
 In the following description reference will be made to several prior art documents shown in the list of references below. The reference will be made by indicating in brackets their number from the list.
 1. Wiliner I. and Katz E., Angew. Chem. Int. Ed., 2000, 39, 1180-1218.
 2. (a) Schuhmann, W.; Ohara, T. J.; Schmidt, H. L.; Heller, A. J.Am. Chem. Soc, 1991,113,1394-1397. (b) Wiliner, I.; Riklin, A.; Shoham, B.; Rivenzon, D.; Katz, E. Adv. Mater., 1993, 5, 912-915.
 3. (a) Heller, A. /. Phys. Chem. 1992, 96, 35793587. (b) Wiliner, I.; Wiliner, B. React. Polym. 1994, 22, 267-279.
 4. Katz E., Wiliner I., Kotlyar A. B., /. Electroanalytical Chem. 1999, 479, 64-68.
 5. (a) Bardea, A.; Katz, E.; Bdckman, A. R; Wiliner, I. /. Amer. Chem. Soc. 1997, 119, 9114-9119. (b) Katz, E.; Heleg-Shabtai, V.; Bardea, A.; Wiliner, I.; Rau H. K.; Hechnel, W., Biosens. Bioelectron. 1998, 13, 741-756.
BACKGROUND OF THE INVENTION
 A basic feature of a bioelectronic device is the immobilization of a biomaterial onto a conductive or semiconductive support, and the electronic transduction of the biological functions associated with the biological substrates.
 A biosensor is an analytical device incorporating biological and chemical sensing elements, either intimately connected to or integrated with a suitable transducer, which enables the conversion of concentrations of specific chemicals into electronic signals. A majority of biosensors produced thus far have incorporated enzymes as biological sensing elements (1). The electronic transduction of the enzyme-substrate interactions may also provide an analytical means to detect a respective substrate. The chemical means to assembly the enzymes on conductive or semiconductive supports include the immobilization thereof on a substrate by means of self-assembling monolayers or thin films, polymer layers, membranes, carbon paste or sol-gel materials.
 A specific class of enzymes which have been proposed for the use in analytical biochemical methods are redox enzymes. A redox reaction involves the transfer of electrons from the enzyme to the analyte—in a reduction reaction, or from the analyte to the enzyme in an oxidation reaction. If there is an electrical communication between the redox center of the enzyme molecules and the electrode material, there is an electrical charge flow which can serve
as an indication of the presence of the analyte and the extent of charge flow may serve to measure the analyte's concentration. Alternatively, the determination may be based on the measurement of a product of the reaction by non-electrochemical means, e.g. by HPLC.
 The direct electron transfer between the enzyme redox center and the electrode is limited, since the redox center is sterically insulated by the protein matrices. Consequently, the electrical communication between the redox enzymes and the electrodes may be established by an electron mediator group, often also termed "electron relay" (2), or by immobilizing the redox-proteins in electroactive polymers (3).
 One of the attractive applications of bioelectrocatalytic electrodes is the development of biofuel cell assemblies. The biofuel cell utilizes biocatalysts for the conversion of chemical energy into electrical energy. Many organic substrates undergo combustion in oxygen or are oxidized with the release of energy. Methanol and glucose are abundant raw materials that can be used as biofuels which undergo oxidation, and molecular oxygen or hydrogen peroxide can act as the oxidizer.
 For example, in a classical fuel cell where methanol is used as the fuel, the electro-oxidation of methanol at the anode can be represented by:
 and the electro-reduction of oxygen at the cathode can be represented by:
 Protons generated at the anode are transported to the cathode. A flow of current is sustained by a flow of ions through the membrane separating the cell into cathodic and anodic compartments and a flow of electrons through the external load.
 An example of a biofuel cell assembly based on the bioelectrocatalytic oxidation of glucose by 02 (4) is showed schematically in FIG. 1. The cell consists of two electrodes, where the anode is functionalized by a surface-reconstituted glucose oxidase (GOx) monolayer and the cathode is modified with an integrated biocatalytic construction composed of cytochrome c (Cyt c) and cytochrome oxidase (COx). At the GOx monolayer-functionalyzed electrode, bioelectrocatalyzed oxidation of glucose to gluconic acid occurs, whereas at the Cyt c/COx layered electrode the reduction of 02 to water takes place. The GOx layer is generated by the reconstitution of apo-GOx (GOx without its FAD cofactor) on amino-FAD covalently linked to a pyrroloquinolino quinone (PQQ) monolayer. The PQQ unit acts as an electron transfer mediator that bridges between the anode and the enzyme redox center.
 A different approach to assemble biofuel cells is based on the bioelectrocatalyzed oxidation of 1,4-dihydronicotineamide cofactors. Various substrates, for example alcohols, hydroxy acids or sugars undergo biocatalyzed oxidation by enzymes dependent on the NAD(P)30 cofactor (5).
 The electrochemical, particularly amperometric biosensors, known in the art are powered by an external power source. This power source is used to apply external voltage to the electrodes and, thus, to polarize the electrodes and to provide electron transfer reactions.