Correct choice is (b) ENFET
To elaborate: In the above diagram, ENFET is represented. ENFET means enzyme-linked field effect transistors. The main body of the biosensor is a p-type silicon chip with two n-type silicon areas. The chip is insulated by a thin layer of silica which forms the gate of the FET. Above the gate, there is an equally thin layer of H^+-sensitive material, a protective ion selective membrane, the biocatalyst and the analyte solution, which is separated by an inert encapsulating polyimide photopolymer. When a potential is applied between the electrodes, a current flows through the FET dependent upon the positive potential detected at the ion-selective gate and its consequent attraction of electrons into the depletion layer.