A DNA construct consisting of a nucleic acid template, (1), on which a nucleic acid-modified glucose oxidase (GOx), (3), was hybridized by cooperative bridging of the T-Hg2+-T units, and a nucleic acid-functionalized ferrocene, (5), was directly hybridized on a Au electrode. The resulting nanostructure revealed bioelectrocatalytic activities, where the ferrocene units mediated electron transfer between the redox center of the enzyme and the electrode. The bioelectrocatalytic functions of the system are regulated by the concentration of Hg2+ ions, which controls the content of the enzyme associated with the DNA template by means of the T-Hg2+-T bridging units. This phenomenon allowed the amperometric detection of He ions at a detection limit 1 x 10(-10) M with impressive selectivity.