Abstract: The present invention discloses an assay for nucleic acid which comprises the steps of;(a) providing a probe material comprising;(i) a sequence of nucleic acids complementary to a given target sequence and,(ii) a first ligand chemically linked thereto and capable of a specific binding reaction with an antiligand;(b) contacting the said probe material with an assay system comprising:(i) a suitable mediator, enzyme, substrate system capable of transferring charge to an electrode surface when the enzyme is catalytically active, and;(ii) a second ligand chemically linked to one of said mediator, enzyme or substrate, wherein the second ligand is capable of a competitive binding reaction with the antiligand, and;(iii) the said antiligand, Whereby the said first ligand competes with the said second ligand in a specific binding reaction with the antiligand, and;(c) contacting the above system with a solution suspected of containing the said target sequence whereby the binding of any of the said target sequence presen