A glucose sensor for electrically determining blood glucose concentration for in vivo and in vitro applications and comprising an iridium substrate with an oxidized surface, to which is bonded a first film of silanized gamma propyltriethoxysilane and a second film of glucose oxidase covalently bonded thereto. The electrode provides an electrial signal, the amplitude of which varies in response to changes in blood glucose concentration, with the electrode being both rugged and stable.