Carbon based nanomaterials such as carbon nanotube (CNT) and carbon nanofiber (CNF) [1] have been studied for application to fuel cells,capacitors and various biosensors.We have greatly improved the direct electron transfer (DET) of enzymes on a sputtered nanocarbon film [2] or CNF modified carbon film electrode by employing the one-step UV/ozone treatment of these carbon materials.This treatment changed the CNF surface from hydrophobic to hydrophilic because a sufficient quantity of oxygen-containing functional groups was introduced onto the CNF surface.Furthermore,this simple and mild approach increased both the effective surface area and the number of edge-plane defect sites.As a result,the reversibility of redox species such as ferrocyanide and dopamine (DA) was greatly improved on the treated CNF modified electrode surface.We employed the treated CNF for enzymes modified electrode and obtained the highly efficient DET of bilirubin oxidase (BOD),cytochrome c (cyt c),and cytochrome P450 (CYP).For example,the oxygen reduction current of BOD on the treated CNF modified electrode was about 38 times higher than that on an untreated CNF-modified electrode.A treated CNF electrode modified with cyt c also exhibited a more than 6 times higher peak current [3].These results indicate that the combination of nanostructured carbon and a simple UV/ozone treatment process can efficiently create a functionalized surface for the electron transfer of enzymes,which provides an excellent opportunity for the development of new generations of enzyme based biosensor such as drug metabolism sensors through CYP.