Multiwall carbon nanotube (MWCNT) based electrochemical biosensors for mediatorless detection of putrescine

γ-Aminopropyltriethoxysilane (APTES)-induced solubilization of multi-wall carbon nanotube CNTs allowed for the modification of electrode surfaces. APTES also served as an immobilization matrix for putrescine oxidase (POx) to construct an amperometric biosensor. Although CNTs modified by APTES acted as semiconductors to reduce the exposed sensing surface, we reasoned that nanoscale "dendrites" of CNTS modified by APTES formed a network and projected outwards from the electrode surface and acted like bundled ultra-microelectrodes that allowed access to the active site and facilitated direct electron transfer to the immobilized enzyme. Our biosensor was able to efficiently monitor direct electroactivity of POx at the electrode surface. The putrescine biosensor prepared using the modified glassy carbon electrode exhibited current response within 10 s with a detection limit of 500 nM.