Solubilization of Multiwall Carbon Nanotubes by 3-Aminopropyltriethoxysilane Towards the Fabrication of Electrochemical Biosensors with Promoted Electron Transfer

A simple procedure has been described for the fabrication of multi-wall carbon nanotube (CNT) based electrochemical sensors. 3-Aminopropyltriethoxysilane (APTES) induced solubilization of CNTs allowed for the modification of electrode surfaces. With glucose oxidase (GOx), a flavin (FAD) containing enzyme as a model system, APTES was used as a solubilizing agent for CNTs as well as an immobilization matrix for GOx to construct a mediatorless biosensor. Our biosensor was able to efficiently monitor direct electroactivity of GOx at the electrode surface. A well-defined glucose response was observed at -0.45 V (vs. Ag/AgCl) whereas relevant physiological levels (0.1 mM) of three common interfering species, uric acid, ascorbic acid, and acetaminophen, resulted in no response. Although CNTs modified by APTES acted as semiconductors to reduce the exposed sensing surface, we reasoned 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 FAD site and facilitated direct electron transfer to the immobilized enzyme. The glucose biosensor prepared using a carbon fiber (11 μm) exhibited picoamperometric current response within 5 s with detection limits of 5-10 μM.