A biomimetic sensor for the determination of extracellular O2− using synthesized Mn-TPAA on TiO2 nanoneedle film

By immobilizing synthesized Mn-TPAA (TPAA = tris[2-[N-(2-pyridylmethyl) amino] ethyl] amine) on TiO2 nanoneedle surface, a biosensor for superoxide ion (O2−) has been developed and applied for determination of O2− released from living cells. Direct electron transfer of Mn-TPAA is realized with a formal redox potential (E°′) falling in the range of the E°′ values of the redox couples O2/O2− and O2−/H2O2. This suggests that Mn-TPAA on TiO2 films is electrochemically active and capable of thermodynamically mediating both the oxidation of O2− to O2 and the reduction of O2− to H2O2. Therefore, Mn-TPAA immobilized on the TiO2 films can be used electrochemically for determination of O2− due to its electrochemical activities and biomimetic catalytic activities like superoxide dismutase (SOD) toward O2−. The present biomimetic O2− sensor shows high selectivity at the low working potential of 0 V vs. Ag|AgCl, a wide linear range from 10−7 M to 10−4 M and a quick response time within 6 s. By taking advantage of the developed method and the properties of biomimetic SOD themselves, we have realized the real-time monitoring of O2− concentration released from living cells and investigated the relationship between the concentration changes of O2− and intracelluar Ca2+, which may gain additional insights on the reactive oxygen species (ROS) signal transduction and other physiological and pathological events.