A biomimetic sensor for the determination of extracellular O ₂ ^- using synthesized Mn-TPAA on TiO ₂ nanoneedle film

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