Distribution-enhanced direct electron communication of hemoglobin immobilized in pristine TiO2 nanotube arrays

In this work, efficient direct electron transfer (eT) has been achieved for hemoglobin (Hb) immobilized in pristine TiO2 nanotube arrays (TNAs) through controlling Hb distribution. Confocal laser scanning microscope (CLSM) and field emission scanning electron microscopy (FESEM) studies confirm that Hb is distributed inside the TiO2 nanopores in a nearly uniform monolayer. The peak-to-peak separation (Delta E-p) is measured as 57 mV and the apparent heterogeneous eT rate constant (k(s)) is calculated as 1.365 s(-1), both superior to that reported previously. A novel one-electron two-proton reaction mechanism has been proposed to explain the distribution-enhanced direct eT. The enhanced eT is well displayed on the Hb-in-TNAs based H2O2 sensor, which exhibits a sensitivity of as high as 0.919 m Lambda mM(-1) cm(-2), a detection limit of as low as 7.0 x 10(-8) M at a signal-to-noise of 3, and a wide linear detection range from 10(-8) to 10(-3) M.