Distribution-enhanced direct electron communication of hemoglobin immobilized in pristine TiO2nanotube arrays

Abstract

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 (ΔE_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 mA mM⁻¹ cm⁻², a detection limit of as low as 7.0 × 10⁻⁸ M at a signal-to-noise of 3, and a wide linear detection range from 10⁻⁸ to 10⁻³ M.