Urea sensing characteristics of titanate nanotubes deposited by electrophoretic deposition method

Urea sensing properties of titanate nanotubes (TNT) are presented here. TNT films were deposited by electrophoretic deposition (EPD) method on aluminum substrate. Prior to EPD, commercial nanoparticles of TiO2 were hydrothermally treated at 70 degrees C for 48 h after sonicating the solution for 8 h. Hydrothermal method resulted in the conversion of particles to tubular structure following the established method. Urease was covalently attached with TNT (by soaking in urease solution for 3 h). In general, conductivity of film increases after urease immobilization. The urease immobilized films were characterized for urea sensing in the concentration range of 1 mM to 500 mM. Three different sensitivity regions are observed viz. (i) lower concentrations (below 10 mM); (ii) linear region up to 100 mM and a (iii) saturation region above 100 mM. Sensors are extremely sensitive in region (i). From the elemental analyses of the films after urease immobilization, urease was found attached with TiO2, as evident by N 1s peak in the photoelectron spectra. Cyclic voltammetric studies indicated surface-confined redox couple is responsible for sensing behavior. A possible sensing mechanism is presented and discussed.