Electrochemiluminescent pH sensor measured by the emission potential of TiO2 nanocrystals and its biosensing application

This work reports for the first time a potential-based nano-electrochemiluminescent (ECL) pH sensor, using anatase TiO 2 nanocrystals (NCs) as the ECL probe. The first ECL peak potential of the TiO 2 NCs shifted negatively with increasing pH, showing a linear range from −0.47 V (vs Ag/AgCl) at pH 3 to −1.06 V at pH 10. This phenomenon was attributed to the absorption of ‘potential-determining ions’ of OH − on the surface of TiO 2 NCs, leading to larger impedance of the electron injection. Other common ‘potential-determining ions’, such as phosphate, induced a slight potential shift of 0.03 V at a concentration of 0.1 M. Using urease as an enzyme model, a urea biosensor was developed by the simultaneous modification of urease and TiO 2 NCs on indium–tin oxide (ITO) electrodes. The biosensor, measured on the basis of the pH increase caused by the enzyme catalysis reaction, had a linear range of 0.01–2.0 mM, with a potential shift of 0.175 V. The as-prepared pH sensor, which has simple construction procedures and acceptable sensitivity and selectivity, may provide new avenues for the construction of ECL bioanalytical methodologies. Copyright © 2014 John Wiley & Sons, Ltd.