Amperometric urea biosensor based on urease and electropolymerized toluidine blue dye as a pH-sensitive redox probe

The electropolymerized toluidine blue film deposited on the glassy carbon electrode show amperometrically detectable pH sensitivity. This feature of polytoluidine blue (PTOB) film was used for a construction of an amperometric urea biosensor. We have observed a linear shift of the formal redox potential with increasing pH value between 4 and 8 giving the slope of 81 mVΔ pH−1. Polytoluidine blue film has had a significantly increased stability and higher electrochemical activity compared to the adsorbed monomeric dye. The polytoluidine blue urea biosensor has been operating at a working potential of −200 mV vs. SCE. The sensitivity of the biosensor was 980 nA mM−1 cm−2. The biosensor showed linearity in concentration range up to 0.8 mM with the detection limit of 0.02 mM (S/N=3).