Enzymatic biosensors are intensively investigated and developing group of chemical sensors. Construction of simple, low cost and disposable sensors is one of main directions of recent studies. Conducting polymers are promising materials for application in construction of biosensors and can be a matrix for immobilizing enzymes or mediator transferring the signal from the analyte. The signal can result from changes of the polymer properties. The applied conducting polymer was commercially available polyaniline dispersion which was simply cast on a transparent plastic support. Then, a cellulose acetate membrane containing an enzyme was deposited on the polyaniline layer. As a model system urea sensor with urease was chosen. Urease catalyzes the hydrolysis of urea into carbon dioxide and ammonia:

CO(NH₂)₂ + 2 H₂O + H⁺ -> 2 NH₄⁺ + HCO₃^-

Ammonia leads to local pH increase and consequently to deprotonation of polyaniline. Polyaniline deprotonation results in open circuit potential decrease of the polymer layer, conductivity decrease as well as VIS-spectrum changes dependent on pH change. Either can be easily monitored, and their application for urea sensing purposes is demonstrated. Parameters of determination were optimized and an example of calibration plot was shown on Fig. 1.

Fig. 1. Analytical characteristic of urea biosensor (absorbance at wavelength 584 nm vs logarithm of urea concentration)

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