Porous nanomaterials provide a larger surface area available for enzyme binding and decrease the diffusion distance for the substrate to access the immobilized enzyme,which may improve the performance of the enzyme
electrode. Besides,the close enzyme–substrate contact through covalent bonding,may promote faster detection kinetics,once the electrochemically detectable species(ammonia) is produced closer to the transducer,reducing diffusion resistance,and thus increasing sensitivity and diminishing response times. Impedimetric analysis of the proposed biosensor indicated a fast response time of less than 4 s with a wide linear range from 0.83 to 23.24 mM and limit of detection as 0.40 mM for urea.