Polyelectrolyte-Based Enzymatic Diagnosticum with Precipitation Detection System for Urea Assay in Solution

A polyelectrolyte-based enzymatic diagnosticum with a precipitation detection system that can be used as a biosensor was created. The detection method was based on the change in polyelectrolyte microcapsule weight with respect to the urea content. The possibility of biosensor reutilization was demonstrated. The appropriate ionic precipitator causing precipitation of insoluble carbonate within the microcapsules and the optimal microcapsule titre were found. In the solution of monovalent anions (chlorides), the activity of encapsulated urease was shown to increase monotonically as the square root of the ionic strength depending on the elevation of the salt content. The activity drastically increased in a narrow concentration interval (0.6–0.8 mM) of divalent anions (sulfates) and reached the level of the native enzyme activity.