AC impedance measurement for the enzyme kinetics of urea–urease system: a model for impedimetric biosensor

Abstract

The measurement of time evolution of electrochemical impedance enables enzymatic kinetic studies in real-time, and obviates the need of using additional reagents as in many popular spectroscopic methods. This can eventually lead to the development of enzyme biosensors. We have used the urea–urease system as a model for this study. The usage of a free enzyme (without any immobilization steps) in this work makes the technique very simple and unique for electrochemical measurement on urease. The impedance vs. time measurement of urease exhibits Michaelis–Menten (MM) behaviour with the MM constant ($K_{\mathrm {{m}}}$) of 0.8 mM and maximum velocity ($V_{\mathrm {{max}}}$) of $5000\hbox { ohms min}^{{{-1}}}$. This $K_{\mathrm {{m}}}$ value closely matched the one, which is obtained from the conventional colorimetric method (values). The enzyme kinetics was performed in a standard three-electrode system and reproduced in a fabricated mini electrochemical cell in an Eppendorf tube, which could pave the way for the development of impedimetric biosensors for a variety of enzyme systems, especially the ones for which spectrometric techniques cannot be readily applied.