Highly Stable Potentiometric (Bio)Sensor for Urea and Urease Activity Determination.

Marcin Urbanowicz,Kamila Sadowska,Anna Sołdatowska,Agnieszka Paziewska-Nowak,Dorota G Pijanowska

doi:10.3390/membranes11110898

Marcin Urbanowicz, Kamila Sadowska + Show 3 more

Open Access

https://doi.org/10.3390/membranes11110898

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Abstract

There is growing interest for bioanalytical tools that might be designed for a specific user, primarily for research purposes. In this perspective, a new, highly stable potentiometric sensor based on glassy carbon/polyazulene/NH4+-selective membrane was developed and utilized for urease activity determination. Urease–urea interaction studies were carried out and the Michaelis–Menten constant was established for this enzymatic reaction. Biofunctionalization of the ammonium ion-selective sensor with urease lead to urea biosensor with remarkably good potential stability (drift coefficient ~0.9 mV/h) and short response time (t95% = 36 s). The prepared biosensor showed the Nernstian response (S = 52.4 ± 0.7 mV/dec) in the urea concentration range from 0.01 to 20 mM, stable for the experimental time of 60 days. In addition, some insights into electrical properties of the ion-to-electron transducing layer resulting from impedance spectroscopy measurements are presented. Based on the RCQ equivalent circuits comparison, it can be drawn that the polyazulene (PAz) layer shows the least capacitive behavior, which might result in good time stability of the sensor in respect to response as well as potential E0. Both the polyazulene-based solid-contact ion selective electrodes and urea biosensors were successfully used in trial studies for determination of ammonium ion and urea in human saliva samples. The accuracy of ammonium ion and urea levels determination by potentiometric method was confirmed by two reference spectrophotometric methods.

Highlights

The study of enzyme activity is one of the most important biochemical analysis, in both medical diagnosis and in treatment
A highly stable potentiometric biosensor based on the glassy carbon (GC)/PAz system was developed for determination of urea and the enzymatic activity of urease
The study of the individual sensor elements allowed for the development of the optimal composition of the ionselective membrane, the biofunctionalization solution, and the selection among Au, Pt, and GC substrates of the glassy carbon as a material for solid-contact electrode and the conductive polymer

Summary

Introduction

The study of enzyme activity is one of the most important biochemical analysis, in both medical diagnosis and in treatment. Enzyme activity assays are routinely performed in research on cell and tissue engineering, as well as in environmental studied. This induces a growing interest for bioanalytical tools that might be designed for a specific user, primarily for research purposes. Most of literature on the urease activity determination proposes spectrophotometric readout of various indicators [1,2,3,4,5]. To the best of our knowledge, electrochemical sensors are rarely used for measurements of urease activity. Potentiometric sensors are commonly used for urea determination in biological and environmental samples [8,9,10]

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