Screen Printed Potentiometric Sensor for Non-Invasive Measurement of Blood Urea in Human Subjects Using Reverse Iontophoresis

A screen printed potentiometric urea biosensor is developed to monitor blood urea level non-invasively using reverse iontophoresis. The extraction and sensing system consists of a reverse iontophoresis electrode, a working electrode and a reference electrode. The working electrode is screen printed using graphitic carbon paste, reference and reverse iontophoresis electrodes are screen printed using silver/silver chloride (Ag/AgCl) paste. Urease enzyme is immobilized in the polypyrrole matrix on the working electrode using cyclic voltammetry, having potential window of -0.1 v to 0.8 v and scan rate of 50 mV/s for 5 deposition cycles. Scan rate and deposition cycles are optimized for cyclic voltammetry to immobilize the urease enzyme in polypyrrole matrix to obtain maximum sensor performance. The stability of screen printed reference electrode (SPRE) is probed with standard calomel electrode and found to be stable for more than 60 minutes. The enzyme leaching test on working electrode is conducted using indophenol method and confirms that there is no leaching of enzyme from the electrodes. Scanning Electron Micrograph (SEM) of deposited polyrrole shows that microstructured film is deposited on the working electrode. X-ray diffraction (XRD) and Raman spectroscopy are performed to analyze composition of deposited film and they confirm the presence of all mandatory functional groups of polypyrrole in the deposited film. Electrochemical active area is calculated through cyclic voltammetry and there is 55- 60% increase in electrochemical active area compared to bare graphitic carbon electrode due to the formation of polypyrrole microstructure on the working electrode. The developed screen printed sensors exhibited sensitivity of 35.07 mv/decade and showed liner response for the range, 10 μM to 5 mM with correlation co-efficient of 0.995. Interference studies with KCl, NaCl and MgCl solutions are performed and found that there are no significant changes in the sensor performance. These tests affirmed that the developed sensors are useful for conducting in-vivo studies to measure blood urea level non-invasively through reverse iontophoresis. Developed urea sensor is validated by conducting clinical investigations on 10 human subjects. The correlation co-efficient is arrived between blood urea level and transdermal extracted urea level and it is found to be 0.391.