Urea Biosensor based on Conducting Polymer Transducers

Urea is one of the final products of protein metabolism. In clinical analysis and dairy industry urea is a very significant parameter as excess in blood serum from its permissible range causes dysfunction of the kidney. Hence, its analysis is significant and is carried out frequently in various laboratories [1, 2]. Urea is an omnipresent compound present in blood and various organic fluids. It passes directly into milk through diffusion. Therefore, milk is the second major biological sample for the study of urea concentration [3]. A periodic monitoring of urea in milk can be used to predict the state of animal’s health and predict the protein requirement in its diet [4]. Besides milk, presence of urea in agricultural land as a pollutant due to excessive use fertilizers is also widely known. Various methods used for the determination of urea (without use of biocatalyst) are gas chromatography, calorimetric and flourimetric analysis etc [5]. However, these methods need sample pretreatment which stands as a major disadvantage in their versatility of applications. Alongside, these methods can not used for field monitoring. Therefore, devices developed based on biocatalyst “urease” to analyze urea also known as urea biosensors are of vital importance. The first urea biosensor was developed by Guilbault et al. [6] followed by many clinical and biochemical analysts. For the fabrication of the urea biosensor, urease is immobilized over a substrate. The immobilized urease there after catalyzes the urea conversion in to ammonium and bicarbonate ions based on enzyme substrate reaction. Many biosensors have been developed for the determination of urea in the biological samples namely spectrometry [79], potentiometry with application of pH sensitive electrode or an ion selective electrode or an ion sensitive field effective transistor [10-13], conductometry [14-16], coulometry [17], amperometry [18] and inductometry [19]. Amongst these methods, detection through electrochemical mode is highly adopted and versatile. This method involves the use of electrochemical urea biosensor. In the development of electrochemical urea biosensors, immobilization of urease over electrodes is the key parameter which decides the sensitivity and reproducibility of the sensor. Urea biosensors are collectively formed by biorecognition layer biocatalyst i.e. urease, a biotransducer – to read change in physical environment and convert into electronic signal. The complete working principle of the biotransducer component of urea biosensor is shown in Scheme 1. For making biotransducer and choice of substrate, conducting polymers are Source: Biosensors, Book edited by: Pier Andrea Serra, ISBN 978-953-7619-99-2, pp. 302, February 2010, INTECH, Croatia, downloaded from SCIYO.COM