Amperometric Enzyme-based Biosensors for Lowering the Interferences

Abstract

1.1 Glucose, enzymes and mediators Glucose becomes more and more important and popular research topics for medicine and biochemistry that monitoring biomarkers of chronic diseases, such as glucose to diabetes, bilirubin to jaundice and creatinine to kidney disease. Among many biomarkers, glucose is a common and an important biological species of human blood, found out normally in the range of about 4~8 mM. According to statistical information system of World Health Organization (WHO), the number of people with diabetes is estimated more than 180 million worldwide and it is likely to more than double by 2030. Besides, it is also estimated that 9% of all deaths worldwide are due to diabetes. Most notably, diabetes deaths are projected to increase by over 80% in upper-middle income countries between 2006 and 2015. Therefore, it is necessary to develop an efficient glucose biosensor for monitoring the glucose level of diabetics. Glucose is an attractive target, because it is not only an important biomarker for diabetes but also a kind of fuel for biofuel cells. In other words, the glucose biosensor can work for detecting the glucose level and for the anode of the biofuel cell. The biofuel cells were intended to power cardiac assist devices, such as artificial hearts or cardiac pacemakers (Rao & Richter, 1974; Rao et al., 1974). For getting a good specific property, enzymes are widely applied as recognized molecules. Two kinds of enzymes with different redox potentials and electron transfer pathways are usually used to catalyze the glucose. One is the glucose oxidase (GOD) (Franke & Deffner, 1939) from Aspergillus niger and the other is glucose dehydrogenases (GDH) from Acinetobacter calcoaceticus. For GOD catalyst, the cofactor is flavin adenine dinucleotide (FAD) with a strong bond to apo-GOD, but the cofactor can be nicotinamide adenine dinucleotide (NAD) (Boguslavsky et al., 1995), FAD (Tsujimura et al., 2006) and pyrrole quinoline quinone (PQQ) (Duine et al., 1979) for GDH. As an example, the FAD-GOD was selected in this chapter as the recognized molecule. The FAD-GOD has an apparent formal redox potential of -0.048 V vs. standard hydrogen electrode (SHE) (Kulys et al., 2006) and it has a catalyzed rate of 5×103 glucose molecules per second (Willner et al., 2007a). The series catalytic mechanisms in a solution with oxygen are shown in Eqs. (1) and (2) (Warburg & Christian, 1932).