Glucose biosensors

Glucose Sensors based on immobilization of Glucose Oxidase through thin film science.
Priscila Gonzalez Barba The importance of nanotechnology glucose sensors is discussed. The review covers the basic functionality of the amperometric/potentiometer and organic thin-film transistors (OTFTs) biological sensors. The importance of the enzyme immobilization on the matrix layer is emphasized and theroll of thin film science in this area is presented. The deposition methods used for organic and inorganic matrices are briefly explained and the main advantages of specific examples are pointed out. Keywords Biosensors Glucose sensor Glucose oxidase Organic thin film transistor (OTFT) Enzyme immobilization. Introduction Miniaturized biosensors are of great importance in medicine because they offerseveral advantages over conventional devices as selectivity and best response time and accuracy [1]. As a result of their miniaturized size, these sensors are capable of measuring small features with high resolution and consequently a relatively high concentration of the sample can be saved while measuring only a small amount from it [2]. Nanotechnology biosensors can either be fabricated bymicromachining and/or Silicon technology processes as vacuum evaporation, plasma etching, photolithography, and lift-off. This characteristic promotes the design to be mass production compatible and low cost [3]. The biosensor performance is determined by the coupling between the biological component to be the sensor per se (enzymes) and the solid surface of the transducer (matrix). This is a crucialparameter because the enzymes involve wet processes and the transducers on the other hand involve dry processes hence their compatibility can be limited [4]. The combination technique used to effectively immobilize the enzyme on a surface is called “interfacial design” and it is a matter of thin film science. Thin film technology has been developed to improve and maintain performance, responsetime, accuracy, resolution, stability, reproducibility, and even reusability [5]. Therefore, enzyme immobilization techniques development is essential to improve the capability of biosensors. Different matrices have been studied to avoid denaturation of these enzymes due to harsh treatments required to immobilize them on an electrode surface [6]. Glucose Oxidase (GOx) Enzyme as recognition elementOne of the most clinically essential and thus investigated biosensors is the glucose sensor. Not only is it required for diabetes mellitus monitoring but also for the determination of glucose in food quality control, biochemical research and environmental monitoring [7][8]. Glucose oxidase (GOx) is the most commonly used enzyme for glucose recognition relying on its oxidation [9]. The quantity ofoxidized

analytes can then be electrochemically transformed into a detectable signal. This type of transduction has been studied for several years [10][11] and is importantly popular in the recent years because it has been proved to provide advantages over sensitivity, selectivity, time response and also low cost [12]. Essentially, the GOx enzyme and glucose reaction produces hydrogen peroxide(H2O2) and Gluconolacton (gluconic acid) as described in the following equations: Glucose + GOx ox → Gluconolacton + GOx(red) GOx red + O2 → GOx ox + H2 O2

Amperometric Sensor These sensors can detect the analytes quantitatively through the redox reactions described before. The transducer matrix will produce a current signal proportional to the quantity of glucose participating in theelectrochemical reaction. The GOx will in this case be the electroactive biosensor coupled with the electrode either directly or through an electron transfer mediator [16]. The mediators are the medium through which the electron transfer will occur between the GOx and the electrodes. Some commonly used mediators in oxidaze biosensors are ferrocene, osmium complex, tetrahiafulvalene, and hydroquione. The...