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Biosensors for last two decades make ideal sensing systems to monitor the effects of pollu‐ tion on the environment, in the food or textile industry as well as medical diagnostic due to their biological base, ability to operate in complex matrices, short response time and small size.

In enzymatic devices, efforts have been concentrated on the control over enzyme activity, which is highly dependent on the interface between the electrode and the enzyme. Such con‐ trol has led to immobilization techniques suitable for anchoring the enzyme close to elec‐ trode with preservation of its biological activity. In these type of devices, where retaining of the enzyme activity at the electrode/enzyme interface is the key to design efficient electrode, charge transfer between enzyme and electrode should be fast and reversible. Moreover, the charge transfer may also be optimized with some mediating particles (i.e. conducting units) being used in conjunction with the biological molecules at the electrode surface. To the use of conducting polymers for the fabrication of various biosensors have been dedicated exten‐ sively study due to their redox, optical, mechanical and electrical properties, as well as to their unique capability to act both, as transducers, and an immobilization matrices for en‐ zyme retention [1].

It is essential for the sensitivity of the system that the recognition units have optimized sur‐ face density, good accessibility, long-term stability and minimized non-specific interactions with compounds other than the analyte. Such model molecular assemblies can be prepared by Langmuir-Blodgett (LB) and Langmuir-Schaefer (LS) techniques [2,3], layer-by-layer (LbL) or by employing self-assembly monolayers (SAMs) or electrolytic deposition (Fig. 1) [4,5]. The main advantage of using thin films to build a biosensor is the possibility to de‐ crease dramatically the response time of the device. Langmuir-Blodgett type technology al‐ lows building up i.e. lamellar lipid stacking at an air/water interface, which can be easy

© 2013 Cabaj and Sołoducho; licensee InTech. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2013 Cabaj and Sołoducho; licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

transported onto a solid support. When all parameters are optimized, this technique corre‐ sponds to one of the most promising for preparing thin films of amphiphilic molecules. Based on the self-assembled properties of amphiphilic biomolecules at the air/water inter‐ face, LB technology offers the possibility to prepare biomimetic layers suitable for adsorp‐ tive immobilization of bioactive molecules [6].

Proteins are more challenging to prepare for the different microarray than i.e. DNA, and protein functionality is often dependent on the state of proteins. Since enzymes often signifi‐ cantly reduce their activity during immobilization, the optimized adsorption methods seem to be optimal for the retaining of conformational states of proteins on solid surfaces. Among the various immobilization techniques available, adsorption may have a higher commercial potential than other methods because the adsorption process is simpler, less expensive, re‐ tains a high catalytic activity, and most importantly, the support could be repeatedly reused after inactivation of the immobilized enzyme.

Enzyme-based biosensors play an important role in various industries, such as food, manu‐ facturing, clinic, and environment. Recently, mediators have been employed in enzymebased biosensors in order to shuttle electrons between the redox enzyme and the electrode surface. Solution-phase mediators may cause electrode contamination and operation incon‐ venience. In order to overcome the above-mentioned drawbacks and improve the perform‐ ances of the biosensors, the immobilization of the mediator with protein on a solid support provides a new way to construct reagentless biosensors [7].

However, there is many techniques of biocatalysts immobilization and much research is dedicated to fabricate the biosensing elements, the construction of novel type of biosensor is challenge for new technologies and the key problem is modification of electrode by enzyme using thin film preparation methods.

**Figure 1.** Layered biosensor system
