Biosensors biologically active materials

The basic requirement in biosensor development is ascribed to the successful attachment of the recognition material, a process governed by various interactions between the biological component and the sensor interface. Advanced immobilization technologies capable of depositing biologically active material onto or in close proximity of the transducer surface have been reported. In this context, the choice of a biocompatible electrode material is essential. The material surfaces (support) include almost all material tjrpes metals, ceramics, polymers, composites and carbon materials [8]. In most cases, when a native material does not meet all the requirements for... 

Optical biosensors comprise a rather heterogeneous group of sensors in which the interaction of light with an immobilized biologically active material is sensed. They often contain a light source in addition to the signal transducer. 

A MEMS-based biosensor is a biosensor which is realized by microfabrication technology and takes advantage of the small size. It incorporates a biological component with a physiochemical transducer such as a microsystem. It is a special class of chemical sensor that takes advantage of the high selectivity and sensitivity of biologically active materials. It involves immunoenzyme and microorganism sensors. 

MEMS biosensor based on the unique properties of nanowire enables highly sensitive and selective detection because nanowire as an electrode has a high surface-to-volume ratio for adsorption. When a chemically functionalized nanowire is immersed in an analyte solution, analytes react to biological active materials. As results of the reaction, electrical properties of the nanowire such as resonant frequency, conductivity, and resistance are changed [20, 21]. Schematic and SEM images of a MEMS-based nanowire biosensor are shown in Eig. 9. 

When a biologically active material interacts with an analyte, a physicochemical change takes place that is converted into an electrical output signal using a suitable transducer. Based on various types of transducers, biosensors may be classified into optical, calorimetric, piezoelectric and electrochemical biosensors. Cooper and Hall have reported the electrochemical response of a GOD loaded PANI film [84]. Mu and co-workers have studied the bioelectrochemical response of the PANI-uricase electrode [162]. 

The construction principle of any biosensor type is based on the use of two functionally different components (Figure 8.1) a bioselective membrane (a bioselector representing a biologically active, immobilized material) and a physical converter of the chemical signal (a transducer). The bioselector is applied directly to the transducer surface, which transforms... 

Nowadays, the construction of electrochemical biosensors based on the use of gold nanoparticles constitutes an intensive research area because of the unique advantages that this nanomaterial lends to biosensing devices. So, gold nanoparticles provide a stable surface for immobilization of biomolecules with no loss of their biological activity. Moreover, they facilitate direct electron transfer between redox proteins and electrode materials, and constitute useful interfaces for the electrocatalysis of redox processes of molecules such as H202 or NADH involved in many biochemical reactions (1, 2). 

Neutral molecules can also be incorporated into clay materials by taking advantage of their sorption properties. The mild environment of the interlayer region provides an ideal matrix for biologically active molecules. Thus, biosensors can be constructed by incorporation of enzymes into the film (98). The enzyme can then act as a mediator for the target biomolecule. 

Magnetic biomedical materials are typically composed of a magnetie eore, a biocompatible shell, and one or more biologically active moleeules (drug, antibody, enzyme, etc.) anchored to the surface. As detection agents, they are very useful in diagnosis. In eombination with recently developed magnetie biosensors (10 mole/L), they have opened new fi-ontiers in early detection of diseases, and inmunoassays. " Their use in MRI permits the real time in... 

Similarly to the above-mentioned entrapment of proteins by biomimetic routes, the sol-gel procedure is a useful method for the encapsulation of enzymes and other biological material due to the mild conditions required for the preparation of the silica networks [54,55]. The confinement of the enzyme in the pores of the silica matrix preserves its catalytic activity, since it prevents irreversible structural deformations in the biomolecule. The silica matrix may exert a protective effect against enzyme denaturation even under harsh conditions, as recently reported by Frenkel-Mullerad and Avnir [56] for physically trapped phosphatase enzymes within silica matrices (Figure 1.3). A wide number of organoalkoxy- and alkoxy-silanes have been employed for this purpose, as extensively reviewed by Gill and Ballesteros [57], and the resulting materials have been applied in the construction of optical and electrochemical biosensor devices. Optimization of the sol-gel process is required to prevent denaturation of encapsulated enzymes. Alcohol released during the... 

Biomaterials such as proteins/enzymes or DNA display highly selective catalytic and recognition properties. Au nanoparticles or nanorods show electronic, photonic and catalytic properties. The convergence of both types of materials gives rise to Au NP-biomolecule hybrids that represent a very active research area. The combination of properties leads to the appearance of biosensors due to the optical or electrical transduction of biological phenomena. Moreover, multifunctional Au NP-peptide hybrids can be used for targeting nuclear cells where genetic information is stored and could be useful for biomedical applications [146]. 

While the variety of NPs used in catalytic and sensor applications is extensive, this chapter will primarily focus on metallic and semiconductor NPs. The term functional nanoparticle will refer to a nanoparticle that interacts with a complementary molecule and facilitate an electrochemical process, integrating supramolecular and redox function. The chapter will first concentrate on the role of exo-active surfaces and core-based materials within sensor applications. Exo-active surfaces will be evaluated based upon their types of molecular receptors, ability to incorporate multiple chemical functionalities, selectivity toward distinct analytes, versatility as nanoscale receptors, and ability to modify electrodes via nanocomposite assemblies. Core-based materials will focus on electrochemical labeling and tagging methods for biosensor applications, as well as biological processes that generate an electrochemical response at their core. Finally, this chapter will shift its focus toward the catalytic nature of NPs, discussing electrochemical reactions and enhancement in electron transfer. 

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