Biosensor device

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... 

OPTICAL BIOSENSOR DEVICES AS EARLY DETECTORS OF BIOLOGICAL AND CHEMICAL WARFARE AGENTS... 

Biosensor devices must operate in liquids as they measure effects at a liquid-solid interface. Then, the immobilization of the receptor molecule on the sensor surface is a key step for the efficient performance of the sensor. When the complementary analytes are flowing over the surface, they can be directly recognized by the receptor through a change in the physico-chemical properties of the sensor. In this way, the interacting components do not need to be labeled and complex samples can be analyzed without purification. 

J. Sefconicova, J. Kahlik, V. Stefuca, et al, A filtration probe-free on-line monitoring of glycerol during fermentation by a biosensor device. Enzyme Microb. Technol, 42, 434 39 (2009). 

The book covers the entire field of electrochemical (bio)sensor design and characterization and at the same time gives a comprehensive picture of (bio)sensor applications in real clinical, environmental, food and industry-related samples as well as for citizens safety/security. In addition to the chapters, this volume offers 53 step-by-step procedures ready to use in the laboratory. This complementary information is offered on a CD-ROM included with the book in order to facilitate hands-on information on the practical use of electrochemical biosensor devices for the interested reader. It is the first time that the Comprehensive Analytical Chemistry series offers such complementary information with detailed practical procedures. 

Screen-printing is a proven technology, readily adaptable to the manufacture of diverse sensor/biosensor devices for a wide range of applications, and has great potential for new devices, particularly where simplicity of fabrication, and operations at low cost, are important factors. Future devices are likely to incorporate nanoparticles where enhanced sensitivity with miniaturisation may be required. 

Redox enzymes are the active component in many electrochemical enzyme electrode biosensor devices.1821 The integration of two different redox enzymes with an electrode support, in which one of the biocatalysts is photoswitchable between ON and OFF states, can establish a composite multisensor array. The biomaterial interface that includes the photoswitchable enzyme in the OFF state electrochemi-cally transduces the sensing event of the substrate corresponding to the nonphoto-switchable enzyme. Photochemical activation of the light-active enzyme leads to the full electrochemical response, corresponding to the analysis of the substrates of the two enzymes. As a result, the processing of the signals transduced by the composite biomaterial interface in the presence of the two substrates permits the assay of the... 

For biosensor devices these problems are aggravated because of the additional integration of a biological component on a planar device surface [50]. 

Hybride micro-FIA systems produced in silicon technology using oxygen microelectrodes and microcavities have been developed for measuring phosphate concentrations [96]. Multiple analyte biosensor arrays can also be realized using thin film and silicon technology. The so-called containment technology has been applied to immobilize enzymes in three dimensional cavities formed in silicon wafers to get fully process compatible biosensor devices [97] (Fig. 5). 

The hydrophobias are a case where protein nanofibers can play a dual role in creating a biosensor. They can aid in the immobilization of bioactive components within a biosensor and also add further functionality to the transducing element of a biosensor device. Hydrophobins are self-assembling [3-sheet structures observed on the hyphae of filamentous fungi. They are surface active and aid the adhesion of hyphae to hydrophobic surfaces (Corvis et al., 2005). These properties can be used to create hydrophobia layers on glass electrodes. These layers can then facilitate the adsorption of two model enzymes glucose oxidase (GOX) and hydrogen peroxidase (HRP) to the electrode surface. The hydrophobin layer also enhances the electrochemical properties of the electrodes. 

Cellular biosensors have been widely described [11-55]. In many cases, the cells have been used in a manner analogous to that of enzyme based devices simply because they contain substantial quantities of particular enzymes. There are, of course, advantages to this approach since the enzymes do not have to be isolated and so may be cheaper but also more active and more stable than the purified components. However, the reproducibility, speed of response and selectivity of the cell based devices will, in general, be less favorable than their enzyme based counterparts. This is because of the relatively large physical size of the cells, the presence of membranes that hinder diffusion and the presence of enzymes other than the one(s) of particular interest. Nevertheless, a range of approaches has been adopted to improve the selectivity and other characteristics of whole cell biosensor devices. These were reviewed by Racek [11] and include ... 

An alternative approach, adopted by Albery et al. [59-61], is to determine the mechanism giving rise to the sensor response and to use this information together with the measured data at short times to calculate the final response. This was used for an electrochemical sensor system incorporating cytochrome oxidase where the steady-state responses of the measurement system were insufficiently fast for useful measurement of respiratory inhibitors such as cyanide, hydrogen sulphide, etc. By using mechanistic information, it was possible to successfully calculate the concentration in a test sample by real-time analysis of the sensor signals at short times after exposure to the test sample. The analysis could cope with the gradual loss of enzyme activity commonly found in these biosensor devices. 

Fig. 5.8. (a) MZI configuration (b) Structure of a MZI biosensor device based on TIE waveguides. Note the dimensions of the rib channel (4 nm) for monomode and high sensitivity waveguides. 

Recently, a commercial biosensor device based on interferometry (Ana-light Bio200) produced using planar waveguides was introduced by the company Farfield sensors [61],... 

M.M. Rhemrev-Boom, J. Korf, K. Venema, G. Urban and P. Vadgama, AversatUe biosensor device for continuous biomedical monitoring. Biosens. Bioelectron., 16... 

Functionalization of surfaces with photopolymerized monomers or sol-gel matrices has also been used. In this case, the biomolecules can be physically entrapped within the supporting matrix. The method is applicable for almost all types of surfaces, it is easy to handle, and the large spectrum of monomer precursors commercially available permits the immobilization of basically all biological elements. In this case, the absence of chemical bond formation helps to preserve the activity of the bioreagent during the immobilization process. However, several drawbacks such as leaking of biocomponent and possible diffusion barriers restrict the performance of biosensor devices fabricated using this procedure. 

A gold quartz crystal surface can be easily functionalized with an avidin monolayer (Fig. 7.3) that will then allow immobilization of any biotinylated biomolecule through strong avidin-biotin interaction. The only requirement for the development of a successful biosensor device is the availability of biotin-tagged molecules. We have used this strategy to achieve DNA electrode materials without the need for hybridization [44-46]. The dsDNA serial assembly was achieved by first linearizing circular plasmid... 

In order to develop a reliable biosensor device, a straightforward engineering materials approach must be considered. Commonly used coating materials include polymers, metals and alloys, ceramics, inorganic semiconductors,... 

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