Other biosensors

Substances that are neither enzymes, microorganisms nor immunoagents can also be used in conjunction with transducers to construct biosensors. These include sections of animal and plant tissue, neuroreceptors and chemoreceptors. 

---

Several other biosensors have been developed usiag this oxygen-quenched fluorescence approach. Target species iaclude ethanol [64-17-5] hydrogen peroxide [7722-84-17, H2O2, lactate, and xanthine [69-89-6] C H4N402, usiag alcohol oxidase, catalase [9001-05-2] lactate oxidase, and xanthine oxidase, respectively. An additional technique for biocatalytic biosensors iavolves the firefly chemiluminescent reaction (17) ... 

Composite potentiometric sensors involve systems based on ion-selective electrodes separated from the test solution by another membrane that either selectively separates a certain component of the analyte or modifies this component by a suitable reaction. This group includes gas probes, enzyme electrodes and other biosensors. Gas probes are discussed in this section and chapter 8 is devoted to potentiometric biosensors. 

Other oxidoreductases (dehydrogenases) use electron acceptors other than oxygen, such as the cofactor NAD or NAD(P)". These cofactors maybe advan-t eously combined with electrochemical sensors, provided that the cofactor is externally supplied or immobilized and regenerated. More than 250 highly specific dehydrogenases are commercially available. Hydrolases are another class of readily available enzymes that can be combined with potentiometric sensors. Hydrolases catalyse the hydrolytic cleavage of C-O, C-N, C-C, and other bonds. Other biosensors can be fabricated from the new generation of hybrid and synthetic enzymes (17). 

As was indicated in Section 3.3, an issue to be addressed before glucose or other biosensors is a commercially practical sensor fabrication. An easier and simpler sensor fabrication method was recently investigated using ferrocene modified redox polymer hydrogels. Sirkar and Pishko reported amperometric biosensors based on oxidoreductase immobilization in UV-photopolymerized... 

The use of enzyme labels in ELIS A-type immunosensors and simple amperometric detection schemes resulted in simple and cost-effective alternatives to fluorescence immunosensors. In particular, the use of alkaline phosphatase as enzyme label allowed for the fabrication of advanced immunosensors with signal amphfi-cation by means of redox cycling, which has been a success story of its own. This detection scheme has been used in immunosensors and other biosensors and has stimulated significant developments in electrode fabrication. Instrumental electroanalysis, namely capacitance measurements and EIS allow for label-free detection of immunoreactions. 

In this chapter, we focus on the use of the continuous resonance QCM and EQCM devices to study enzymatic polymerization reactions, biochemical and biomimetic processes and to create thin polymer films electrochemically on the QCM electrode surface. We describe some QCM applications of thin polymer films in enzyme electrode and other biosensors and briefly describe specific cell binding systems to create whole cell biosensors. 

Other biosensor-based diagnostic instruments, such as the enzyme-electrode-based analyzers of YSI for glucose and lactate, are utilized routinely in many clinical laboratories. i-Stat recently introduced a portable analyzer for bedside use which utilizes enzyme-electrode-based assays for glucose and urea, as well as chemical sensor tests for nitrogen, sodium, potassium, and chloride. 

Brandt and J. D. Hoheisel, Peptide nucleic acids on microarrays and other biosensors. Trends Biotechnol. 22, 617-622 [2004). 

Enzyme sensors for carbohydrates. An enzyme electrode for glucose was the first electrochemical biosensor studied [1] and since then intensive research has taken place, providing new ideas and experiences for the development of other biosensors. Glucose biosensors usually use as a biological component the relatively stable enzyme glucose oxidase, preferably from Aspergillus niger (Fig. 14). This enzyme may serve as a model for all flavin oxidoreductases which can be applied not only for... 

Other biosensors and analyzers are constructed on a similar principle, but often using cells rather than enzymes (see section 4.3.2). 

This is an example of a biosensor that uses current as an output. Other biosensor systems have been developed that use similar methods for the detection of cholesterol, glucose and hydrogen peroxidise [41,42]. 

To get an insight into the technical details involved in wearable tattoos, patches, and other biosensors, in the remainder of this chapter we will first briefly address the mechartisms underlying various detection methods. Following that will be a discussion about the fabrication methods available so far, from the most basic to the highly integrated. The applications of this subclass of WBSs in general health, disease control, and sports are presented. We will end with concluding remarks and future perspectives. 

Various physical transducers can be used to detect interaction of the immobilized DNA probe with the analyte. Commonly used detection systems include optical (MarvUc, 1997 Jordan, 1997 Lee, 2001), electrochemical (Wang, 2001 Palecek, 2001) or mass sensitive devices (Storri, 1998 Ebara, 2000). Considering the growing number of potential applications, simphcity and low cost are some of the major design parameters in both microarray and other biosensor apphcations. Therefore, increased attention has been given to relatively simple detection or sensing techniques such as fluorescence measurements. This method offers faster assays without the need for specific substrate properties such as in the mass-sensitive quartz-crystal microbalance (Storri, 1998 Ebara, 2000) or in more complex optical techniques such as surface plasmon resonance (Jordan, 1997 Lee, 2001). 

We selected the streptavidin-biotin binding interaction for proof-of-concept studies of the immobilized nanoSPR sensor for the following reasons first, because of its very high association constant, streptavidin-biotin binding is insensitive to washing steps, which simplifies the experimental setup. Second, the wide use of this model system for validation of other biosensors enables comparison of the nanoSPR biosensor with other platforms under development. ... 

Several other biosensors for pesticide and toxic metal monitoring are also based on the inhibition of enzymes such as urease for heavy metals, tyrosinase for benzoic acid, thiourea and 2-mercaptoethanol, alcohol dehydrogenase for cyanides and heavy metal salts, amino oxidase for plant growth regulators, aldehyde dehydrogenase for fungicides, cytochrome c for cyanides, catalase for heavy metals, and peroxidase for cyanides and heavy metals. Thus, biosensors based on the inhibition of enzymes, suffer from false-positive results. Despite lack of selectivity, this type of biosensor is powerful when rapid toxicity screening is required. 

---