Electrochemical-based sensor devices

Multisensor chemical arrays and aptasensors are generally electrochemical-based sensor devices (eg, potentiometry, amperometry, voltammetry, and impedance spectroscopy). 

Amperometric biosensors are generally composed of conventional metal electrodes and mediators that can shuttle electrons from the electrode to the active centre commonly buried deep within the polypeptide structure of the enzyme. Synthetic metals, including poly aniline, have also attracted considerable attention as electrochemical transducers for a variety of enzyme-based sensor devices. Significantly, these electrodes facilitate electron transfer to an enzyme without an added mediator species. This approach has simplified the construction of biosensors and also obviates sluggish kinetics, which are deleterious to precise detection (Figure 12.27)... 

Sensors and Measurement Devices There are many sensors based on electrochemical reactions. A common example is the thermocouple, which exploits the thermodynamically governed relationship between temperature and voltage between the junction of two dissimilar metals. Other electrochemical-based sensors for physical parameters, species detection, or other uses are common. 

Enzyme sensors can measure analytes that are the substrates of enzymatic reactions. Thermometric sensors can measure the heat produced by the enzyme reaction [31], while optical or electrochemical transducers measure a product produced or cofactor consumed in the reaction. For example, several urea sensors are based on the hydrolysis of urea by urease producing ammonia, which can be detected by an ammonium ion-selective ISE or ISFET [48] or a conductometric device [49]. Amperometric enzyme sensors are based on the measurement of an electroactive product or cofactor [50] an example is the glucose oxidase-based sensor for glucose, the most commercially successful biosensor. Enzymes are incorporated in amperometric sensors in functionalised monolayers [51], entrapped in polymers [52], carbon pastes [53] or zeolites [54]. Other catalytic biological systems such as micro-organisms, abzymes, organelles and tissue slices have also been combined with electrochemical transducers. 

The most important direction for future research is the application of the multiscale systems approach to a broad range of additional non-trivial systems. There are a large number of such candidates, including many in which electrochemical phenomena play a significant role. The greatest number of electrochemical-based applications in the near term is likely to be in micro- and nanoelectronics, given the head-start in applications of multiscale simulation and the intense interest of the semiconductor industry, as cited earlier in this chapter. Additional applications are likely to arise in nanobiomedical sensors and other nanobiological devices, many of which are closely related to micro- and nanoelectronic processes in terms of chemistry, physics, materials and components. The pursuit of specific applications will also serve to improve the systems tools, as any nontrivial applications are apt to do. 

The electrochemical single or double stranded DNA sensors are usually proposed as screening devices for monitoring samples that may contain toxic compounds but not endorsed as toxicity tests. If the samples are positive then better care should be taken to handle and analyze these samples using other toxicity tests. DNA-based sensors have seen great expansion in their use as tools for detecting toxic compounds,... 

Integration of a dialysis membrane or coupling to a microdialysis probe can help to exclude many of the larger molecules such as proteins that are typically responsible for fouling the sensor elements of microchip analysis systems. The nature of the analysis will dictate whether coupling to a flowthrough or separation-based sensor must be achieved and the kind of detection elements to be employed (optical, electrochemical, etc.). One of the issues with microchip devices is the very small... 

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