Chemical/biochemical sensor/monitors

This volume presents a cross section of recent advances in the development of novel chemical and biochemical sensors for on-line monitoring and control applications in the environmental, clinical, and bioprocess areas. These chapters illustrate how many of the key challenges for continuous monitoring are being addressed. The methods discussed include optical techniques ranging from near-infrared spectroscopy to lifetime-based phase fluorometry biosensors ranging from optical immu-nosensors to enzyme-electrodes as well as electrochemical, acoustic, and plasmon resonance techniques. 

In the following, only chemical and biochemical sensors are considered They make use of specific "key-lock" interactions which convert chemical to electronic information Three different tasks are usually fulfilled by chemical sensors, i e the quantitative and selective determination of individual particles (such as molecules or ions in gases or liquids), the determination of gross parameters (such as toxicity), or the quantitative characterization of odors (such as smells monitored qualitatively by the human nose) These requirements can only be achieved with sensor systems which in the most general case contain ten components for analyzing gases or liquids [4]... 

CO and hydrocarbon content). Such instruments are already in use in other fields. Chemical and biochemical sensors may eventually lead to specific monitoring of more complex molecules. There are already such devices for war gases and for most of the drugs of abuse. 

Microelectronic circuits for communications. Controlled permeability films for drug delivery systems. Protein-specific sensors for the monitoring of biochemical processes. Catalysts for the production of fuels and chemicals. Optical coatings for window glass. Electrodes for batteries and fuel cells. Corrosion-resistant coatings for the protection of metals and ceramics. Surface active agents, or surfactants, for use in tertiary oil recovery and the production of polymers, paper, textiles, agricultural chemicals, and cement. 

Optical sensors (Figure 1) can be defined as devices for optical monitoring of physical parameters (pressure1, temperature2, etc.) or (bio)chemical properties of a medium by means of optical elements (planar optical waveguides or optical fibres). Chemical or biochemical fibre-optic sensors3 are small devices capable of continuously and reversibly recording the concentration of a (bio)chemical species constructed be means of optical fibres. 

Although we currently master the principles underlying spontaneous emission of light from electronic excited states, fluorescence will continue by helping chemical and biochemical sensing due to its many advantages and applications. Among them fluorescent sensors will certainly monitor our environment, our industrial processes and our health. 

Recent developments in microsystems technology have led to the widespread application of microfabrication techniques for the production of sensor platforms. These techniques have had a major impact on the development of so-called Lab-on-a-Chip devices. The major application areas for theses devices are biomedical diagnostics, industrial process monitoring, environmental monitoring, drug discovery, and defence. In the context of biomedical diagnostic applications, for example, such devices are intended to provide quantitative chemical or biochemical information on samples such as blood, sweat and saliva while using minimal sample volume. 

A survey of the optical bandgap, excitonic recombination properties under low excitation and electron hole plasma recombination in AlxGai.xN has been given. Demand for UV applications, i.e. gas sensors or monitors, flare sensors, medical applications, chemical and biochemical applications and light sources for phosphors increases rapidly, which will surely lead to the further improvement of the quality of the AIN containing nitrides, and thus give us much more information about their luminescence properties. 

Biosensors can be defined as chemical sensor systems in which an analyte is detected based on biochemical processes or biochemical utilization. A biosensor is mostly composed of a biological element responsible for sampling and tracing, and a physical element called a transducer responsible for sample transmission and further processing (see also Part V, Chapters 8 and 9). The term biosensor does not really meet the lUPAC definition, in which sensors are defined to be self-containing, perform continuous monitoring and are reversible. For the purpose of this chapter, the term biosensor will not be so strictly used as in the traditional context. 

This article will concern itself only with devices that involve a chemical or biochemical transduction mechanism to generate the analytical information, with the processes occurring in a membrane or layer attached to the probe in such a manner that the analytical information can be accessed electronically from the outside world. This covers sensors that are for single use and for continuous monitoring because the basic chemistry and sensor configuration used are very similar for a particular application. Hence, the article does not cover techniques such as open-cell Fourier transform infrared or remote fiber spectroscopy, which can be used to sense the chemical nature of the environment without involving the use of a bona fide sensor. 

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