Biochemical sensors, miniaturization

Finally, SECM offers a new application area for miniaturized electrochemical and biochemical sensors. They can be used in connection with a positioning system to solve, for instance, problems of cell biology, material science, and interfacial geochemistry. Since SECM instruments are now available from different commercial sources, a much broader application in the electrochemical sensor community is expected within the next years. 

For a general definition of sensors, see - Chemical and Biochemical Sensors. The term sensor denotes a small specialized device that operates selectively on several analytes [167], Optical sensors are certainly competitive with ion-selective electrodes becau.se they are now less complex than in the past and miniaturization promises further success in the future. Furthermore, optical sensors have advantages [168] in remote sensing and by utilization of the spectral information, especially in the case of sensor arrays. 

Progress in semiconductor technology during recent years has made it possible to miniaturize the classical oxygen sensor [74] - [77] for use as a transducer in several chemical and biochemical sensors. 

Stimulated by the current trend of micro-TAS and LOC technologies, biochemical sensor strategies have currently been incorporated in microfluidic systems for the realization of highly sophisticated systems. However, the miniaturization of microfluidic devices depends on micromachining technology and the integration of different components such as pumps and valves on a chip tends to be complicated. 

Modular components of future chemical sensor systems are introduced briefly Their development involves, in particular, new or fine-tuned (well-known) sensor-active materials and transducers A molecular understanding of the sensing mechanisms is shown to be a prerequisite for the development of a new generation of sensor systems with particular emphasis on their miniaturization and integration This understanding requires comparative microscopic, spectroscopic and sensor test studies on prototype materials to be performed, which requires to use experimental setups that combine the usual techniques of interface analysis with sensor preparation and sensor test chambers A few selected case studies on prototype materials are chosen to illustrate recent trends in the development of new materials and transducers for integrated chemical and biochemical sensor systems... 

Significant advances have occurred during the past decade to miniaturize the size of the measurement system in order to make online analysis economically feasible and to reduce the time delays that often are present in analyzers. Recently, chemical sensors have been placed on microchips, even those requiring multiple physical, chemical, and biochemical steps (such as electrophoresis) in the analysis. This device has been called lab-on-a-chip. The measurements of chemical composition can be direct or indirect, the latter case referring to applications where some property of the process stream is measured (such as refractive index) and then related to composition of a particular component. 

Micro flow control devices open new possibilities for the miniaturization of conventional chemical and biochemical analysis systems. The micro total analysis system (pTAS) including microfabricated detectors (e.g. silicon based chemical sensors, optical sensors), micro flow control devices and control/detec-tion circuits is a practical micro electro mechanical system (MEMS). pTAS realize very small necessary sample volume, fast response and the reduction of reagents which is very useful in chemical and medical analysis. Two approaches of monolithic and hybrid integration of these devices have been studied. Monolithic and hybrid types of flow injection analysis (FIA) systems were already demonstrated [4, 5]. The combination of the partly integrated components and discrete components is useful in many cases [6]. To fabricate such systems, bonding and assembling methods play very important roles [7]. 

We are confident that research on optical sensors for chemicals and biochemicals will lead to label-free, multianalyte, highly reliable, highly sensitive, miniature, and expensive sensors. Waveguide sensors will be among the commonly used ones. We shall be delighted if this two-volume work facilitates the emergence of optical sensors with highly desirable attributes. 

A considerable body of research work is directed at the miniaturization of biosensors and the creation of multifunctional sensors by the use of small-scale electronic devices. Semiconductor biosensors have been developed by the biochemical modification of gas-sensitive or ion-sensi-... 

All analysts are familiar with the principles of potentiometry and potarography and indeed, most analytical laboratories will contain a pH meter and a polarograph. However, electrochemical methods arc, in general, not very important in modern analysis. In contrast, there arc spccifiG applications such as trace metal ion analysis in water and effluents and also some other aspects of environmental analysis for which electrochemical methods are particularly attractive. This is because (1) some methods, especially anodic stripping voltammetry, have a very high sensitivity for heavy-metal ions and the lowest detection limit of from 10 to mol dm is well below that of other available methods (2) electrochemical methods are well suited for modification to on-line and/or portable devices for analysis in the held. Whether the analysis is based on current, conductivity or the response of an ion-selective electrode, both the cell and the control electronics are readily miniaturized and operate on low power Hence, this chapter considers the principles of the electroanalytical methods important in environmental and on-line analysis, together with biochemical applications of electrochemical sensors. 

Sensors are small or miniaturized devices designed for the continuous monitoring of the physicochemical or biochemical properties of specific analytes so as to provide qualitative and/or quantitative analytical data. They comprise a thin layer of a chemically or biochemically sensitive substance (matrix and recognition element) in contact with a transducer (i.e. a means of converting the chemical or biochemical information into an electrical or optical signal) (Fig. 1). The transducer signal is then processed by suitable electronic circuitry incorporated into the device. 

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