Miniaturized sensors

A significant characteristic of the ISE is the feasibility of fabricating miniature sensors for measurements in samples of very small volume or in vivo Microelectrodes... 

Similar to the case of H-atoms the results obtained fully confirm the validity of expression v = 9Iz, where 9 is the degree of ionization depending on adsorbate, adsorbent, and the temperature. This means that ZnO films (it is also correct both for a CdO layer, and for other chemically stable semiconductor oxides) may be used as very sensitive miniature sensors to determine intensity of atom flow for detected noble metals Ag and Pd (see Table 3.2). If the sensitivity of the measuring equipment is brought up to one can measure atom flows equal to... 

These miniaturized sensors are suitable for flow-injection analysis [130]. Similar systems have also been used in portable instruments [56]. A micro-ISFET was constructed for intracellular determination of K [53]. 

Chemical and Genetic Probes—Nanotube-tipped atomic force microscopes can trace a strand of DNA and identify chemical markers that reveal DNA fine structure. A miniaturized sensor has been constructed based on coupling the electronic properties of nanotubes with the specific recognition properties of immobilized biomolecules by attaching organic molecules handles to these tubular nanostructures. In one study, the pi-electron network on the CNT is used to anchor a molecule that irreversibly adsorbs to the surface of the SWNT. The anchored molecules have a tail to which proteins, or a variety of other... 

The studies prove the suitability of ketocyanine dyes as chromoionophores in plasticized PVC membranes and exploit their features by using them as recognition reagents of IWAO devices to provide miniaturized sensors with an enhanced performance. 

War 05] Wameke, Brett, Miniaturizing sensor networks with MEMS, in Handbook of Sensor Networks Compact Wireless and Wired Sensing Systems, edited by Mohammad Ilyas and Imad Mahgoub, CRC Press LLC, 2005. 

Recent developments in sensor technology allow to create different integrated and miniaturized sensor arrays. Using microsystemtechnology fluidics can be added creating whole micro-analytical devices on chip. However, there are drawbacks involving inappropriate sensor function in media and production. Using sophisticated sensor construction and microfluidics such drawbacks can be overcome. In this chapter different sensor systems and whole micro-analytical devices are presented with emphasis on their applications. 

Keywords Integrated miniaturized sensor arrays, microfluidics, biosensors, microelectronic, microsystemtechnology. 

It is not surprising that the first integrated and miniaturized sensor systems were developed for investigating biological systems and especially the most complex system - the brain [ 1 ]. 

The biosensing devices focus mainly on affinity principles such as antibody -antigen reactions and are based on surface plasmon resonance [25], grating couplers[26] or interferometers [27]. It seems possible to get stable and highly sensitive devices based on these principles [28], and further investigations can lead to miniaturized sensor modules with reduced cost, size and complexity. 

Modified microelectronic technology has created integrated and miniaturized sensor arrays. Additionally, microsystem technology allows to form whole microanalytical systems with integrated fluidics. 

Recent development in multilayer sensor architecture using sequential electrochemical polymerization of pyrrole and pyrrole derivatives to entrap enzymes was tested on a tyrosinase-based phenol sensor [127]. A phenothia-zine dye, thionine served as redox mediator and was covalently attached to the thin, functionalized first polypyrrole layer on Platinum disk electrodes. Then, a second layer of polypyrrole with entrapped tyrosinase was electrochemically deposited. The phenol sensor constructed in this manner effectively transferred electron from enz3Tne to the electrode surface. As all steps in preparation, including deposition of the enzyme-containing layer are carried out electrochemically, this technique may prove to be applicable for mass production of miniature sensors. 

Finally, it should be noted that the recent development of so-called third generation biosensors to achieve direct electron transfer from redox enzyme, oxidoreductase to the electrode without mediators, but through a series of enzyme cofactors or conductive polymers to transfer electrons from the enzyme redox center to the electrode surface [161-164]. This concept with the current technology for preparing miniature sensors with nanotechnology is of great interest to many researchers trying to develop practical sensors in clinical, environmental and industrial analysis. Whether with mediators or without, research for optimum sensor development for various purposes will be intensive in the future. 

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