Sensor development

The use of DRIFTS for the characterization of surfaces has to date been limited, but has recently been used for applications in fields as diverse as sensors development [12], soils science [13], forensic chemistry [14], corrosion [15], wood science [16] and art [F7]. Given that there is in general no reason for preferring transmission over difilise reflectance in the study of high-area powder systems, DRIFTS is likely to become much more popular in the near fiiture. 

Chemielabor auf dem Mikrochip, Blick durch die Wirtschafi, May 1997 Lab-on-a-chip protein separation DuPont s investigations general advantages of pTAS DARPA foundation of military biological sensor development MEMS components [223]. 

Special optical fibres have been intensively investigated during recent years because of their potential wide-range use for on-line monitoring of material properties or processes in a number of areas of human activity (environment protection, food industry, medicine etc.) Their technology can be considered an integral part of the team-work on optical fibre sensors development. Despite special optical fibres represent a unique and often indispensable tool for a variety of sensor applications, special fibre production still represents only a small fraction of the market. Probably it is because of their low consumption (in comparison with standard telecommunication fibres), the need for much more advanced know-how and lower reproducibility. 

The interdisciplinary nature of optical chemical sensors opens a variety of new directions in sensor development. The issue of chemical selectivity is... 

After discussing various sensitive layers later, both principles will be applied to monitor effects in biomolecular or chemical sensitive layers. The applications will demonstrate the feasibility of the methods as well as their advantages and their disadvantages. Therefore various applications are given, sometimes even for the same analyte, in order to demonstrate the normal approach in sensor development to select the best transduction principle for a specific application. 

As it is shown in Figure 8, the enzyme can be immobilized in the vicinity (membrane, beads, etc) or on the surface of the fiber for optical fiber sensor development. Alternatively, it can be placed in a reactor and use the optode... 

The achievements in optical detection techniques and the interest in the sol-gel process for creation of new materials, are leading to developing of various sensors. The majority of reported sensors developments have concentrated on the use of thin films. There are many reasons for this. The important one is the susceptibility of monoliths to cracking due to internal stresses, particularly when exposed to liquid penetration. More attractive are... 

Center for Healthcare Technologies at Lawrence Livermore National Laboratory in Livermore, potentially capable to measure pH at or near the stroke site29. The probe is the distal end of a 125 pm fibre tapered up to a diameter of 50 pm. A fluorescent pH-indicator, seminaphthorhodamine-1-carboxylate, is embedded inside a silica sol-gel matrix which is fixed to the fibre tip. Excitation of the dye takes place at 533 nm and the emission in correspondence of the acid (580 nm) and basic (640 nm) bands are separately detected. The use of this ratiometric technique obviates worrying about source fluctuations, which have the same effects on the two detected signals. The pH sensor developed was first characterised in the laboratory, where it showed fast response time (of the order of tens of seconds) and an accuracy of 0.05 pH units, well below the limit of detection necessary for this clinical application (0.1 pH units). The pH sensor was also tested in vivo on rats, by placing the pH sensor in the brain of a Spraque-Dawley rat at a depth of approximately 5 mm30. 

Other optodes have been developed and tested in-vivo, all of them using a fluorophore, the fluorescence of which is quenched by oxygen. In the intravascular sensor developed by CDI, previously described, a specially synthesised fluorophore, a modified decacyclene ( Lexc=385 nm, em=515 nm), is combined with a second reference-fluorophore that is insensitive to oxygen, and is incorporated into a hydrophobic silicon membrane that is permeable to oxygen. 

Figure 11. Photo of the prototype of the glucose sensor developed by Lifetrac.

Some examples of common materials developed for oxygen sensing are given in Table 1. The top part of Table 1 describes general purpose sensors, while the bottom part is concerned with specialized PtOEPK-PS based sensors developed for food packaging. 

F. Caruso, E. Rodda, D.F. Furlong, K. Niikura, and Y. Okahata, Quartz crystal microbalance study of DNA immobilization and hybridization for nucleic acid sensor development. Anal. Chem. 69, 2043-2049 (1997). 

Metal/metal oxides are the materials of choice for construction of all-solid-state pH microelectrodes. A further understanding of pH sensing mechanisms for metal/metal oxide electrodes will have a significant impact on sensor development. This will help in understanding which factors control Nemstian responses and how to reduce interference of the potentiometric detection of pH by redox reactions at the metal-metal oxide interface. While glass pH electrodes will remain as a gold standard for many applications, all-solid-state pH sensors, especially those that are metal/metal oxide-based microelectrodes, will continue to make potentiometric in-vivo pH determination an attractive analytical method in the future. 

Micro- (and even nano-) electrode arrays are commonly produced with photolithography and electronic beam techniques by insulating of macro-electrode surface with subsequent drilling micro-holes in an insulating layer [136, 137], Physical methods are, however, expensive and, besides that, unsuitable for sensor development in certain cases (for instance, for modification of the lateral surface of needle electrodes). That s why an increasing interest is being applied to chemical approaches of material nanostructuring on solid supports [140, 141],... 

As a result of sensor development in the automotive industry, low-priced acceleration sensors are now available. Acceleration sensors are fundamentally also suited to observing excursion (Fig. 5.57) of the suds container caused by imbalance. However, static measurement of the weight of the washing, as achieved with a distance sensor, is not possible with acceleration sensors. 

Climate Control Current and Future Sensor Developments... 

The chemical inertness and optical transparency of Si02 sol-gel matrices make the doping methodology ideal for sensor developments, even if leaching is an issue that must be often addressed. Another attractive, unique feature is that non-toxic sol-gel silicas can be made in... 

Figure 6.10 Non-invasive glucose sensor developed by TheraSyn Sensors Inc. will reach the market within the next two years. (Image courtesy of Prof. F. Y. Bright.)...

Given the tremendous development of SAMs over the past two decades it is dear that this chapter is able to cover only a fraction of the spectrum of topics related to the combination of SAMs and electrochemistry. For a comprehensive picture the reader is referred to a number of additional review articles, one of which is the excellent and extensive account of organized monolayers on electrodes by Finklea [23]. Besides this one, which comprehensively covers the literature up to the mid-1990s, other more focused reviews are available that address various developments over the past decade in areas of sensor development and electroanalytical applications [22, 24—28] and electrochemical metal deposition on SAM-modified electrodes [29, 30]. 

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