In microsensors

Future directions in biosensors will require the miniaturization of individual sensors for in-vivo use, and for use in microsensor arrays (7). Ideally, these biosensors should be capable of direct, rather than differential measurement, and should have reasonable lifetimes. 

Different bonding techniques have been developed for use in microsensors, each owing its popularity to some specific advantages, although none of them meets all the requirements. Only a brief review is given below for detailed information please see [33, 34]. 

For sensors in the automobile environment, mechanical shock load, humidity, elevated temperature, and temperature shock are the main causes of failure. Table 5.9.1 gives an overview of typical failure issues that are most common in microsensors and which need to be considered in reliability studies. 

Below, we indicate the status and trends in microsensor testing and metrology. 

The use of a graphite electrode, particularly glassy carbon, is also relatively limited in microfabricated electrochemical sensors. However, thick-film silk-screened graphite electrodes have been used in chemical sensor development, and the use of carbon fiber in microsensor applications has been reported. The purity of the graphite ink for thick-film silk screening is very critical to the performance of the sensor. 

Gardner J. W., Microsensor array devices, in Microsensors Principles and Applications (Chichester Wiley, 1994), 279. 

MEMS find wide applications in microsensors such as acoustic waves, biomedical, chemical, inertia, optical, pressure, radiation, and thermal microactuators like valves, pumps, and microfluidics electrical and optical relays and switches grippers tweezers and tongs as well as linear and rotary motors, etc., in various fields. They also find application in microdevice components such as palmtop reconnaissance aircrafts, minirobots and toys, microsurgical and mobile telecom equipment, read/ write heads in computer storage systems, as well as ink-jet printer heads [4]. 

The focus in the thin film research impact area is to develop a fundamental understanding of how morphology can be controlled in (1) organic thin film composites prepared by Langmuir Blodgett (LB) monolayer and multilayer techniques and (2) the molecular design of membrane systems using ionomers and selected supported liquids. Controlled structures of this nature will find immediate apphcation in several aspects of smart materials development, particularly in microsensors. 

Strike, D. J., Hengstenberg, A., Quinto, M., Kurzawa, C., Koudelka-Hep, M., Schuhmann, W. Localized visualization of chemical cross-talk in microsensor arrays by using scanning electrochemical microscopy. Mikrochim Acta 1999, 131, 47-55. 

A chemical microsensor can be defined as an extremely small device that detects components in gases or Hquids (52—55). Ideally, such a sensor generates a response which either varies with the nature or concentration of the material or is reversible for repeated cycles of exposure. Of the many types of microsensors that have been described (56), three are the most prominent the chemiresistor, the bulk-wave piezoelectric quartz crystal sensor, and the surface acoustic wave (saw) device (57). 

Electrochemical Microsensors. The most successful chemical microsensor in use as of the mid-1990s is the oxygen sensor found in the exhaust system of almost all modem automobiles (see Exhaust control, automotive). It is an electrochemical sensor that uses a soHd electrolyte, often doped Zr02, as an oxygen ion conductor. The sensor exemplifies many of the properties considered desirable for all chemical microsensors. It works in a process-control situation and has very fast (- 100 ms) response time for feedback control. It is relatively inexpensive because it is designed specifically for one task and is mass-produced. It is relatively immune to other chemical species found in exhaust that could act as interferants. It performs in a very hostile environment and is reHable over a long period of time (36). 

Microsensors have been used to develop profiles in mixed species biofilms. Figure 10 shows concentration profiles of sulfide, oxygen, and pH in a biofilm accumulated on the surface of a mild steel corrosion coupon. The concentration of sulfide is highest near the metal surface, where iron sulfide forms quickly and covers the steel surface if both ferrous and sulfide ions are available. At low ferrous ion concentrations, adherent and temporarily protective films of iron sulfides are formed on the steel surface, with a consequent reduction in corrosion rate. High rates of SRB-induced corrosion of mild steel are maintained only in high concentrations of ferrous ion. 

Methods exist for determining levels of diisopropyl methylphosphonate in air, soil, and water. These methods include separation by GC coupled with FID and flame photometric detection (FPD), determination by infrared and Raman spectroscopy, separation by ionization mass spectrometry, determination utilizing piezoelectric crystals, and determination by gas-sensitive microsensors. Table 6-2 summarizes the methods that have been used to analyze environmental samples for diisopropyl methylphosphonate. 

There is an increasing interest in the development of electrochemical sensors and microsensors for detecting and monitoring NO or N02, due to their importance in clinical and environmental analysis. It has been suggested that transition metal electrocatalysts active for NO or N02 coordination and reduction could be exploited for the development of metal-complex film electrodes for N02 and NO sensing. However, most of the sensory devices reported so... 

Klimant I., Meyer V., Kuhl M., Fiber-optic oxygen microsensors, a new tool in aquatic biology, Limnol. Oceanography 1995 40 1159. 

Simonsen s group has performed some elegant work over the years on NO release characteristics from rat superior mesenteric artery. Initially, Simonsen s group simultaneously monitored artery relaxation and NO concentration in the artery using a NO microsensor in response to various drugs [120], NO concentration was monitored via an ISONOP30 electrode, purchased from WPI and inserted into the artery lumen using... 

T. Malinski, Z.Taha, S. Grunfeld, A. Burewicz, P. Tomboulian, and F. Kiechle, Measurement of nitric oxide in biological materials using a porphyrinnic microsensor. Anal. Chim. Acta 279, 135—140 (1993). 

T. Malinski and Z. Taha, Nitric-oxide release from a single cell measured in situ by a porphyrinic-based microsensor. Nature 358, 676-678 (1992). 

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