Microsensors

Microsensor Microsensors Microsil Microsmatic Microsoft Microspheres... 

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. 

Kolesar ES, Brothers CP, Howe CP, et al. 1992. Integrated-circuit microsensor for selectively detecting nitrogen-dioxide and diisopropyl methylphosphonate. Thin Solid Films 220(1-2) 30-37. 

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... 

Extensive work has been carried out on microsensors built from electropolymerized nickel porphyrin films.328,329 Films of Prussian blue (Fe4[Fe(CN)6]3) 345 metal-salen complexes (M = Co, Fe, Cu, Mn)346 or the ferrocene-containing Nin-tetraaza[14] annulene (24),347 also exhibit interesting activity for NO electrooxidation and sensing. 

The experimental set-up for cellular oxygen measurements (p02) consists of following components p02 measuring micro chamber (volume 0.6 microliter), polarographic microelectrode, water-bath for constant temperature, chemical microsensor connected to a strip-chart recorder and gas calibration unit. 

Among the non-medical sensors, those for oil contamination and for oxygen are predominant. Fig. 6 shows the tip of the fiber optic oxygen microsensor of Presens. 

Figure 6. Tip of the 20-pm tip of a fiber optic oxygen microsensor. The tip is coated with a ormosil-type of sol-gel doped with a ruthenium indicator for oxygen that display red luminescence. The sensor measures its decay time as a function of oxygen partial pressure.

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

Song A., Parus S., Kopelman R., High-performance fiber-optic pH microsensors for practical physiological measurements using a dual-emission sensitive dye, Anal. Chem. 1997 69 863. 

Park J., Groves W.A. and Zellers E.T., Vapor Recognition with Small Arrays of Polymer-Coated Microsensors. A Comprehensive Analysis, Anal Chem 1999 71 3877-3886. 

Figure 1.3 shows a typical calibration curve generated using an NO microsensor and the SNAP method described. 

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). 

T. Malinski, F. Bailey, Z.G. Zhang, and M. Chopp, Nitric-oxide measured by a porphyrinic microsensor in rat-brain after transient middle cerebral-artery occlusion. J. Cereb. Blood Flow Metab. 13, 355-358 (1993). 

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