Sensing oxygen

Use of collisional quenching as the sensing mechanism requires the fluorescent probe to be sensitive to quenching by the desired analyte. Collisional quenching results in a decrease in intensity and lifetime, which can be described by the Stem-M Imerequatii , 

The Clark electrode is widely used because it is the best available technique to date. There are a number of limitations and problems in its use that exist and it is important to be aware of these. We have briefly summarized the most critical ones and for greater details the reader is directed to the excellent review by Lee and Tsao.(l) 2 3 4 5 

Long-term stability. The polarographic Clark electrode utilizes an electrolyte that is eventually consumed. Consequently, long-term use (several days) results in gradual drift in the electrode signal due tn electrolyte consumption. 

Response time. In the literature, response time is usually specified as the time taken for the electrode to reach 90% of the output. Typical response times are around 30 sec. A fast response time is critical when one is measuring transient phenomena such as oxygen respiration rates in tissue or suspended cells and dynamic measurements of the volumetric mass transfer coefficient in bioreactors. 

Sensitivity. Since terminal oxidases have high affinities for oxygen, low-level pCL measurements are important. The signal-to-noise ratio may be unacceptable in some situations. 

Electrical interference. When low-level electrical signals are measured, it is very likely that substantial error may be introduced in the measurement by extraneous 

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Cholesterol The end point for the cholesterol reaction can be determined by following dye formation. Additionally, the amount of oxygen consumed can be measured amperometricaHy by an oxygen-sensing electrode (see Electro analytical techniques). The H2O2 produced by cholesterol oxidase requires phenol to produce dye. 

In addition to the method described above, there are at present, on the market, several glucose analyzers offered by several commercial companies, wherein the individual injects approximately 20 microliters of serum. This is then incubated with glucose oxidase and the peroxide or oxygen generated is measured with an oxygen sensing electrode. These instruments cannot perform the test on 1 xl nor are they designed for that purpose at the present time. 

Butler 1989 oxygen sensing via reflectivity of nickel film... 

Papkovsky D.B., Ponomarev G.V., Trettnak W., Oleary P., Phosphorescent Complexes of Porphyrin Ketones - Optical Properties And Application to Oxygen Sensing, Anal. 

Lee S., Okura I., Porphyrin-doped sol-gel glass as a probe for oxygen sensing, Anal. Chim. Acta 1997 342 181-188. 

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. 

Table 1. Common materials used in quenched-fluorescence oxygen sensing (Ru(dpp)3(C104)2 tris(diphenylphenantroline) ruthenium(II) perchlorate PtOEPK platinum(II)-octaethyl-porphine-ketone PtPFPP platinum(II)-tetrakis(pentafluorophenyl)porphine PS.poly(styrene), PSu poly(sulfone) PSB poly(styrene-butadiene) block co-polymer PVC polyvinylchloride) APET amorphous poly(ethyleneterephthalate) PE poly(ethylene).

Fitzgerald M., Papkovsky D.B., O Sullivan C.K., Guilbault G.G., Optical oxygen sensing in vacuum packed foods, Proc. workshop Biosensors for Environmental Monitoring, Kinsale, Ireland, 12-15 May, 1998, p.89. 

Papkovsky D.B., Methods in optical oxygen sensing protocols and critical analyses, Methods Enzymol., Ed., C.K.Sen, G.L.Semenza, 2004, 383, 715-734. 

M.H. Schoenfisch, K.A. Mowery, M.V. Rader, N. Baliga, J.A. Wahr, and M.E. Meyerhoff, Improving the thromboresistivity of chemical sensors via nitric oxide release fabrication and in vivo evaluation of NO-releasing oxygen-sensing catheters. Anal. Chem. 72, 1119—1126 (2000). 

I. Klimant and M. J. P. Leiner, Recent investigations in optical oxygen sensing The behavior of ruthenium complexes in silicone matrices, in Abstracts, 1st European Conference on Optical Chemical Sensors and Biosensors, Graz, Austria, April 12-15, 131 (1992). 

J. R. Alcala, C. Yu, and G. J. Yeh Digital phosphorimeter with frequency domain signal processing application to real time fiber optic oxygen sensing, Rev. Sci. Instrum. 64, 1554-1560 (1993). 

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