Immunosensors fluorescence-based

Endo, T., A. Okuyama, Y. Matsubara, et al. 2005. Fluorescence-based assay with enzyme amplification on a micro-flow immunosensor chip for monitoring coplanar polychlorinated biphenyls. Anal. Chim. Acta 531 7-13. 

Engstrom HA, Andersson PO, Ohlson S (2006) A label-free continuous total-intemal-reflection-fluorescence-based immunosensor. Anal Biochem 357 159-166 Sapsford KE, Rasooly A, Taitt CR et al (2004) Detection of Campylobacter and Shigella species in food samples using an array biosensor. Anal Chem 76 433 140 Sapsford KE, Taitt CR, Loo N et al (2005) Biosensor detection of botulinum toxoid A and staphylococcal enterotoxin B in food. Appl Environ Microbiol 71 5590-5592... 

Fluorescence and chemiluminescence sensors are considered the most sensitive in the class of optical sensors. They have a higher selectivity because the chemiluminescent and fluorescent reactions take place in certain medium conditions, and only a limited group of ions and molecules can be involved. When the selectivity of this type of sensor is not sufficient, the quality of analysis can be improved by using a biochemical reaction such as an enzymatic reaction (chemiluminescence- or fluorescence-based biosensors) or an immunoreaction (chemiluminescence- or fluorescence-based immunosensors). By using these types of optical sensors the chemical analysis becomes most sensitive and selective.265... 

One example of a nice commercial immunosensor is produced by Serono Diagnostics. This fluorescence-based evanescent-wave immunosensor [374], [375], [376] incorporates a novel capillary-fill design, and is shown in Figure 83. 

Some of the inherent difficulties associated with the use of this fluorescence-based immunosensor include fiber to fiber variability in the signal, cost of the instrument as well as fibers, and availability of portable commercial instrument. Still, further characterization of the instrument and the methods surrounding the immunoassay are necessary in order to increase its potential application as a sophisticated analytical technique. Relevant to the detection of botulinum neurotoxins, binding in a variety of biological and environmental matrices needs to be investigated. Also, to increase the applicability of the biosensor as a technique that offers reliable quantitative results, a method for internal standardization should be investigated. The fiberoptic immunosensor in its present state is best described as a technique that allows for the selective detection and monitoring of botulinum neurotoxins at concentrations at or above 300 pg/mL. However, this technique would provide only semi-quantitative results as far as the determination of unknown concentration of the toxin is concerned. 

S. Aoyagi and M. Kudo, Development of fluorescence change-based, reagent-less optic immunosensor. Biosens. Bioelectron. 20, 1680-1684 (2005). 

An immunosensor based on a competitive fluorescence energy-transfer immunoassay was reported by Anderson 105) for the measurement of phenytoin. Texas red-labeled antibody was incubated with a phenytoin derivative. On displacement of the derivative by the antigen, the change in the fluorescence signal was recorded. Detection limits approached 5 /iM with response times ranging from 5 to 30 min. 

To demonstrate a way of the use of aptamers in design of biomimetic sensors, two examples will be cited from the recent literature. The piezoelectric sensor for protein IgE has been developed with the use of commercially available anti-IgE aptamer oligonucleotide.167 The obtained sensor shows specificity and sensitivity equivalent to these of immunosensor, but for aptamer-based sensor a less decrease of sensitivity after consecutive cycles of analyte binding and regeneration, as well as relative heat resistance and stability over several weeks was shown. A more complex mechanism of sensing was employed in adenosine aptamer-based sensor.168 Detection was based on enzymatic activity measurements by fluorescence polarization with the use of aptameric enzyme subunit, which was a DNA aptamer composed of enzyme-inhibiting aptamer and adenosine-binding aptamer. 

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