Optical fiber biosensors preparation

An NIR biosensor coupled with an NIR fluorescent sandwich immunoassay has been developed. 109 The capture antibody was immobilized on the distal end of an optical fiber sensor. The probe was incubated in the corresponding antigen with consecutive incubation in an NIR-labeled sandwich antibody. The resulting NIR-labeled antibody sandwich was excited with the NIR beam of a laser diode, and a fluorescent signal that was directly proportional to the bound antigen was emitted. The sensitivity of the technique increased with increasing amounts of immobilized receptor. There are several factors involved in the preparation of the sandwich type biosensor. A schematic preparation of the sandwich optical fiber is shown in Figure 7.14. 

In 1989, to the best of our knowledge, the first report appeared on the use of an avidin-biotin system for the immobilization of enzymes in the preparation of biosensors. Walt et al. have immobilized biotin-modified enzymes (urease, esterase, and penicillinase) on the surface of biotin-modified optical fiber using avidin as a binder (Figure 5a). They have demonstrated the general use of this procedure in immobilizing several types of enzymes. At nearly the same time, Gunaratna and Wilson used an enzyme column in which choline esterase and choline oxidase were immobilized through avidin-biotin complexation for the determination of acetyl-... 

Similar optical biosensors have been prepared for many other analytes. For example, a cholesterol optical biosensor has been devised based on fluorescence quenching of an oxygen-sensitive dye that is coupled to consumption of oxygen resulting from the enzyme-catalyzed oxidation of cholesterol by the enzyme cholesterol oxidase. Serum bilirubin has been detected using bilirubin oxidase, coimmobilized with a ruthenium dye, on an optical fiber.The bilirubin sensor was reported to exhibit a lower detection limit of iO Xmol/L, a linear range up to 30mmol/L, and a typical reproducibihty of 3% (CV), certainly adequate for clinical application. 

There were five steps involved in the preparation of the optical fibers tapering, cleaning, silanization, crosslinker attachment, and covalent binding of antibodies. The procedures used were based on methods outlined previously (Bhatia et al., 1989 Ogert et al., 1992). The goal was to immobilize affinity purified antibodies on the surface of the fibers for the capturing of complex molecules in solution and ultimately detection using the biosensor. 

Recently, LSPCF fiber-optic biosensors are used in clinical diagnosis for alpha-fetoprotein (AFP) identification in human serum. Figure 8.28 shows the relationship between the fluorescent signals and the AFP concentrations of human serum measured by ELISA system (ABBOTT, ARCHITECT i-2000). The preparation and the measurement of human serum were completed at Taipei City Hospital (Taipei, Taiwan), The correlation coefficient R is 0.9331. 

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