Optical fiber biosensors fluorescence

Fig. 5.4. Optical Fiber biosensor, (a) Extrinsic optical fiber is used for the guiding the light to and from the sensor area, (b) Intrinsic the receptor molecules are immobilized on the fiber core after decladding of the fiber. The detection is based on fluorescence labels.

Fig. 4 - An optic fiber biosensor for cocaine using a mAb against benzoylecgonine as the biological sensing element, (left) The time course of binding of FL-BE to the mAb-coated fiber expressed by the fluorescent signal transmitted via the fiber. After reaching steady state, FL-BE was withdrawn from the flow buffer (indicated by the arrow). The bound FL-BE dissociated and fluorescence decreased exponentially, (right) Reusability of the biosensor for multiple assays of cocaine introduced into the flow buffer after steady-state fluorescence (200 mV) was achieved. Cocaine at the indicated concentrations was added to the flow buffer for only the time intervals indicated by the bars. The downward deflection resulted from displacement of FL-BE by cocaine, but upon removal of cocaine from the flow buffer FL-BE displaced the bound cocaine. Reproduced with permission from reference 4, Copyright 1995 American Chemical Society.

A biosensor has been demonstrated based on acrylodan-labeled bovine serum albumin immobilized on a silica optical fiber. The fluorescence behavior of the sensor changes in the environment of ionic surfactants. It was shown to be elfective in the 5-60 micromolar surfactant range (107). 

The dye is excited by light suppHed through the optical fiber (see Fiber optics), and its fluorescence monitored, also via the optical fiber. Because molecular oxygen, O2, quenches the fluorescence of the dyes employed, the iatensity of the fluorescence is related to the concentration of O2 at the surface of the optical fiber. Any glucose present ia the test solution reduces the local O2 concentration because of the immobilized enzyme resulting ia an iacrease ia fluorescence iatensity. This biosensor has a detection limit for glucose of approximately 100 ]lM , response times are on the order of a miaute. 

W. Trettnak, O.S. Wolfbeis, A fully reversible fiber optic lactate biosensor based on the intrinsic fluorescence of lactate monooxygenase, Fresenius Z. Anal. Chem. 1989, 334, 427. 

A biosensor was designed where a dehydrogenase and an enlarged coenzyme are confined behind an ultrafiltration membrane. The amino acid is determined indirectly, by measuring the fluorescence of the reduced coenzyme (kex 360 nm, kfl 460 nm) produced in reaction 22, with the aid of an optical fiber. The coenzyme is regenerated with pyruvate in a subsequent step, as shown in reaction 23. This biosensor was proposed for determination of L-alanine and L-phenylalanine for monitoring of various metabolic diseases and for dietary management363. 

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. 

Several papers have been published in which, instead of concentrating on specific reactions, the technology was highlighted. One, by Marose et al.,7 discusses the various optics, fiber optics, and the probe designs that allow in situ monitoring. They describe the various optical density probes used for biomass determination in situ microscopy, optical biosensors, and specific sensors such as NIR and fluorescence. 

Optical biosensors typically consist of an optical fiber which is coated with the indicator chemistry for the material of interest at the distal tip (Fig. 22). The quantity or concentration is derived from the intensity of absorbed, reflected, scattered, or re-emitted electromagnetic radiation (e.g. fluorescence, bio- and chemiluminescence). Usually, enzymatic reactions are exploited, e.g. [463]. 

An evanescent wave biosensor was devised for determination of analytes capable of intercalation in dsDNA in a FIA system. A polyethylene lensed optical fiber is coated with a thin polymeric layer containing dsDNA which is immobilized there. The fiber is placed in a FLA system immersed in a solution of ethidium bromide (144), which undergoes intercalation in the dsDNA. The fluorescence signal of 144 is thus enhanced about a 1000-fold relative to the evanescent wave fluorescence measurement without the coating and is dependent on the concentration in solution. If an analyte is present in the same solution, it competes with 144 for intercalation in the DNA and causes fluorescence quenching, which can be measured and correlated to the analyte concentration. This method was applied to determination of various analytes, including 4, 6-diamidino-2-phenylindole dihydrochloride (145)247. 

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. 

TVettnak, W., Wolfbeis, O. S., A Fully Reversible Fiber Optic Lactate Biosensor Based on the Intrinsic Fluorescence of Lactate Monooxygenase , Fresenius Z. AnaL Chem. 334 (1989) 427-430. 

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