Energy-transfer fibers

Figure 14.18. Diagrammatic representation of a phenytoin fluorescence energy transfer fiber optic sensor, as described in the text. -< = Antibody-Texas Red P = unlabeled phenytoin P = phenytoin-b-phyco-erythrin. (Adapted from Ref, 119.)...

Energy transfer fibers are based on the principle that, upon excitation, a donor molecule wUl transfer a portion of its energy to an acceptor molecule if there is overlap between the donor s emission and the acceptor s absorption spectrum. This transfer occurs without the emission of a photon and is primarily the result of a dipole-dipole Interaction between the donor and acceptor. The efficiency of singlet dlpde-dipoie energy transfer is predicted by Forster theory (27). 

More recently, the method of scanning near-field optical microscopy (SNOM) has been applied to LB films of phospholipids and has revealed submicron-domain structures [55-59]. The method involves scanning a fiber-optic tip over a surface in much the same way an AFM tip is scanned over a surface. In principle, other optical experiments could be combined with the SNOM, snch as resonance energy transfer, time-resolved flnorescence, and surface plasmon resonance. It is likely that spectroscopic investigation of snbmicron domains in LB films nsing these principles will be pnrsned extensively. 

The upgrade of a frequency-domain fluorescence lifetime imaging microscope (FLIM) to a prismless objective-based total internal reflection-FLIM (TIR-FLIM) system is described. By off-axis coupling of the intensity-modulated laser from a fiber and using a high numerical aperture oil objective, TIR-FLIM can be readily achieved. The usefulness of the technique is demonstrated by a fluorescence resonance energy transfer study of Annexin A4 relocation and two-dimensional crystal formation near the plasma membrane of cultured mammalian cells. Possible future applications and comparison to other techniques are discussed. 

There are several works published on pH sensors based on energy transfer. Jordan and Walt developed a single-fiber optic sensor based on... 

Jordan D.M., Walt D.R., Milanovich F.P., Physiological pH fiber-optic chemical sensor based on energy transfer, Anal. Chem. 1987 59 437-439. 

A. Sherman and O.S. Wolfbeis, Fiber optic fluorosensor for sulfur dioxide based on energy transfer and exdplex quenching, Proc. SPIE, 990 (1989) 116. 

D. Meadows and J. S. Schultz, Fiber-optic biosensors base on fluorescence energy transfer, Talanta 35, 145-150 (1988). 

P. Yuan, D. M. Jordan, F. P. Milanovich, and D. R. Walt, Fiber-optic chemical sensors based on energy transfer, SPIE Proc. 906, 28-29 (1988). 

A phenytoin energy transfer immunosensor has been reported that is reversible and direct, in which macromolecular reagents are retained within a short length of 200-/dialysis tubing cemented to the end of an optical fiber (Figure 14.18).018 119)A... 

An energy transfer immunosensor described for IgG measurement exploits controlled release of donor and acceptor from ethylene-vinyl acetate copolymer plugs positioned in opposite ends of a cylindrical reaction chamber (Figure 14.19).(122) Fluorescein-antibody donor and Texas Red-antigen-IgG acceptor are continuously released from the polymeric plugs. The reagents diffuse to the center of the cylindrical reaction chamber, where a perpendicular top-mounted optical fiber delivers the excit-... 

Meadows DL, Schultz JS. Design, manufacture and characterization of an optical fiber glucose affinity sensor based on an homogeneous fluorescence energy transfer assay system. Analytica Chimica Acta 1993, 280, 21-30. 

Fiber-optic sensors based on controlled-release polymers provide sustained release of indicating reagents over long periods. This technique allows irreversible chemistries to be used in the design of sensors for continuous measurements. The sensor reported in this paper is based on a fluorescence energy transfer immunoassay. The sensor was cycled through different concentrations of antigen continuously for 30 hours. 

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