Fluorescence immunosensors

The applications of visible fluorescent immunosensors described are all susceptible to large interferences from biomolecules such as bilirubin and porphyrins. A more comprehensive review of immunosensors has been published by Robinson.(10S) The spectral interferences associated with visible fluorophores have prompted the design of an NIR optical immunosensor techniques with high sensitivity and low interference. 

The use of enzyme labels in ELIS A-type immunosensors and simple amperometric detection schemes resulted in simple and cost-effective alternatives to fluorescence immunosensors. In particular, the use of alkaline phosphatase as enzyme label allowed for the fabrication of advanced immunosensors with signal amphfi-cation by means of redox cycling, which has been a success story of its own. This detection scheme has been used in immunosensors and other biosensors and has stimulated significant developments in electrode fabrication. Instrumental electroanalysis, namely capacitance measurements and EIS allow for label-free detection of immunoreactions. 

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

A fiber optic immunosensor (FOI) has also been reported for detection of PCBs in Aroclors [204]. The quartz fiber surface is coated with PAbs against PCBs and the competitive assay takes place using as fluorescent tracer, an analog of the analyte coupled to 2,4,5-trichlorophenoxybutyrate (TCPB) on the Ab-coated fiber. The LOD achieved is around 10 pg L L... 

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. 

Tatsu et a/.(106) reported a novel immunosensor using immobilized liposomes doped with carboxyfluorescein and dinitrophenyl (DNP) hapten on the tip of an optical fiber. On complement-mediated immunolysis by anti-DNP-antibody, the fluorescent signal of the liberated carboxyfluorescein was measured. 

A reversible, direct fluoroimmunosensor for human serum albumin (HS A) measurement has been described by Bright et al.(m> Antibody Fab fragments are first immobilized on small quartz plates by hinge-region thiols, and then dansylated. The immunosensor is formed by attaching the quartz plates with bound Fab to the distal end of a bifurcated fiber-optic probe, which transmits both the excitation and emission. Binding of ffSA to the immunosensor results in a three- to five-fold enhancement of dansyl fluorescence. The sensor can be reused up to 50 times, with a detection limit of about 1.8 x 10-8 M, and a somewhat limited dynamic range. 

An optical immunosensor for continuous T4 measurement has been described, in which the fluorescent indicator protein is separated from the sample flow chamber by a dialysis membrane.024) The indicator is T4-binding globulin (TBG), the intrinsic fluorescence (ex. 290 nm) of which is quenched by T4binding. Due to the high affinity of the TBG for thyroxine, the immunosensor is not reversible, but multiple measurements can be made until the TBG is saturated. Sensitivity is inadequate for clinically useful concentrations of T4, but suggestions for improvement of the method are made. 

Keywords Biosensors Dyes Fluorescence Glass Immunosensors Luminescence Nanocomposites Optodes Optosensors Ormosils PVC Silica Siloxanes Sol-gel... 

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