Optical immunoassay

In order to investigate this effect, ordered arrays of metallic nano-islands were fabricated on glass substrates by a process of natural lithography using monodisperse polystyrene nanospheres. The metal particle dimensions were tailored in order to tune the plasmon resonance wavelength to match the spectral absorption of the fluorophore. The fluorophore, Cy5 dye, which is widely used in optical immunoassays and has a medium quantum efficiency ( 0.3), was used in this preliminary study of the plasmonic enhancement effect. 

An example of an evanescent wave fiber optic immunoassay and the associated optics has been described in detail for measurement of anti-rabbit IgG.(130) Rabbit antibody is immobilized on the distal face of an optical fiber. Unlabeled anti-rabbit IgG competes with fluorescein-labeled anti-rabbit IgG for rabbit antibody binding sites... 

J. F. Place, R. M. Sutherland, and C. Dahne, Opto-electronic immunosensors A review of optical immunoassay at continuous surfaces, Biosensors I, 321-353 (1985). 

Before an analytical measurement can be made, it is necessary to separate bound drug from unbound drug in radioimmunoassays and also, if the highest sensitivity is required, in optical immunoassays. 

Optical immunoassays have a number of advantages over radioimmunoassays (Table 3), mainly because the reagents are stable and homogeneous assays can be produced simply. Various labels can... 

Table 3. Comparison of radioimmunoassays and homogeneous optical immunoassays...

Commercial optical immunoassays are usually homogeneous, but for the highest sensitivity, separation of bound drug from unbound drug is required. 

The effect of temperature on enzyme immunoassays should not be overlooked, and adequate thermo-static control is mandatory. This problem is not met with in other optical immunoassays which gives the latter some advantages. 

The final measurement can contribute considerably to imprecision and for optical immunoassays is instrument-related. For radioimmunoassays, considerable improvements in both time and precision may be made by employing y-labelled drugs and counting in a 16-head y-counter. Scintillation counters have an accuracy of measurement which is approximately the square root of the total number of counts, e.g. about 1% counting error when measuring 10000 counts. 

Homogeneous optical immunoassays are easily automated, and instrumenls specificquality control data held in mi< processors. 

Figure S 2-6 Schematic diagram of the principles of an optical immunoassay (OiA ) using thin film detection. (Courtesy Thermo Electron Corporation, Louisville, CO.)...

Fries SM. Diagnosis of group A streptococcal pharyngitis in a private clinic comparative evaluation of an optical immunoassay method and culture. J Pediatr 1995 126 933-6. 

A no-label, homogeneous, optical immunoassay for human IgG has been developed and tested [94] (Figure 18-26). Following adsorption of antiserum to the surface of an optical waveguide, the immobilized antibody was then reacted with a solution containing antigen. The... 

Fluorescence-based fiber optic immunoassay (a) 100 pg/mL (b) 1 ng/mL (a) Buffer solution (b) River water... 

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