Immunoreactors

The determination of antigens and antibodies can be improved by immobilization of the appropriate immunochemical partner of the analyte. When the immunological reaction can be rendered reversible the immobilized ligand becomes reusable. Whereas in immunoreactors the immunosorbent is separated from the sensor, in immunosensors both elements are in intimate physical contact. We shall show below that these devices can be used to perform the classical functions of immunoassays. 

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Fig. 3 Generic FIIA system. A heterogeneous format is shown. The antibodies are immobilized in the immunoreactor. The analyte and the labeled Ag (in this case with an enzyme) are passed through the system and the competition step takes place. The flow of the substrate solution through the system allows the determination of the amount of bound labeled Ag, which is then detected and measured...

Digoxin Immunoreactor, immobilized antibodies, acridin-ium ester-H202 CL 0.2 ng/mL 102... 

HPLC is ideally suited to examine adsorption kinetics in the working conditions of column immunoassays. In this technique, high flow rates and minimized column volumes are required to perform rapid on-line immunodetections. The column capacities and residence times in the column are parameters that influence the efficiency of the immunoreactor. Kinetic studies using the chromatographic format will be useful to understand the process better and optimize the methodology. 

An amperometric immunosensor using sequential injection analysis techniques to detect the herbicide 2,4-D in water was described by Wilmer and Trau [102,103]. This rapid competitive EIA used an alkaline phosphatase-labelled monoclonal antibody directed against the herbicide and an immunoreactor with 2,4-D immobilized via BSA, either to Eupergit in a column or directly to the surface of a glass capillary. A detection limit of the immunosensor at 0.1 (jLg 2,4-D 1, without enrichment of the analyte, pointed to the feasibility of making automatic measurements of 2,4-D in drinking and ground water. 

DA Palmer, et al. Flow injection electrochemical enzyme immunoassay for theophylline using a protein-A immunoreactor and /t-aminophenyl phosphate// -aminophenol as the detection system. Analyst 117 1679, 1992. 

Chemiluminescence continues to be a very selective and sensitive detection tool in FIA immunoassays. The main component in the most commonly used heterogeneous systems is an immunoreactor column, consisting of PTFE tubing packed with immobilized antibodies or haptens. The immunoreac-tion and the chemiluminescence reaction takes place within the immunoreactor, and the emitted light is collected directly from the cell. 

As the antibodies are immobilized and the immunoreactor can be used repeatedly, the consumption is minimum on the other hand, the binding reaction also represents a preconcentration of the sample, and pretreatment is usually not necessary. 

The simplest setup consists of a peristaltic pump, an injection valve, the immunoreactor, and a detector. For special purposes multichannel pumps and valve switching systems have been developed. Sample and all reagents are injected into a flowing stream and transported to the immunoreactor where binding to the immobilized antibodies (or antigens, respectively) takes place. Detection is carried out either... 

Chiem, N.H. Harrison, D. Microchip systems for immunoassay An integrated immunoreactor with electrophoretic separation for serum theophylline determination. J. Clin. Chem. 1998, 44, 591. 

Combination of immunoassay and microfluidic platforms offers advantages related to the selectivity and sensitivity, associated to the antigen-antibody interaction with the remarkable features stated above for microfluidic platforms. Microfluidic immunoassays make use of a network of microchannels and/or immunoreactor chambers usually built in a monolithic platform (similar or even the same designs used in ME) from different materials as silicon, glass, or polymers with part of all the necessary components of an immunoassay... 

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