Immuno-based assays

Based on these chemosensors, biosensors can be set up such as glucose or H2O2 sensors. In this case the appropriate biological compound (glucose oxidase or catalase) must be immobilized on the chemosensor. Different optical sensors are also used as transducer elements for the production of biosensors, especially of immuno-sensors. Here the affinity component is immobilized on the tip of the fiber and all available immuno-sensing assays can be performed using this transducer element. Since these sensors cannot be sterilized and used for on-line monitoring in a bioprocess we refer to other publications [25-27]. 

Like in RILAs, an advantage of fluorescence detection is the possibility of developing homogeneous FILAs using direct or indirect (competitive or displacement) approaches. The fluorescence polarization immunoassay (PFIA) and their homolog fluorescence polarization immuno-like assay (PFILA) are two of the most widely used procedures in homogeneous fluoroassays. Both are based on the principle that fluorescence polarization gives a direct measure of the bound/free ratio of the labeled analyte (tracer) without the need for their separation [23, 28]. 

The popularity of aptamer-based assays has risen over the last several years in proteomics (25). Typical aptamers are single-stranded nucleic acids that can recognize target molecules. The general basis is similar to immuno-based methods. These aptamers are found by screening large libraries of nucleic acid sequences. This technology has been applied to several proteome-level detections (26-29). 

As E. coli 0157 H7 is the most implicated STEC serotype in human cases, numerous immuno-based methods for the detection of this specific serotype have been documented. They include conventional Enzyme Linked Immuno Sorbent Assays (ELISA) in microplates, one-step immuno-detection systems, fully automated systems and various non enzymatic immunological based systems like Rapid Plate Latex Agglutination (RPLA), Immuno-Magnetic Separation (IMS) or immuno-chromatography (Table 3). 

Gupta, S., Indelicato, S.R., Jetwa, V., Kawabata, T., Kelley, M., Mire Sluis, A.R., Richards, S.M., Rup, B., Shores, E., Swanson, S.J., and Wakshull, E. (2007) Recommendations for the design, optimization, and qualification of cell based assays used for the detection of neutralizing antibody responses elicited to biological therapeutics. Journal of Immuno logical Methods, 321, 1 18. 

Martin, J. K., Galloway, T., Evans, A., Lonsdale, C., Valenta, E., and White, G. P., Immuno-metric assay for human chorionic gonadotropin (HCG) based on enhanced luminescence. Clin. Chem. (Winston-Salem, N.C.) 34, 1220 (abstr.) (1988). 

Li, Z., Ling, L., Liu, X., Laus, R., Delcayre, A. (2010). A flow cytometry-based immuno-titration assay for rapid and accurate titer determination of modified vaccinia Ankara virus vectors. Journal of Virological Methods, 169, 87—94. 

Shyu, R.H., Shyu, H.R, Liu, H.W., et al., 2002b. Colloidal gold-based immuno-chromatographic assay for detection of ricin. Toxicon 40, 255-258. 

Based on IgG-bearing beads, a chemiluminescent immuno-biochip has been also realized for the model detection of human IgG. Biotin-labeled antihuman IgG were used in a competitive assay, in conjunction with peroxidase labelled streptavidin59. In that case, the planar glassy carbon electrode served only as a support for the sensing layer since the light signal came from the biocatalytic activity of horseradish peroxidase. Free antigen could then be detected with a detection limit of 25 pg (108 molecules) and up to 15 ng. 

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