Antigen-antibody coupling

Immunological sensors use immobilized immunoagents. An immobilized antigen is used to detect an antibody, or an immobilized antibody is used to detect an antigen. When an antibody interacts with an antigen, or vice versa, there is a variation in electric charge, mass or optical properties, which can be detected directly with a variety of transducers. 

---

Membrane-covered optochemical sensors (optodes) with O2 sensitive or pH sensitive fluorescence indicators (e.g. pyrene butyric acid or hydroxypyrene trisulfonic acid) have been coupled with different enzyme reactions, such as the conversion of glucose, lactate, ethanol, or xanthine, and with antigen-antibody couples (Opitz and Lubbers, 1987). 

Piezoelectric measurements use the appearance of an electrical polarization, or a variation in an existing polarization, in certain anisotropic dielectric materials, for example, quartz. This polarization appears when a force is applied in the appropriate direction. The piezoelectric effect is reversible because the material can deform or vibrate when an electric field is applied in the appropriate direction. Piezoelectric devices are used at their resonance frequencies for the determination of small variations in mass. These variations may result firom biological reactions that involve association or coupling, for example, enzyme-inhibitor associations or antigen-antibody coupling. 

Qian, R.L., Mhatre, R., and Krull, I.S., Characterization of antigen-antibody complexes by size-exclusion chromatography coupled with low-angle lightscattering photometry and viscometry, /. Chromatogr. A, 787, 101, 1997. 

Dyed particles also are commonly used in diagnostic lateral flow tests (like the common home pregnancy test), as the colors can be seen with the eye without the need for special detectors. In this type of assay, antibodies or antigens are coupled to the dyed particles and a sample solution applied to the test strip carries them along within a membrane. The particles then are captured at points in the membrane that represent either a control or a positive sample result. Large numbers of color particles docking at these points within the membrane create the visual lines associated with these disposable tests. 

Anderson, P.W., Pichichero, M.E., Stein, E.C., Porcelli, S., Betts, R.F., Connuck, D.M., Korones, D., Insel, R.A., Zahradnik, J.M., and Eby, R. (1989) Effect of oligosaccharide chain length, exposed terminal group, and hapten loading on the antibody response of human adults and infants to vaccines consisting of Haemophilus influenzae type b capsular antigen uniterminally coupled to the diphtheria protein CRMI97./. Immunol. 142, 2464-2468. 

Gray, G.R. (1978) Antibodies to carbohydrates Preparation of antigens by coupling carbohydrates to proteins by reductive amination with cyanoborohydride. In Methods in Enzymology, (V. Ginsburg, ed.), Vol. 50, pp. 155-160. Academic Press, New York. 

QDs recognized specific antigens/antibodies -DNA immobilization to QDs surfaces and possibility of hybrid assemblies [35] -Coupled to transferrin, QDs underwent receptor-mediated endocytosis in cultured HeLa cells... 

The second strategy uses combinations of different antibodies coupled to fluorochromes with distinct emission maxima (5,9). The most relevant fluoro-chromes for combined antigen detection are fluorescein isothiocyanate (FITC abs. max. 494 nm, emiss. max. 517 nm), rhodamine isothiocyanate (TRITC ... 

Nofetumomab is a mouse monoclonal antibody coupled to 99mTc that is used for diagnostic purposes to determine extent of disease and to stage patients with small cell lung cancer. It binds a 40-kD antigen found on many tumor cell types, but also on some normal cells. It is an accurate indicator of extent of disease in biopsy-confirmed small cell lung cancer except in those patients with brain or adrenal metastases. 

---