Antigen-antibody complex piezoelectric crystal

Piezoelectric transducers The formation of antigen—antibody complexes impHes an increase of mass as compared with the antigen or the antibody alone that is detected with piezoelectric devices, such as a quartz crystal balance or a cantilever. 

Photoswitchable antigen/antibody (substrate/ receptor) complexes 1. Reversible immunosensors 2. Patterning of surfaces with biomaterials using antigen/antibody-biomaterial conjugates (Design of biosensor arrays, biochips) 1. Immobilization of systems on electronic transducers (electrodes, piezoelectric crystals, FET) or the assembly of biomaterials on inert supports by non-covalent interactions (eg. glass, polymers)... 

Immunoassays using piezoelectric detectors coated with antigen or antibody had been devised as early as 1972 (Shons et al., 1972). The mass increase resulting from the immunological complex formation leads to a measurable change of the resonance frequency of the piezoelectric crystal. Effects of temperature and electronic noise can be eliminated by using a pair of crystals. Such sensors are only applicable in the dry state. 

The future use of coated piezoelectric devices as immunochemical sensors, even directly in the liquid phase, is very promising and could be considered a very competitive alternative to other types of immunoassay. Only this technique and that of surface plasmon resonance provide labelless methods for the direct study of antigen-antibody reactions, and their analytical possibilities. The devices can be easily automated or combined with flow injection systems, extending their capability of continuous and repeated assays. This raises an exciting possibility of using crystal arrays to assay for different analytes in complex samples with an on-line display of the results. 

FIG. 7.30 Electronic and optical transduction of the formation of antigen-antibody affinity complexes on transducers (A) Amperometric transduction at an electrode (R /K Is a redox label In the electrolyte solution). (B) Transduction by faradic Impedance spectrosco . (C) Microgravimetric quartz crystal microbalance (QCM) transduction in the presence of a piezoelectric quartz crystal. (D) Surface plasmon resonance transduction. 

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