Reagentless Immunoelectrodes

A similar procedure was used for antidigoxin antibody assay. Digoxin-benzo crown ether conjugates, rather than cortisol were entrapped in the PVC membrane of the K+ sensitive electrode. The detection limit was in the range of a few g/ml. The sensor was regenerated by a brief ( 60 s) immersion in glycine-HCl buffer, pH 2.8. The membrane was stable for 1-2 weeks under conditions of routine use. 

A novel immunosensor type for low-molecular weight analytes has 

less specific potentiometric immunoprobes are based on the antigen-induced potential shift of chemically modified semiconductor electrodes (Fig. 125) (Yamamoto et al., 1983). The surface of a titanium dioxide electrode is covered by a BrCN-activated polymer membrane and inserted into an antibody-containing solution. The antibody binds covalently to the activated electrode surface. The antigen to be determined is added when the potential difference between the sensor and a reference electrode is stable. As a result of the immunological reaction a new 

Yamamoto et al. (1978) proposed the use of an antibody-coated titanium dioxide electrode to detect HCG in the urine of pregnant women. However, the measured potential of such sensors also depends on buffer composition, pH, and the ionic strength of the sample. Moreover, nonspecific adsorption of proteins at the transducer surface falsifies the measurement. This means that the accuracy of the analysis depends on the ratio of specific and nonspecific interactions. 

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. 

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