Spin-immunoassay

Forerunners of nonisotopic immunoassay had already appeared before radioimmunoassay was developed. For example, nephelometry is based on precipitation, which is known as the classical immune reaction, and the ideas of particle immunoassay and viroimmunoassay seem to have developed from the hemagglutination test. The principles of enzyme and fluorescence immunoassay had already been used as enzyme and fluorescence antibody techniques in histochemical analysis. In 1971, two groups reported use of an enzyme immunoassay (E5, V2). Leute et al. reported spin immunoassay, which has spurred recent development of nonisotopic immunoassays (L5). 

Spin immunoassay Free radicals Electron spin resonance... 

Spin immunoassay is also a type of homogeneous immunoassay. A change in the electron spin resonance (ESR) spectrum of a spin (marker)-labeled... 

Using spin labelled morphine it is possible to use ESR as an assay technique in this way for opium narcotics in urine and saliva, for antibodies derived from morphine are found to be also active against a number of related chemicals such as heroin and cocaine [164-166]. The absence of the possible hazards and inconveniences of radioactivity and the lack of a need to isolate the displaced molecules from those still bound to the antibody favour the spin immunoassay technique. The American army has been using this method of detection since 1972, and the measurement can be made in about 30 seconds. 

Leute RK, Ulhnan EF, Goldstein A, et al. Spin immunoassay technique for determination of morphine. Nature 1972 236 93-4. 

In this class of situations, all that is wanted is the amplitude of the signal. An example of this is spin-immunoassay [52], where the signal intensity is proportional to the amount of material under assay. The experimenter may be faced with the problem of obtaining the best possible signal-to-noise ratio without regard to lineshape distortions. The following is a check-list of options that can be considered. 

A review of the synthesis and chemistry of nitroxide spin labels includes a number of steroid derivatives. Novel spin-labelled steroids have been prepared by esterification with the nitroxyl carboxylic acid derivative (17),for use in spin immunoassays (SIA) as an alternative to radioactive labelling. The prednisolone ester (18), for example, exhibits an e.s.r. spectrum with narrow lines when it is in a free state in solution, but when bound to antibody the rate of tumbling is reduced, and linewidths are broad. Signals from bound and unbound derivatives are easily distinguished and measured, so SIA of antibody-bound prednisolone provides a potentially useful serum assay method. 

Fluorescein-labelled oestradiol has been used as a probe for anti-oestradiol antibody. The probe material was prepared by condensing the 6-carboxy-methyloximino-derivative of oestradiol with fluorescein amine . It had a fluorescence emission spectrum similar to that of fluorescein, and permitted a sensitive immunoassay of oestradiol. A system suitable for spin-immunoassay of steroids, using nitroxides for spin-labelling, is described on p. 264. 

Techniques for the detection or assay of various substances based on the reaction of those substances with specific antibodies (or vice versa, i.e. the detection and assay of antibodies using antigens). Such techniques include agglutination reactions, automated immune precipitation, complement fixation tests, crossed electrophoresis, counter electrophoresis, double diffusion, enzyme immunoassay, fluoroimmunoassay, haem-agglutination, immunoelectrophoresis, immunofluoresence, radial immunodiffusion, spin immunoassay, immunofixation, immunoradiometric assay and radioimmunoassay. See separate entries for these subjects. 

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