Modern magnetic immunoassay: Biophysical and biochemical aspects

Abstract

In this review article an analysis of the biochemical and biophysical aspects of modern magnetic immunoassay (MIA) is conducted and additionally the problems and perspectives of its application in biology, biotechnology and medicine are defined. Magnetic immunoassay should be considered as an evolutionary extension of the classical immunoassay. MIA can have many variants of modifications, similar to the classic immunoenzymatic assay. The key distinctive element of the MIA is the use of magnetic particles (MPs), which are usually nanoparticles. MPs in the MIA can act as a marker for detection, or the solid phase at which the immunochemical reaction takes place. MIA possesses basic advantages over classical immunoassay methods: thanks to the unique magnetic properties of the MPs and the ability to manipulate it in the external magnetic field, it is possible to increase the informative value of the analysis (first of all, sensitivity and specificity), as well as the rigid requirements for “purity” of tested samples. For the purposes of immunoassay, magnetic particles of size from 10 to 200 nm are important, since such particles are in a superparamagnetic state, in the absence of strong magnetic fields; they are not agglomerated in a liquid medium. The size of the spherical particle determines the rate of sedimentation and mobility in the solution. The outer polymeric membrane serves as a matrix in which the surface functional groups are added, and also protects the core of the metal from the external environment. The outer shell may also consist of agarose, cellulose, porous glass, silicon dioxide etc. There are several strategies for the synthesis of nanoparticles: mechanical (dispersion), physical (gas phase deposition), wet chemical methods (chemical comprecipitation, thermal decomposition, methods of micro emulsion, hydrothermal reactions) and physico-chemical methods. Also used are magnesite nanoparticles of biogenic origin. Magnetic particles may function, and this is important for immunoassay. Surface functional groups include carboxylic, amino, epoxy, hydroxyl, tosyl, and N-hydroxysuccinate-activated groups. Magnetic spherical particles usually interact with surface molecules such as streptovidine, biotin, protein A, protein G, and immunoglobulin etc. Directions and prospects of the development of methods of magnetic immunoassay are determined, mainly, by the development of methods for detecting or influencing magnetic particles. In this case, the classical methods of detection are electrochemical methods, electrochemiluminescence, fluorescence. More modern ones include giant magnetoresistance, superconducting quantum interference devices, surface-enhanced Raman spectroscopy, biosensors based on nonlinear magnetization, magneto-PCR immunoassay. The current trend is to combine or integrate the application of various biochemical, physical, molecular and genetic, physico-chemical detection methods. In fact, all of these benefits undoubtedly open up broad prospects for the practical application of MIA in biology, biotechnology and medicine.