Development of Microplate Immunoenzyme Determination of Nonylphenol with Magnetic Sample Concentration

Nonylphenol is an aromatic organic compound that has an estrogen-like effect and has a negative effect on the human endocrine system. A method has been developed for the competitive determination of nonylphenol using magnetic particles, rabbit antiserum, nonylphenol conjugate with soybean trypsin inhibitor (STI) and biotin. The principle of the analysis is the formation of immune complexes on the surface of magnetite particles due to covalent immobilization of protein G through the oriented immobilization of polyclonal antibodies from rabbit serum during a competitive reaction between the free analyte (nonylphenol) and the bound one (as part of the nonylphenol-STI-biotin conjugate) for the binding sites of specific antibodies. The detection of formed immune complexes is proposed to be carried out using a streptavidin-polyperoxidase conjugate, which makes it possible to achieve a nine-fold gain in the level of the analytical signal. The developed ELISA using magnetite particles allows us to achieve a detection limit of nonylphenol at the level of 3.8 ng/ml, which is 14.5 times lower in comparison with the classical competitive ELISA (55 ng/ml). Based on the results of the experimental work, the optimized volume of the test sample was 500 μl, which makes it possible to concentrate low-contaminated samples by 17 times.