Magnetic nanospheres with a molecularly imprinted shell for the preconcentration of diethylstilbestrol

We report on the preparation of magnetic nanoparticles coated with a surface imprinted polymer for use in the preconcentration of diethylstilbestrol (DES). The magnetic molecularly imprinted nanoparticles (m-MINPs) were fabricated by first coating magnetite nanoparticles with a layer of Nafion which is polyanionic. Next, the resulting particles were coated with polydopamine (which is polycationic at near-neutral pH values) in the presence of DES as a template. The thickness of the coating containing the DES template is quite thin so that it can be removed within 18 h. The m-MINPs devoid of DES have a typical diameter of 500 nm and exhibit fast adsorption kinetics and sensitive magnetic response to a magnet. The m-MINPs can recognize DES with high specificity over many other estrogens (separation factor beta > 1.9) and were employed for the dispersive solid-phase extraction of DES which then was quantified by HPLC. The method was applied to determine DES in (spiked) milk powder samples. The recoveries ranged from 90.7 to 105.2 % (intra-day) and from 85.5 to 102.3 % (inter-day) at spiking levels of 10, 50, and 100 ng g(-1). The linear ranges were 3.5-1,000 ng g(-1) with the correlation coefficient of 0.9983. The detection limit was 0.99 ng g(-1) of milk powder. The m-MINPs are reusable. After 12 adsorption-elution cycles, the recovery was still higher than 80 %.