Colorimetric detection of morphine in a molecularly imprinted polymer using an aqueous mixture of Fe3+ and [Fe(CN)6]3-

In this work, a molecularly imprinted polymer (MIP) of morphine (MO) was prepared through thermal radical copolymerization of methacrylic acid (MAA) and ethylene glycol dimethacrylate (EDMA) in the presence of MO templates, and a molecularly imprinted sorbent assay (MIA) based on a colorimetric reporter was developed to determine the adsorption isotherm of MO–MIP binding. In practice, the MO-bound MIP was brought into contact with an aqueous mixture of Fe3+ and [Fe(CN)6]3- so that the 3-phenolic group of MO was oxidized and Fe3+ was reduced to Fe2+. As a result, the MO-bound MIP was stained with Prussian blue (PB), which was attributed to the instant co-precipitation of Fe2+ and [Fe(CN)6]3- (Ksp=10^-40). Accordingly, MO–MIP binding of the blue dye could be detected by visible spectroscopy. In addition, such staining could successfully distinguish MO from codeine. Upon data analyses, a two-site binding isotherm with two dissociation constants of 6.00×10^-5 and 1.03×10^-3 M was found for MO–MIP binding. MIAs for non-MIP were also performed. In addition, the results of flowsystem characterizations and the particle size effect are also described in this paper.