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

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⁻ (K_sp=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 flow-system characterizations and the particle size effect are also described in this paper.