Molecular imprinting-based fluorescent chemosensor for histamine using zinc(II)–protoporphyrin as a functional monomer Original Research Article

A commercially available reagent zinc(II)–protoporphyrin (ZnPP) is used as a novel fluorescent functional monomer to synthesize molecularly imprinted polymers (MIPs) for the selective recognition of histamine. ZnPP having a Lewis acid binding site Zn, binds with the imidazolyl group of histamine through coordination. Association constant (Kass) and the number of accessible sites (N) between the MIP and the template are found to be dependent upon the template concentration. By using Scatchard’s plot, the Kass and N are determined as 4500 l/mol and 180 μmol/g when the concentration of histamine is 0.1–1 mmol/l, but the two values are obtained, respectively, as 270 l/mol and 1100 μmol/g when the concentration is 4–10 mmol/l. The binding ability was also evaluated more accurately with a multi-binding model. Highly binding affinity is found for the ZnPP-based polymer than that only using methacrylic acid (MAA) as a functional monomer. Fluorescence intensity of the MIP decreased with histamine concentration but saturation behavior is observed when the histamine concentration is above 1 mmol/l, indicating that histamine no longer coordinated with ZnPP in the MIP and led to the low association constant at this condition.