Molecular imprinting based on metal-ion mediated recognition: Electrosynthesis of artificial receptors for the selective detection of peptides

Abstract

We describe the electrosynthesis of a molecularly imprinted polymer (MIP) based on a metallo-porphyrin, namely Zn(II)− 5,10,15,20-tetrakis-(p-aminophenyl)-porphyrin (ZnTAPP), as a new artificial receptor for the recognition of carnosine (β-Ala--His), used as a model dipeptide. The MIP architecture has been selected with the aim to exploit metal-ion mediated recognition leveraging carnosine ability to chelate metal ions as Zn(II) through its histidine moiety. Metal ion coordination in imprinting procedures is beneficial as it combines the flexibility of noncovalent approach with the strength and specificity of covalent one representing an attractive hybrid imprinting strategy. MIP assembly was monitored by cyclic voltammetry and electrochemical impedance spectroscopy (EIS) both showing MIP deposition on the electrode as well as template removal. FT-IR analysis confirmed carnosine entrapment within the electrosynthesized Zn-porphyrin, further confirmed by XPS characterization which also demonstrated a significant metal removal from polymer film upon treatment with EDTA. Interestingly, no significant EIS response was monitored on the as-treated film, revealing no carnosine rebinding in the absence of metal ion. High response specificity has instead emerged by EIS measurements on MIP as well as a good time stability and a remarkable selectivity with little or no cross-reactivity with other peptides, including histidine-bearing ones and peptides with high structural similarity. Tests in lysates from human neuron-derived cells revealed sensor applicability in real samples analysis. This strategy allows to achieve excellent analytical performances with high versatility being possibly expandable to the detection of any histidine-bearing molecules as aminoacids, peptides and proteins, and also to any target molecule able to interact with Zn(II) ions.