An epitope imprinted polymer with affinity for kininogen fragments prepared by metal coordination interaction for cancer biomarker analysis†
Development of synthetic antibodies for early-stage cancer diagnosis is a pursued goal in materials research. Molecular imprinting has shown advantages for this purpose, whereas preparation of molecularly imprinted polymer (MIP) for peptide/protein recognition is still a challenge. In the present study, a new MIP as an artificial antibody for biomarker analysis was synthesized by epitope and surface-confined imprinting approaches. The target peptides (K-1944 and K-2209) were the amino acids 440–456 and 438–456 fragments of high molecular weight kininogen that have sensitivity and specificity for the diagnosis of gastric, colorectal and liver cancers. For molecular imprinting, a heptapeptide, as an epitope for recognition, was selected as a template and immobilized on silica. Metal coordination between Cu(II) and template residues (His and Asp) was employed to create the binding sites. 4-Vinylpyridine was used as both the monomer and coordinating ligand. After imprinting polymerization and silica removal, spherical MIP (DQGHGHQ-MIP) with recognition ability was obtained successfully. The MIP could distinguish the template from one amino acid mismatched peptide. It also has surface-confined binding sites with good affinity for epitope-containing larger molecules. The MALDI-TOF analysis demonstrated that K-1944 and K-2209 could be selectively extracted from spiked human serum by the MIP. The solid phase extraction by DQGHGHQ-MIP coupled with HPLC was performed and 71–88% recoveries for K-1944 and K-2209 in spiked serum were obtained. The results demonstrated that DQGHGHQ-MIP could be used as an artificial antibody in the target peptide analysis with good extraction and sample clean-up performance.