Poly(caffeic acid)-coated molecularly imprinted magnetic nanoparticles for specific and ultrasensitive detection of glycoprotein

Molecularly imprinted polymers (MIPs) are artificial chemical receptors, and can recognize template molecules with a high selectivity and affinity. As "antibody mimics", MIPs have been widely studied in various fields. However, the general applicability of MIPs is limited by the type of functional monomers. Herein, we developed caffeic acid (CA, a natural polyphenol) as novel a functional monomer. An innovative poly(caffeic acid)-coated molecularly imprinted magnetic nanoparticles (PCA-MIMN) with transferrin (TRF) as a model glycoprotein template was fabricated by autoxidation of CA with hexamethylenediamine (HMDA) in an aerobic environment as imprinted layer. The successful fabrication of PCA-MIMN was proved in detail by diversified characterization. The PCA-MIMN exhibited not only outstanding binding affinity and specificity for target glycoprotein, but also excellent hydrophilicity due to the externally generous hydrophilic groups. To evaluate the preeminent performance, the PCA-MIMN was linked with pH-triggered allochroic-graphene oxide (AGO), which was used for determination of TRF in real samples. The proposed PCA-MIMN linked AGO strategy exhibited ultrahigh sensitivity with limit of detection of 0.38 pg mL-1 for TRF. Finally, the proposed strategy was successfully applied in determination of TRF in spiked human serum sample with recovery and relative standard deviation in the range of 97.2%-103.9% and 4.6%-5.8%, respectively. This work demonstrates that the "autoxidation of CA with HMDA" may be a universal tool for synthesis of highly specific MIPs, and the type of functional monomers will increase exponentially due to the presence of numerous polyphenols in nature.