Volume 4, Issue 1

Molecularly imprinted polymers (MIPs) are highly cross-linked polymers with high binding capacity and selectivity to the target molecules. MIPs become increasingly important because of the potential applications in drug delivery, purification and separation. In spite of the tremendous progress that has been made in the molecular imprinting field, many challenges remain to be addressed, especially in transforming the binding event into a detectable optical signal. The combination of photonic crystal and molecular imprinting technique is becoming a popular research idea. Compared to the conventional MIPs, the molecularly imprinted photonic crystal sensors (MIPCB) have the advantage of directly convert the molecule recognition process into optical signal. This review comprehensively summarizes various MIPCB, including the principle of molecular imprinted photonic crystal sensors, recent development, some challenges and effective strategies for MIPCB.

A real-time heparin monitor is required to optimize the dosage of heparin and its antidote, protamine sulfate, during extracorporeal circulation procedures. The gate effect of molecularly imprinted polymer (MIP) is a potential tool for the rapid and selective sensing of heparin. We here present a method to stabilize the measurement of heparin concentration in whole blood using an MIP-grafted electrode. An initiator of radical polymerization, the diethyldithiocarbamicbenzyl group, was introduced onto the surface of an indium-tin oxide (ITO) electrode. Heparin sodium, methacryloxethyltrimethoxysilane, and acrylamide were dissolved in water, and methylenebisacrylamide was dissolved in dimethylformamide. A mixture of the two solutions was introduced into the 50 μm gap between the surfaces of a quartz crystal plate and the treated ITO electrode. Ultraviolet light was irradiated onto the surface of the ITO to graft the copolymer of the monomers, then the ITO was washed with a 1 M sodium chloride aqueous solution to remove the heparin template and obtain the MIP-grafted electrode. Cyclic voltammetry was performed with the MIP-grafted electrode in physiological saline or bovine whole blood containing 0-8 units/ mL heparin and 5 mM ferrocyanide as a redox marker, and the relationship between the current intensity and the heparin concentration was analyzed. The current intensity decreased as the heparin concentration in either saline or whole blood increased, and the sensitivity of the electrode to heparin in blood was approximately 52% of its sensitivity to heparin in saline. The grafted-electrode was washed with a protease-containing detergent (Sterizyme® S, Maruishi Pharmaceutical) between measurements in blood. The heparin-sensitivity of the washed electrode in blood was 77% of that in saline. No sensitivity to chondroitin sulfate C was observed but sensitivity to low molecular weight heparin was demonstrated. We thus conclude that selective and stable sensing of heparin can be achieved using an electrode grafted with heparinimprinted polymer.

Molecularly imprinted polymer brush layers and gel layers with both a lectin (ConA) and an antibody-IgG as biomolecular ligands for a target protein were formed on surface plasmon resonance (SPR) sensor chips via surface-initiated atom transfer radical polymerization (SIATRP) without and with a crosslinker, respectively. While the IgG-imprinted brush layers chip had almost the same affinity constant for target IgG as the nonimprinted brush layer chip, the affinity constant of the IgG-imprinted gel layer chip was approximately twice than that of the nonimprinted gel layer chip. These indicate that chemical crosslinks are very important factor to create distinct molecular recognition sites by molecular imprinting. Thus, biomolecular imprinting that uses biomolecular ligands and crosslinkers enables us to design polymer layer chips with distinct molecular recognition sites with a strong affinity for a target biomolecule. The molecularly imprinted gel layers chips with lectin and antibody ligands are promising candidates for fabricating SPR sensor systems to monitor target biomolecules such as proteins.