Molecular imprinting is a technique used to synthesize polymers that display selective recognition for a given template molecule of interest. In this study, the role of hydrogel electrostatic charge density on the recognition properties of protein-imprinted hydrogels was explored. Using 3-methacrylamidopropyl trimethylammonium chloride (MAPTAC) as a positively charged monomer and 2-acrylamido-2-methylpropane sulfonic acid (AMPS) as a negatively charged monomer, a number of acrylamide-based polyelectrolyte hydrogels with varying positive and negative charge densities were prepared. The imprinted hydrogels were synthesized in the presence of the target molecule bovine hemoglobin (Bhb). The ability of the hydrogels to selectively recognize Bhb was examined using a competitive template molecule, cytochrome c. The Bhb imprinted gels exhibited template recognition properties that were dependent on both the monomer charge density and on whether the chosen monomer carried a positive or negative charge.

In addition to polyelectrolye hydrogels, polyampholyte hydrogels containing both positively and negatively charged monomers were also synthesized. The simultaneous presence of two oppositely charged monomers in the pre-polymerization mixture resulted in imprinted hydrogels with cavities that contain highly specific functional group orientation. The polyampholyte hydrogels exhibited decreased swelling when compared to their polyelectrolyte counterparts, due to the shielding of repulsive interactions between oppositely charge monomers. This decreased swelling resulted in greater template recognition, but lower selectivity, when compared to their polyelectrolyte counterparts.

In addition, we found that common agents used in template extraction may be responsible for the specific and selective binding properties exhibited by molecularly imprinted polymers in many published studies, and the effect of variations of the template extraction protocol on the MIP recognition properties were also studied in depth.