The amount of cross-linker influences affinity and selectivity of nanoMIPs prepared by solid phase polymerization synthesis

NanoMIPs obtained by solid phase polymerization synthesis have the cross-linker methylene-bis-acrylamide usually added at 2 mol% concentration, with very few exceptions. Here we studied the influence on the binding properties of rabbit IgG nanoMIPs of variable amounts of methylene-bis-acrylamide in the range between 0 (no cross-linker) and 50 mol% concentration. The binding parameters were determined by equilibrium binding experiments and the results show that the degree of cross-linking defines three distinct types of nanoMIPs: i) those with a low degree of cross-linking, including nanoMIPs without cross-linker (0-05 mol%), showing low binding affinity, high density of binding sites and low selectivity; ii) nanoMIPs with a medium degree of cross-linking (1-18 mol%), showing higher binding affinity, low density of binding sites and high selectivity; iii) nanoMIPs with a high degree of cross-linking (32-50 mol%), characterized by nanopolymer - ligand non-specific interactions, with low binding affinity, high density of binding sites, and no selectivity. In conclusion, the results are particularly relevant in the synthesis of high-affinity, high selectivity nanoMIPs as they demonstrate that a significant gain in affinity and selectivity could be achieved with pre-polymerization mixtures containing quantities of cross-linker up to 10-20 mol%, well higher than those normally used in this technique