Enhanced selectivity of hydrogel-based molecularly imprinted polymers (HydroMIPs) following buffer conditioning

• Comparison of polyacrylamide, N-iso-propylacrylamide (NiPAm), and N-hydroxymethylacrylamide (NHMA) as hydrogel-based molecularly imprinted polymers (HydroMIPs).
• Selective recognition for a range of proteins: myoglobin (Mb), haemoglobin (Hb) and catalase (Cat).
• Improved selectivity through buffer preparation and conditioning.
• MIP/NIP selectivity ratios decreased depending on the buffer conditions in the order of Tris > PBS > succinate.
• Demonstration of MIP efficiency in real biological samples.

We have investigated the effect of buffer solution composition and pH during the preparation, washing and re-loading phases within a family of acrylamide-based molecularly imprinted polymers (MIPs) for bovine haemoglobin (BHb), equine myoglobin (EMb) and bovine catalyse (BCat). We investigated water, phosphate buffer saline (PBS), tris(hydroxymethyl)aminomethane (Tris) buffer and succinate buffer. Throughout the study MIP selectivity was highest for acrylamide, followed by N-hydroxymethylacrylamide, and then N-iso-propylacrylamide MIPs. The selectivity of the MIPs when compared with the NIPs decreased depending on the buffer conditions and pH in the order of Tris > PBS > succinate. The Tris buffer provided optimum imprinting conditions at 50 mM and pH 7.4, and MIP selectivities for the imprinting of BHb in polyacrylamide increased from an initial 8:1 to a 128:1 ratio. It was noted that the buffer conditions for the re-loading stage was important for determining MIP selectivity and the buffer conditions for the preparation stage was found to be less critical. We demonstrated that once MIPs are conditioned using Tris or PBS buffers (pH7.4) protein reloading in water should be avoided as negative effects on the MIP's imprinting capability results in low selectivities of 0.8:1. Furthermore, acidifying the pH of the buffer solution below pH 5.9 also has a negative impact on MIP selectivity especially for proteins with high isoelectric points. These buffer conditioning effects have also been successfully demonstrated in terms of MIP efficiency in real biological samples, namely plasma and serum.

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