Quartz crystal microbalance-based biosensing of proteins using molecularly imprinted polydopamine sensing films: Interplay between protein characteristics and molecular imprinting effect

Biomimetic sensing films based on molecularly imprinted polydopamine (MIPDA) offer a simple, biocompatible, and versatile approach to functionalise quartz crystal microbalance (QCM)-based biosensors for the recognition of target proteins. This study aims to investigate the chemical, morphological, and recognition properties of MIPDA sensing films polymerised on the QCM crystal surface, and to elucidate the impacts of various parameters on the liquid-phase biosensing behaviour. Pepsin, bovine serum albumin, human serum albumin, and lysozyme were used as model proteins to study the effect of molecular imprinting and the influence of protein characteristics on the recognition behaviour of MIPDA-functionalised QCM crystals. Analysis of the protein adsorption patterns revealed that the MIPDA film contained heterogeneous binding sites with a dissociation constant in the µM range, showing that the binding affinity of the synthetic sensing film for the target protein was comparable to that of commonly used bioreceptors. In a case study using a pepsin-imprinted MIPDA film, the specific conformation and surface chemistry of the recognition cavities were discovered to promote the binding of pepsin (imprinting factor = 5.78) while simultaneously reducing the nonspecific binding of incompatible proteins on the QCM crystal surface. Protein recognition on MIPDA-functionalised QCM crystals was found to be governed by a combination of nonspecific interactions (e.g., electrostatic and polar interactions) between the proteins and the MIPDA sensing film. The findings indicate that increasing the density of selective recognition cavities in the MIPDA film and optimising the sample pH are key strategies to improve the selectivity and sensitivity for protein biosensing.