Protein-Polymer Block Copolymer Thin Films for Detection of Small Proteins in Biological Matrices via Size-Exclusion

While biosensors have been developed to allow sensitive detection of biomolecules, limit of detection (LOD) is often increased by several orders of magnitude in biological matrices due to nonspecific binding events from off-target molecules. Here, we demonstrate the self-assembly of protein-polymer conjugate thin films into lamellar structures containing alternating domains of proteins and polymer meshes that can exclude molecules based on particle size. By comparing the diffusion of two analytes, streptavidin (52.8 kDa) and monomeric streptavidin (15.6 kDa), it is found that the larger protein streptavidin experiences greater resistance to diffusion into the films and is largely excluded from the film structure. Furthermore, by decreasing the polymer molecular weight and therefore the spacing of the polymer nanodomains, the thin films can be tuned to enhance selectivity for smaller molecules. When compared against a traditional surface-immobilized protein biosensor, the conjugate films achieve a two order of magnitude reduction in LOD when detecting monomeric streptavidin, resulting from both the greater density of binding sites within the thin films as well as the size-based exclusion of larger proteins.