Protein-Polymer Block Copolymer Thin Films for Highly Sensitive Detection of Small Proteins in Biological Fluids

In nearly all biosensors, sensitivity is greatly reduced for measurements conducted in biological matrices due to nonspecific binding from off-target molecules. One method to overcome this issue is to design a sensor that enables selective size-based uptake of proteins. Herein, a protein-polymer conjugate thin-film biosensor is fabricated that self-assembles into lamellae containing alternating domains of protein and polymer. Analyte is captured in protein regions while polymer domains restrict diffusion of large molecules. Device sensitivity and size-based exclusion properties are probed using two analytes: streptavidin (SA, 52.8 kDa) and monomeric streptavidin (mSA2, 15.6 kDa). Tuning domain spacing by adjusting polymer molecular weight allows the design of films that relatively freely uptake mSA2 and largely restrict SA diffusion. Furthermore, when detecting the smaller mSA2, no reduction in the limit of detection (LOD) is observed when transitioning from detection in the buffer to detection in biological fluids. As a result, LOD measured in fluid samples is reduced by 2 orders of magnitude compared to a traditional surface-immobilized protein monolayer.