Silk fibroin–mediated aqueous functionalization of PTFE membranes for robust plasmonic sensing

Functionalizing chemically inert substrates remains challenging because conventional activation methods, such as oxygen plasma treatment or vacuum deposition, require costly equipment and harsh conditions that risk damaging structural integrity. Naturally occurring amphiphilic proteins offer a green alternative, leveraging their intrinsic ability to spontaneously adsorb onto diverse solid surfaces. Here, we report a simple and rapid strategy to functionalize polytetrafluoroethylene (PTFE) membranes using water-based regenerated silk fibroin (RSF) solutions derived from silkworm cocoons and applied through vacuum-assisted filtration. Amphiphilic RSF rapidly and conformally adsorbs along the native porous architecture within millisecond timescales, enabling selective modulation of surface energy while preserving pore morphology. Subsequent filtration of aqueous gold nanoparticle (Au NP) dispersions yields dense and homogeneous coatings (∼65% surface coverage) with excellent reproducibility across multiple membranes. The resulting Au NP–RSF@PTFE membranes operate as robust plasmonic sensing substrates, exhibiting high spectral uniformity (relative standard deviation ' 5%) and quantitative detection of 4-nitrophenol and thiram down to 10⁻⁷ M. This protein-mediated approach provides a scalable, sustainable, and broadly applicable route for converting chemically inert membranes into high-performance plasmonic and environmental sensing interfaces.