Surface Functionalization of Polypropylene Using Sulfhydrated Supercharged Green Fluorescent Proteins

Polypropylene (PP) is widely used in medical packaging and filtration applications for its stability, strength, and low cost. However, its inert and hydrophobic surface limits broader functionality, necessitating surface modification to enhance its properties, such as durability, environmental resistance, and biocompatibility. While traditional coating materials offer improvements, their nonrenewable origins and associated environmental concerns have prompted a growing interest in sustainable alternatives. As a sustainable alternative, protein-based coatings offer inherent biodegradability and tunable functionality. Here, we report a simple, one-step, activation-free method for surface modification of PP using sulfhydrated green fluorescent proteins (GFPs). The approach involves reacting highly cationic GFP with 2-iminothiolane (Traut’s reagent), which targets surface-exposed primary amines and enables the conversion of amino to sulfhydryl group. The modified protein spontaneously adhered to the PP surfaces, forming a stable coating. The influence of surface charge and primary amines on the coating efficiency was evaluated using GFP variants with differing ratios of basic to acidic residues. We also monitored the coating efficiency under a range of physicochemical conditions, including varying the pH, ionic strength, reducing agents, and metal ion chelators. Surface morphology and property were characterized by atomic force microscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, and contact angle measurements. Finally, the protein-coated surface was functionalized with citrate-capped gold nanoparticles, which catalyzed the reduction of p-nitrophenol to p-aminophenol. We anticipate that this protein-based strategy will offer a sustainable and versatile platform for functionalizing polypropylene using intrinsic protein chemistry with potential applications in catalysis.