Coating of Threads with Fluorescent Curli Fibers for\npH Sensing

Threads\ncoated with bioresponsive materials hold promise for innovative\nwearable diagnostics. However, most thread coatings reported so far\ncannot be easily customized for different analytes and frequently\nincorporate non-biodegradable components. Most optically active thread\ncoatings rely on dyes, which often exhibit irreversible responses.\nIn this work, we propose a biosensing coating for threads using curli\nfibers. Curli fibers are self-assembling fibers of the protein CsgA\nthat can be genetically engineered to sense rapidly evolving diagnostic\ntargets. We first established a simple electrostatic-mediated absorption\nprotocol for coating anionic cotton threads with anionic curli fibers\nusing an intervening cationic chitosan layer. We applied this protocol\nto two types of pH-sensing curli fibers, displaying either fluorescent\npHuji or mCitrine proteins. This process ensures extensive curli coating\nover the entire thread surface using only water-based solvents. The\nresulting protein-coated threads are moderately hydrophobic, stretchable,\nand can monitor pH changes in real time through fluorescence. The\ncoatings are also stable and functional on the surface for over 25\ncycles of use, highlighting their potential for reusable practical\napplications. This straightforward and adaptable protocol can be extended\nto coat threads with diverse sensing and responsive capabilities for\nintelligent clothing.