Site-specific immobilization of proteins on non-conventional substrates via solvent-free initiated chemical vapour deposition (iCVD) process

Currently, the development of protein chips faces new requirements of improved environmental stability, disposability, and cost-effectiveness for their wide applicability in our daily life. Here, we demonstrate a new protein detection platform on low-cost plastic and paper substrates. To achieve this platform, a highly selective thiol–ene photochemical reaction between vinyl functionality on the surface and cysteine-linked protein was utilized to immobilize the relevant proteins on the disposable substrates. First, the surface of the flexible substrates was modified with a vinyl-containing polymer, poly(2,4,6,8-tetravinyl-2,4,6,8-tetramethyl cyclotetrasiloxane) (pV4D4), via a solvent-free initiated chemical vapour deposition (iCVD) process. Next, on the vinyl functionalized surface, cysteine-linked proteins were covalently immobilized by a UV-assisted thiol–ene click reaction. The solvent-free characteristic of iCVD enabled us to directly pattern the functionality on the substrate via shadow mask patterning. On the patterned substrate, selective immobilization of the proteins was possible. With four model proteins, including two fluorescent proteins, single-chain variable fragment (scFv), and non-immunoglobulin protein scaffold (human kringle domain), we successfully demonstrated the immobilization of proteins on various substrates including polyethylene (PE) film and chromatography paper.