Protein patterning on a glass substrate with a capillary force lithography process enhanced by surface treatment processes

Protein patterning on a glass surface was achieved with a capillary force lithography (CFL) process with a self-assembled monolayer surface treatment in this work. A polystyrene line and space pattern was fabricated on the glass substrate by using a polydimethylsiloxane (PDMS) stamp with a capillary force lithography process. With this approach, it is possible to avoid high pressure, UV exposure, and high temperature. The thin polystyrene residual layer on the glass surface was removed by CF₄/O₂ plasma etching to complete the polystyrene pattern, and an O₂ plasma process was applied to make the exposed glass surface hydrophilic. The oxidized polystyrene area was modified into a hydrophobic one by using vaporized toluene to reduce non-specific protein binding. A self-assembled monolayer (SAM), 3-aminopropyltriethoxysiloxane (3-APTES), was used to amine-functionalize glass surface. The protein patterning was achieved and verified by immobilizing fluorescent labeled protein, fluorescein isothiocyanate conjugate - bovine serum albumin (FITC-BSA), on the amine-functionalized microscale line and space pattern. Surface adsorption of protein and 3-APTES was confirmed by analyzing the nitrogen and the oxygen compositions with an X-ray photoelectron spectrometer. The nitrogen peak showed a stronger signal when a 3-APTES layer was formed, and the signal gets stronger with protein adsorption on the 3-APTES layer. As a result, chemical patterning was achieved in this work by using a capillary force lithography process and was verified by protein patterning.