Surface optimization of PMMA via oxygen plasma and APTES for antibody immobilization

Polymethyl methacrylate (PMMA) chip-based biosensors have been widely used in bioanalysis due to their excellent optical transparency, biocompatibility, and ease of fabrication. However, the low surface reactivity and high non-specific adsorption of PMMA hinder efficient biomolecule immobilisation, which limits the analytical reproducibility and performance. In this study, we propose an optimised surface modification strategy to improve antibody immobilisation on PMMA substrates by systematically controlling oxygen plasma treatment and silanisation using 3-aminopropyltriethoxysilane (APTES). The surface morphology and hydrophilicity under various plasma conditions were characterised, and the effect of APTES concentration on antibody binding efficiency was quantitatively evaluated. The antibody immobilisation performance was evaluated based on the signal-to-noise ratio using a digital enzyme-linked immunosorbent assay device (Small Machines, Republic of Korea). Our results indicate that an APTES silanisation with 5% concentration, following 30 s oxygen plasma treatment at 50 W, yields the most functionally active surface for antibody immobilisation. This study presents a reliable surface engineering strategy for immobilising biomolecules on PMMA and provides a foundation for more reproducible and high-performance biosensor platforms.