Stabilization of gold nanoparticles on glass surface with polydopamine thin film for reliable LSPR sensing

Localized surface plasmon resonance (LSPR) arising on noble metal plasmonic nanostructures has demonstrated compelling applications for label-free and in situ biosensing. A widely-used format for LSPR biosensing is to adsorb pre-synthesized plasmonic colloids on transparent substrates and track their surface plasmon band wavelength and/or intensity changes upon biomolecular binding or dissociation. However, this format suffers from the optical instability of the supported plasmonic colloids, which mainly originates from the detachment and/or aggregation of the supported colloids. In this work we report a novel strategy to stabilize the supported plasmonic colloids, with gold nanoparticles (AuNPs) as a model, on amine-functionalized glass for reliable plasmonic biosensing. In this strategy, polydopamine (PDA), a mussel-inspired polymeric thin film was explored to coat the AuNPs-attached glass by using a simple immersion reaction. The PDA thin film not only prevents the supported AuNPs from detaching or aggregating, but also allows for facile immobilization of biological probes for further plasmonic biosensing. Meanwhile, the refractive index (RI)-sensitivity of the coated AuNPs was essentially preserved by optimizing the thickness of the thin film, thus offering a reliable platform for LSPR sensing.