pH-tunable plasmonic properties of Ag nanoparticle cores in block copolymer micelle arrays on Ag films

Abstract

Particle-on-film plasmonic systems provide interesting plasmonic properties, which can be easily tuned by controlling the particle–film gaps. However, there has been no study on the active control of gap distances and the resulting plasmonic properties in response to the external stimuli. In this study, we introduce a particle–film plasmonic system with the ability of active control of particle–film gap distances and thus the plasmonic properties based on pH-responsive block copolymer micelle–metal monolayer arrays on metal films. We synthesize pH-sensitive polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) spherical micelles that contain Ag nanoparticles in the micellar core. Then, we demonstrate that the pH-sensitive micelle monolayer films on Ag films modulate gap distances between the Ag nanoparticles (Ag NPs) within micelle cores and Ag films, leading to great changes in particle–film plasmon couplings (gap plasmons) that strongly influence the surface-enhanced Raman scattering (SERS) signal. The suggested plasmonic system with dynamic plasmonic properties will play a critical role in diverse applications such as chemical and biosensors, diagnostics, and smart optical devices.