Advanced plasmon resonance through controllable block copolymer self-assembly

Simple light manipulation in plasmonic systems enables amplification of surface-enhanced Raman scattering (SERS). This study first proposes the fabrication of portable block copolymer (BCP)-based distributed Bragg reflector (DBR) films and their integration into a SERS substrate based on Au nanoparticles (AuNPs), as a novel solution to facilitate scanning of the SERS sensitivity as a function of working wavelength (λ_w). Using a lamella-forming polystyrene-b-poly(2-vinyl pyridine) (PS-b-P2VP) copolymer, a template of defect-free multilayer nanostructures was achieved via thermal annealing under a symmetric confinement. The crosslinking control and incorporation of lactic acid (LA) into the 2VP units produced highly asymmetric giant lamellar structures, which led to BCP-based DBR films with feasible tunability in the reflected wavelength from visible to near-infrared regions. An independently attachable feature of the BCP-based DBR films allowed an immediate modulation of λ_w for the designated SERS sensor. The SERS sensitivity was significantly enhanced (by approximately 99 times) at a specific λ_w = 522 nm, and the integrated sensor had a remarkably low limit of detection (0.2 ppm) for the pesticide, Thiram, on the surface of apples under field conditions. Owing to its exceptional sensitivity and ease of fabrication, the proposed DBR-integrated SERS sensor demonstrates practical potential for food safety, agriculture, and environmental monitoring.