Immobilization of Gold Nanoparticles in Localized Surface Plasmon Polariton-Coupled Hot Spots via Photolytic Dimerization of Aromatic Amine Groups for SERS Detection in a Microfluidic Regime

Plasmon-assisted chemistry is an effective tool for triggering various chemical transformations that can be performed with high spatial precision. Plasmon-triggering efficiency is ensured by a high concentration of light energy near the plasmonic surface and the resulting enhancement of the local electric field (EF). The coupling of different plasmonic nanostructures by multimodal plasmonic hot spots can significantly enhance the EF, increasing plasmon-triggering efficiency. In this work, we demonstrate that the coupling between the traveled surface plasmon polariton (SPP) wave and the localized surface plasmon (LSP) resonance can be used to effectively realize plasmon-induced organic reactions, even in hot spots between SPP-and LSP-supported Au nanostructures. The periodically modulated surface of the gold grating was used as an SPP-active plasmonic support, with spherical Au nanoparticles (AuNPs) ensuring LSP excitation. To model the chemical transformation, we utilized the dimerization of amino groups (previously grafted to Au nanostructures) with azo bridges between the AuNPs and Au grating. The reaction was performed in a microfluidic regime and resulted in AuNP immobilization on the grating surface. Experiments and theoretical studies indicated that the azo-bridge formation and AuNP immobilization occurred only under illumination with the SPP wavelength and proceeded more effectively on the grating walls (particularly the inflection points), where the EF enhancement is greatest due to LSP-SPP coupling. Created structures were subsequently demonstrated as a promising substrate for the SERS-based detection in the microfluidic regime.

Automated summary

This paper presents a method for plasmon-induced organic reactions using the coupling enhancement between silver nanoparticles and gold gratings, which leads to highly efficient plasmon-triggered reactions.