Controlled Assembly of Gold Nanodiscs via DNA Hybridization: Tuning Plasmonic Coupling via Interparticle Gap Distance and Multimerization Degree

Metal nanoparticle assemblies induce interparticle plasmonic coupling, and precise control of this coupling by arranging the geometrical and spatial conditions is crucial for the application of plasmonic materials. In this study, gold nanodiscs (AuNDs) modified with complementary short DNA ligands (positive-sense DNA, (+)-DNA; negative-sense DNA, (-)-DNA) were assembled into 1D cylindrical structures with various interparticle gap distances and degrees of multimerization, enabling the precise tuning of plasmonic coupling strength. Specifically, AuNDs (90 nm in diameter) functionalized with 11-base (+)-DNA and (-)-DNA ligands were mixed and assembled into multimers through face-to-face interactions, driven by the hybridization of short DNA ligands without linker strands. This assembly induced strong plasmonic coupling owing to the short interparticle gap distance (5.7 nm), which led to significant peak shifts in the extinction spectra. Additionally, the plasmonic coupling strength was fine-tuned by varying the interparticle gap distance using DNA strands of different lengths (8, 11, and 20 base pairs). Furthermore, the assembly and disassembly temperatures of the DNA-AuNDs were tuned by adjusting (i) the salt concentration in the solution and (ii) the length of the DNA ligands. Finally, the degree of multimerization, which has a pronounced effect on the plasmonic coupling strength, was modulated by adjusting (i) the molar ratio of (+)-DNA-AuNDs to (-)-DNA-AuNDs and (ii) the salt concentration in the solution. This paper presents a simple and effective method to tune the plasmonic coupling of AuND assemblies, thereby expanding the potential applications of plasmonic materials.