Dey Priyanka, Baumann Verena, Rodríguez-Fernández Jessica
Department of Physics and CeNS, Ludwig-Maximilians-Universität München, 80539 Munich, Germany.
Nanosystems Initiative Munich (NIM), 80799 Munich, Germany.
Nanomaterials (Basel). 2020 May 14;10(5):942. doi: 10.3390/nano10050942.
Plasmon-coupled colloidal nanoassemblies with carefully sculpted "hot-spots" and intense surface-enhanced Raman scattering (SERS) are in high demand as photostable and sensitive plasmonic nano-, bio-, and chemosensors. When maximizing SERS signals, it is particularly challenging to control the hot-spot density, precisely position the hot-spots to intensify the plasmon coupling, and introduce the SERS molecule in those intense hot-spots. Here, we investigated the importance of these factors in nanoassemblies made of a gold nanorod (AuNR) core and spherical nanoparticle (AuNP) satellites with ssDNA oligomer linkers. Hot-spot positioning at the NR tips was made possible by selectively burying the ssDNA in the lateral facets via controlled Ag overgrowth while retaining their hybridization and assembly potential at the tips. This strategy, with slight alterations, allowed us to form nanoassemblies that only contained satellites at the NR tips, i.e., directional anisotropic nanoassemblies; or satellites randomly positioned around the NR, i.e., nondirectional nanoassemblies. Directional nanoassemblies featured strong plasmon coupling as compared to nondirectional ones, as a result of strategically placing the hot-spots at the most intense electric field position of the AuNR, i.e., retaining the inherent plasmon anisotropy. Furthermore, as the dsDNA was located in these anisotropic hot-spots, this allowed for the tag-free detection down to 10 dsDNA and a dramatic SERS enhancement of 1.6 × 10 for the SERS tag SYBR gold, which specifically intercalates into the dsDNA. This dramatic SERS performance was made possible by manipulating the anisotropy of the nanoassemblies, which allowed us to emphasize the critical role of hot-spot positioning and SERS molecule positioning in nanoassemblies.
具有精心设计的“热点”和强烈表面增强拉曼散射(SERS)的等离子体耦合胶体纳米组装体,作为光稳定且灵敏的等离子体纳米、生物和化学传感器,有着很高的需求。在最大化SERS信号时,控制热点密度、精确地定位热点以增强等离子体耦合,以及在那些强烈热点中引入SERS分子,都极具挑战性。在此,我们研究了这些因素在由金纳米棒(AuNR)核心和带有单链DNA(ssDNA)低聚物连接体的球形纳米颗粒(AuNP)卫星构成的纳米组装体中的重要性。通过可控的银过度生长将ssDNA选择性地埋入侧面,同时保留其在尖端的杂交和组装潜力,从而实现热点在纳米棒尖端的定位。该策略稍作改动后,使我们能够形成仅在纳米棒尖端包含卫星的纳米组装体,即定向各向异性纳米组装体;或在纳米棒周围随机定位卫星的纳米组装体,即非定向纳米组装体。与非定向纳米组装体相比,定向纳米组装体具有更强的等离子体耦合,这是因为将热点战略性地置于金纳米棒最强电场位置,即保留了固有的等离子体各向异性。此外,由于双链DNA(dsDNA)位于这些各向异性热点中,这使得能够实现低至10个双链DNA的无标记检测,以及对特异性插入双链DNA的SERS标签SYBR gold的1.6×10的显著SERS增强。通过操控纳米组装体的各向异性实现了这种显著的SERS性能,这使我们能够强调热点定位和SERS分子定位在纳米组装体中的关键作用。