Velasco Leslie, Islam Aniqa N, Kundu Koustav, Oi Aidan, Reinhard Björn M
Department of Chemistry and The Photonics Center, Boston University, Boston, MA 02459, USA.
Nanoscale. 2024 Jun 20;16(24):11696-11704. doi: 10.1039/d4nr01288g.
Plasmonic molecules are discrete assemblies of noble metal nanoparticles (NPs) that are of interest as transducers in optical nanosensors. So far, NPs with diameters of ∼40 nm have been the preferred building blocks for plasmonic molecules intended as optical single molecule sensors due to difficulties associated with detecting smaller NPs through elastic scattering in conventional darkfield microscopy. Here, we apply 405 nm, 445 nm two-color interferometric scattering (iSCAT) microscopy to characterize polyethylene glycol (PEG) tethered dimers of 10 nm and 20 nm Ag NPs and their monomers. Dimers of both NP sizes can be discerned from their respective monomers through changes in the average iSCAT contrast. In the case of 20 nm Ag NPs, dimer formation induces a change in the sign of the iSCAT contrast, providing a characteristic signal for detecting binding events. 20 nm Ag NP dimers with 0.4 kDa and 3.4 kDa polyethylene glycol (PEG) spacers show iSCAT contrast distributions with significantly different averages on both wavelength channels. The iSCAT contrast measured for individual PEG-tethered 10 nm or 20 nm NP dimers as a function of time shows contrast fluctuations indicative of a rich structural dynamics in the assembled plasmonic molecules, which provides an additional metric to discern dimers from monomers and paves the path to a new class of interferometric plasmon rulers.
等离激元分子是贵金属纳米颗粒（NPs）的离散聚集体，作为光学纳米传感器中的换能器受到关注。到目前为止，直径约40 nm的纳米颗粒一直是用作光学单分子传感器的等离激元分子的首选构建单元，因为在传统暗场显微镜中通过弹性散射检测较小的纳米颗粒存在困难。在这里，我们应用405 nm、445 nm双色干涉散射（iSCAT）显微镜来表征聚乙二醇（PEG）连接的10 nm和20 nm银纳米颗粒二聚体及其单体。两种尺寸的纳米颗粒二聚体都可以通过平均iSCAT对比度的变化与它们各自的单体区分开来。对于20 nm的银纳米颗粒，二聚体的形成会导致iSCAT对比度的符号发生变化，为检测结合事件提供了一个特征信号。具有0.4 kDa和3.4 kDa聚乙二醇（PEG）间隔物的20 nm银纳米颗粒二聚体在两个波长通道上显示出平均iSCAT对比度分布显著不同。作为时间函数测量的单个PEG连接的10 nm或20 nm纳米颗粒二聚体的iSCAT对比度显示出对比度波动，这表明组装的等离激元分子中存在丰富的结构动力学，这为区分二聚体和单体提供了一个额外的指标，并为一类新型干涉等离激元尺子铺平了道路。
