Asgari Nasrin, Baaske Martin Dieter, Ton Jacco, Orrit Michel
Huygens-Kamerlingh Onnes Laboratory, Leiden University, Postbus 9504, 2300 RA Leiden, The Netherlands.
Max Planck Institute of Biophysics, Max-von-Laue-Str. 3, 60438 Frankfurt am Main, Germany.
ACS Photonics. 2024 Feb 6;11(2):634-641. doi: 10.1021/acsphotonics.3c01482. eCollection 2024 Feb 21.
Measuring the orientation dynamics of nanoparticles and nonfluorescent molecules in real time with optical methods is still a challenge in nanoscience and biochemistry. Here, we examine optoplasmonic sensing taking the rotational diffusion of plasmonic nanorods as an experimental model. Our detection method is based on monitoring the dark-field scattering of a relatively large sensor gold nanorod (GNR) (40 nm in diameter and 112 nm in length) as smaller plasmonic nanorods cross its near field. We observe the rotational motion of single small gold nanorods (three samples with about 5 nm in diameter and 15.5, 19.1, and 24.6 nm in length) in real time with a time resolution around 50 ns. Plasmonic coupling enhances the signal of the diffusing gold nanorods, which are 1 order of magnitude smaller in volume (about 300 nm) than those used in our previous rotational diffusion experiments. We find a better angular sensitivity with plasmonic coupling in comparison to the free diffusion in the confocal volume. Yet, the angle sensitivity we find with plasmonic coupling is reduced compared to the sensitivity expected from simulations at fixed positions due to the simultaneous translational and rotational diffusion of the small nanorods. To get a reliable plasmonic sensor with the full angular sensitivity, it will be necessary to construct a plasmonic assembly with positions and orientations nearly fixed around the optimum geometry.
利用光学方法实时测量纳米颗粒和非荧光分子的取向动力学在纳米科学和生物化学领域仍然是一项挑战。在此，我们以等离子体纳米棒的旋转扩散作为实验模型来研究光等离子体传感。我们的检测方法基于监测一个相对较大的传感金纳米棒（GNR）（直径40 nm，长度112 nm）在较小的等离子体纳米棒穿过其近场时的暗场散射。我们以约50 ns的时间分辨率实时观察单个小金纳米棒（三个样品，直径约5 nm，长度分别为15.5、19.1和24.6 nm）的旋转运动。等离子体耦合增强了扩散金纳米棒的信号，这些金纳米棒的体积（约300 nm）比我们之前的旋转扩散实验中使用的金纳米棒小1个数量级。与共焦体积中的自由扩散相比，我们发现等离子体耦合具有更好的角度灵敏度。然而，由于小纳米棒同时存在平动和转动扩散，我们通过等离子体耦合发现的角度灵敏度与固定位置模拟预期的灵敏度相比有所降低。为了获得具有全角度灵敏度的可靠等离子体传感器，有必要构建一个等离子体组件，其位置和取向在最佳几何结构周围几乎固定。
