Department of Chemistry, University of California, Berkeley, CA 94720.
Department of Chemical and Biomolecular Engineering, University of California, Berkeley, CA 94720.
Proc Natl Acad Sci U S A. 2021 Mar 9;118(10). doi: 10.1073/pnas.2017616118.
The motion of nanoparticles near surfaces is of fundamental importance in physics, biology, and chemistry. Liquid cell transmission electron microscopy (LCTEM) is a promising technique for studying motion of nanoparticles with high spatial resolution. Yet, the lack of understanding of how the electron beam of the microscope affects the particle motion has held back advancement in using LCTEM for in situ single nanoparticle and macromolecule tracking at interfaces. Here, we experimentally studied the motion of a model system of gold nanoparticles dispersed in water and moving adjacent to the silicon nitride membrane of a commercial LC in a broad range of electron beam dose rates. We find that the nanoparticles exhibit anomalous diffusive behavior modulated by the electron beam dose rate. We characterized the anomalous diffusion of nanoparticles in LCTEM using a convolutional deep neural-network model and canonical statistical tests. The results demonstrate that the nanoparticle motion is governed by fractional Brownian motion at low dose rates, resembling diffusion in a viscoelastic medium, and continuous-time random walk at high dose rates, resembling diffusion on an energy landscape with pinning sites. Both behaviors can be explained by the presence of silanol molecular species on the surface of the silicon nitride membrane and the ionic species in solution formed by radiolysis of water in presence of the electron beam.
纳米粒子在表面附近的运动在物理学、生物学和化学中具有重要意义。液体细胞透射电子显微镜（LCTEM）是一种很有前途的技术，可以用于研究具有高空间分辨率的纳米粒子的运动。然而，由于缺乏对电子束如何影响粒子运动的理解，阻碍了将 LCTEM 用于界面处的原位单纳米粒子和大分子跟踪的进展。在这里，我们通过实验研究了金纳米粒子在水中的模型系统的运动，该系统在商业 LC 的氮化硅膜附近移动，并在广泛的电子束剂量率范围内进行研究。我们发现纳米粒子表现出由电子束剂量率调制的异常扩散行为。我们使用卷积深度神经网络模型和正则统计测试对 LCTEM 中的纳米粒子异常扩散进行了表征。结果表明，在低剂量率下，纳米粒子的运动受分数布朗运动控制，类似于粘弹性介质中的扩散，在高剂量率下，类似于具有钉扎位的能量景观上的连续时间随机漫步，类似于扩散。这两种行为都可以用氮化硅膜表面上的硅醇分子种类和电子束存在下水中的辐射分解形成的溶液中的离子种类来解释。
