Is dielectrophoresis effective for increasing local concentration of particles in liquid-cell transmission electron microscopy?
Is dielectrophoresis effective for increasing local concentration of particles in liquid-cell transmission electron microscopy?
复制标题
介电泳对于增加液池透射电子显微镜中颗粒的局部浓度是否有效？
DOI：
10.1017/s1431927622007565
复制
发表时间：
2022
影响因子：
2.8
通讯作者：
Kimura Yuki
中科院分区：
文献类型：
--
作者：
Yamazaki Tomoya;Niinomi Hiromasa;Katsuno Hiroyasu;Hosseinkhannazer Hooman;Daigle Eric;Kimura Yuki
液池透射电子显微镜（LC-TEM）是一种通过将溶液样品夹在两个膜之间并将其引入TEM的真空室而不使其挥发来观察溶液样品的技术。该技术能够以足够的空间和时间分辨率从水溶液中捕获成核（结晶的初始过程），并提供了对该过程的深入了解[1，2]。然而，在技术上仍然难以捕获成核，因为在液池中控制过饱和（其是结晶的驱动力）是具有挑战性的。控制过饱和度的一种方法是使用辐解。辐解可以通过还原金属离子沉淀金属颗粒[3]或产生初始溶液中不存在的离子，并沉淀包含这些离子的晶体[4，5]。因此，辐解已被用于控制过饱和度，以驱动某些系统中的结晶。为了在更广泛的体系中控制过饱和度，有必要开发一种新的方法。在这里，我们专注于介电泳（DEP）[6]。DEP是当向电极施加电压时，溶液中的颗粒被电极周围产生的不均匀电场梯度移动的现象。通过对溶液中的颗粒充分施加DEP力，颗粒可以被收集在电极周围，这增加了颗粒的局部浓度，并且与过饱和度的控制直接相关。可以通过DEP收集的颗粒尺寸相对较大，例如蛋白质分子[7]。在涉及LC-TEM的研究中提到了DEP [8]，但在LC-TEM中尚未观察到与DEP相关的现象，例如颗粒收集。在这项研究中，我们应用DEP控制的局部浓度的颗粒在溶液中使用定制设计的硅芯片配备了氮化硅膜，电隔离结构，和电极的设计和制造的Norcada，并观察它通过光学显微镜和透射电镜调查DEP的有效性。胶体溶液被用来作为样品，调查DEP内的液体细胞。我们使用光学显微镜和TEM（JEM-2100 F）与场发射枪在200 kV的加速电压。我们使用外部液池保持器和LC-TEM保持器（Poseidon Select）进行光学显微镜观察。两个保持器都配备有用于使溶液流动并向液体池施加电信号的通道。我们使用了两种类型的硅芯片，其电极可用于支架（图1）。一种是用于电化学实验的商业产品，另一种是具有两个电极的芯片，其间隙为几微米（图2）。后者被制造以增加电极周围的电场梯度，并增加样品溶液中颗粒上的DEP力。通过函数发生器施加交流信号。
Liquid cell transmission electron microscopy (LC-TEM) is a technique for observing a solution sample by sandwiching it between two membranes and introducing it into the vacuum chamber of a TEM without volatilizing it. This technique has a capability to capture nucleation, which is the initial process of crystallization, from an aqueous solution with sufficient spatial and temporal resolution, and has provided insights into the process [1, 2]. However, it is still technically difficult to capture nucleation because control of supersaturation, which is the driving force for crystallization, in the liquid cell is challenging. One way to control the supersaturation is to use radiolysis. Radiolysis can precipitate metal particles by reducing metal ions [3] or produce ions that are not present in the initial solution, and to precipitate crystals involving those ions [4, 5]. Thus, radiolysis has been used to control supersaturation to drive crystallization in certain systems. In order to control supersaturation in a wider range of systems, it is necessary to develop a new method. Here, we focused on dielectrophoresis (DEP)[6]. DEP is the phenomenon in which particles in a solution are moved by the inhomogeneous electric field gradient created around an electrode when a voltage is applied to the electrode. By adequately applying DEP force to the particles in solution, the particles can be collected around the electrode, which increases the local concentration of particles and is directly linked to the control of supersaturation. The particles that can be collected by DEP are relatively large in size, such as protein molecules [7]. DEP has been mentioned in studies involving LC-TEM [8], but phenomena related to DEP, such as particle collection, have not been observed in LC-TEM. In this study, we applied DEP to control the local concentration of the particles in solution using a custom-designed silicon chip equipped with a silicon nitride membrane, electrical isolation structures, and electrodes design and manufactured by Norcada, and observed it by optical microscopy and TEM to investigate the effectiveness of DEP.Colloidal solutions were used as samples to investigate the DEP inside the liquid cell. We used optical microscopes and a TEM (JEM-2100F) with a field-emission gun at an acceleration voltage of 200 kV. We used an external liquid-cell holder for observation by optical microscopes and an LC-TEM holder (Poseidon Select). Both holders are equipped with channels for flowing solution and applying electric signals to the liquid cell. We used two types of silicon chips with electrodes that can be used in the holders (Fig. 1). One is a commercial product used for electrochemical experiments, and the other is a chip with two electrodes with a gap of a few microns (Fig. 2). The latter was fabricated to increase the electric field gradient around the electrodes and to increase the DEP force on the particles in the sample solution. An ac signal was applied by a function generator.