CARBON NANOTUBES AS KNIVES FOR CUTTING VITREOUS ICE

该子项目是利用该技术的众多研究子项目之一 资源由 NIH/NCRR 资助的中心拨款提供。子项目及 研究者 (PI) 可能已从 NIH 的另一个来源获得主要资金， 因此可以在其他 CRISP 条目中表示。列出的机构是 对于中心来说，它不一定是研究者的机构。 对嵌入无定形冰中的冷冻水合生物样品进行断层扫描重建是研究原始状态下细胞结构的有力方法。 然而，很少有生物样品沿光束轴的厚度小于 0.5 微米，薄到可以用 300 KeV 电子观察整个样品。 因此，开发冷冻细胞切片的方法非常重要。 良好的冷冻超薄切片机中的金刚石刀可以切割所需的切片，而无需将其加热到非晶冰会结晶的温度，但稳定的金刚石刀很厚（刀刃的夹角为25-35度），因此非晶冰通常会在切割过程中被压缩并急剧弯曲。 为了解决这些问题，我们正在研究使用碳纳米管（CNT）作为装置，将其用作紧线，从玻璃化生物材料块上切下薄片。 单壁碳纳米管的半径约为 1 nm，小于锋利的金刚石刀边缘的曲率。 碳纳米管可以长达数毫米，并且强度很高，但相对于无定形冰的强度仍有待确定。 我们在扫描电子显微镜中检查了商业获得的和自制的碳纳米管，通过显微操作将其与邻近的碳纳米管分开。我们将它们拉伸在细细的钨丝环上，并开发了一种“焊接”工艺，可在碳纳米管和钨之间形成牢固的结合。 我们正在努力简化这一过程，以便它可以用于制造有用的数量基于碳纳米管的切割设备。 我们还在试验可以测量玻璃冰的硬度和粘度的设备，以便我们能够了解我们计划的切片的物理要求。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Tomographic reconstruction of frozen-hydrated biological samples, embedded in amorphous ice, is a powerful method for the study of cell structure in its initially native condition. However, few biological samples are less than 0.5 micrometers along the beam axis, thin enough to be viewed in their entirety with 300 KeV electrons. It is therefore important to develop methods for slicing cells while they are frozen. A diamond knife in a good cryo-ultramicrotome can cut the desired sections without warming them to temperatures at which amorphous ice will crystallize, but stable diamond knives are thick (the angle included at the knife edge is 25-35 degrees), so the amorphous ice is usually compressed and sharply bent by the cutting process. To solve these problems we are investigating the use of carbon nanotubes (CNTs) as devices that could be used as tight wires to sever thin slices from a block of vitrified biological material. Single walled CNTs have a radius of about 1 nm, less then the curvature at the edge of a sharp diamond knife. CNTs can be millimeters long and are known to be strong, but how strong relative to amorphous ice remains to be determined. We have examined commercially obtained and homegrown CNTs in a scanning electron microscope, disentangled from their neighbors by micromanipulation. We stretch them over a thin loop of tungsten wire and have developed a "welding" process that forms a strong bond between the CNT and the tungsten. We are working to streamline this process so it can be used to make useful numbers of CNT-based cutting devices. We are also experimenting with devices that can measure the hardness and viscosity of vitreous ice, so we can understand the physical requirements for the microtomy we plan.