CARBON NANOTUBES AS KNIVES FOR CUTTING VITREOUS ICE

该子项目是利用 由NIH/NCRR资助的中心赠款提供的资源。子项目和 研究者（PI）可能从另一个NIH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 中心，不一定是研究者的机构。 断层成像重建的冷冻水合生物样品，嵌入在无定形冰，是一个强大的方法，在其最初的天然条件下的细胞结构的研究。 然而，很少有生物样品沿束轴沿着小于0.5微米，薄到足以用300 KeV电子整体观察。 因此，重要的是开发用于在冷冻时切片细胞的方法。 一个好的冷冻超薄切片机中的金刚石刀可以切割所需的切片，而不需要将它们加热到无定形冰结晶的温度，但是稳定的金刚石刀很厚（刀刃处的角度为25-35度），所以无定形冰通常会被切割过程压缩和急剧弯曲。 为了解决这些问题，我们正在研究使用碳纳米管（CNT）作为设备，可以用作紧密的电线，从一块玻璃化的生物材料上切下薄片。 单壁碳纳米管的半径约为1纳米，小于锋利的金刚石刀边缘的曲率。 碳纳米管可以是毫米长，并且已知是坚固的，但相对于无定形冰的强度仍有待确定。 我们已经研究了商业上获得的和国产的碳纳米管在扫描电子显微镜，从他们的邻居通过显微操作解开。我们将它们拉伸到钨丝的细环上，并开发了一种“焊接”工艺，在CNT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CNT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，这样我们就可以了解我们计划的切片术的物理要求。

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.