Fraunhofer IAF , Institute for Applied Solid State Physics , Tullastraße 72 , 79108 Freiburg , Germany.
Anal Chem. 2019 May 7;91(9):5537-5541. doi: 10.1021/acs.analchem.9b00693. Epub 2019 Apr 18.
Diamond is a highly attractive coating material as it is characterized by a wide optical transparency window, a high thermal conductivity, and an extraordinary robustness due to its mechanical properties and its chemical inertness. In particular, the latter has aroused a great deal of interest for scanning probe microscopy applications in recent years. In this study, we present a novel method for the fabrication of atomic force microscopy (AFM) probes for force spectroscopy using robust diamond-coated spheres, i.e., colloidal particles. The so-called colloidal probe technique is commonly used to study interactions of single colloidal particles, e.g., on biological samples like living cells, or to measure mechanical properties like the Young's modulus. Under physiological measurement conditions, contamination of the particle often strongly limits the measurement time and often impedes reusability of the probe. Diamond as a chemically inert material allows treatment with harsh chemicals without degradation to refurbish the probe. Apart from that, the large surface area of spherical probes makes sensitive studies on surface interactions possible. This provides detailed insight into the interface of diamond with other materials and/or solvents. To fabricate such probes, silica microspheres were coated with a nanocrystalline diamond film and attached to tipless cantilevers. Measurements on soft polydimethylsiloxane (PDMS) show that the manufactured diamond spheres, even though possessing a rough surface, can be used to determine the Young's modulus from a Derjaguin-Muller-Toporov (DMT) fit. By means of force spectroscopy, they can readily probe force interactions of diamond with different substrate materials under varying conditions. The influence of the surface termination of the diamond was investigated concerning the interaction with flat diamond substrates in air. Additionally, measurements in solution, using varying salt concentrations, were carried out, which provide information on double-layer and van-der-Waals forces at the interface. The developed technique offers detailed insight into surface chemistry and physics of diamond with other materials concerning long and short-range force interactions and may provide a valuable probe for investigations under harsh conditions but also on biological samples, e.g., living cells, due to the robustness, chemical inertness, and biocompatibility of diamond.
钻石是一种极具吸引力的涂层材料，因为它具有宽的光学透明度窗口、高热导率以及由于其机械性能和化学惰性而具有的非凡坚固性。特别是后者近年来由于其在扫描探针显微镜应用中的潜力而引起了极大的兴趣。在这项研究中，我们提出了一种使用坚固的金刚石涂层球体（即胶体粒子）制造原子力显微镜（AFM）探针进行力谱学的新方法。所谓的胶体探针技术通常用于研究单个胶体粒子的相互作用，例如在生物样本（如活细胞）上，或用于测量机械性能，如杨氏模量。在生理测量条件下，粒子的污染常常强烈限制测量时间，并且常常阻碍探针的可重复使用。由于金刚石是一种化学惰性材料，因此可以用腐蚀性化学品进行处理而不会降解，从而可以对探针进行翻新。除此之外，球形探针的大表面积使得可以对表面相互作用进行敏感研究。这提供了对金刚石与其他材料和/或溶剂之间的界面的详细了解。为了制造这种探针，使用纳米晶金刚石薄膜对二氧化硅微球进行了涂层，并将其附着到无尖端悬臂梁上。对软质聚二甲基硅氧烷（PDMS）的测量表明，即使制造的金刚石球体具有粗糙的表面，也可以用于通过德加古因-米勒-托波洛夫（DMT）拟合来确定杨氏模量。通过力谱学，可以在不同条件下轻松探测金刚石与不同基底材料的力相互作用。研究了金刚石表面终止对在空气中与平坦金刚石基底相互作用的影响。此外，还进行了在溶液中的测量，使用了不同的盐浓度，这些测量提供了有关界面双层和范德华力的信息。所开发的技术提供了有关金刚石与其他材料的表面化学和物理的详细信息，涉及长程和短程力相互作用，并且由于金刚石的坚固性、化学惰性和生物相容性，它可能成为在恶劣条件下进行研究的有价值的探针，也可能成为生物样本（例如活细胞）的探针。
