CEA, LIST, Diamond Sensors Laboratory, F-91191 Gif-sur-Yvette, France.
Langmuir. 2011 Oct 4;27(19):12226-34. doi: 10.1021/la2013649. Epub 2011 Aug 30.
Resonant microcantilevers have demonstrated that they can play an important role in the detection of chemical and biological agents. Molecular interactions with target species on the mechanical microtransducers surface generally induce a change of the beam's bending stiffness, resulting in a shift of the resonance frequency. In most biochemical sensor applications, cantilevers must operate in liquid, even though damping deteriorates the vibrational performances of the transducers. Here we focus on diamond-based microcantilevers since their transducing properties surpass those of other materials. In fact, among a wide range of remarkable features, diamond possesses exceptional mechanical properties enabling the fabrication of cantilever beams with higher resonant frequencies and Q-factors than when made from other conventional materials. Therefore, they appear as one of the top-ranked materials for designing cantilevers operating in liquid media. In this study, we evaluate the resonator sensitivity performances of our diamond microcantilevers using grafted carboxylated alkyl chains as a tool to investigate the subtle changes of surface stiffness as induced by electrostatic interactions. Here, caproic acid was immobilized on the hydrogen-terminated surface of resonant polycrystalline diamond cantilevers using a novel one-step grafting technique that could be also adapted to several other functionalizations. By varying the pH of the solution one could tune the -COO(-)/-COOH ratio of carboxylic acid moieties immobilized on the surface, thus enabling fine variations of the surface stress. We were able to probe the cantilevers resonance frequency evolution and correlate it with the ratio of -COO(-)/-COOH terminations on the functionalized diamond surface and consequently the evolution of the electrostatic potential over the cantilever surface. The approach successfully enabled one to probe variations in cantilevers bending stiffness from several tens to hundreds of millinewtons/meter, thus opening the way for diamond microcantilevers to direct sensing applications in liquids. The evolution of the diamond surface chemistry was also investigated using X-ray photoelectron spectroscopy.
共振微悬臂梁已经证明，它们在化学和生物制剂的检测中可以发挥重要作用。分子与机械微传感器表面上的目标物种相互作用通常会导致梁弯曲刚度的变化，从而导致共振频率的移动。在大多数生化传感器应用中，悬臂梁必须在液体中运行，尽管阻尼会降低传感器的振动性能。在这里，我们专注于基于金刚石的微悬臂梁，因为它们的转换特性超过了其他材料。事实上，在广泛的显著特征中，金刚石具有特殊的机械性能，使得制造具有比其他常规材料更高的共振频率和 Q 因子的悬臂梁成为可能。因此，它们似乎是设计在液体介质中工作的悬臂梁的首选材料之一。在这项研究中，我们使用接枝羧基烷基链作为工具来评估我们的金刚石微悬臂梁的谐振器灵敏度性能，以研究由于静电相互作用而引起的表面刚度的细微变化。在这里，己酸通过一种新颖的一步接枝技术固定在氢终止的多晶金刚石谐振微悬臂梁表面上，该技术也可以适应其他几种功能化。通过改变溶液的 pH 值，可以调节固定在表面上的羧酸部分的-COO(-)/-COOH 比例，从而实现表面应力的精细变化。我们能够探测微悬臂梁共振频率的演变，并将其与功能化金刚石表面上的-COO(-)/-COOH 端基的比例相关联，从而可以探测微悬臂梁表面上的静电势的演变。该方法成功地探测了微悬臂梁弯曲刚度的几十到几百毫牛顿/米的变化，从而为金刚石微悬臂梁在液体中的直接传感应用开辟了道路。还使用 X 射线光电子能谱法研究了金刚石表面化学的演变。
