Assessing micromechanical properties of cells with atomic force microscopy: importance of the contact point
Assessing micromechanical properties of cells with atomic force microscopy: importance of the contact point
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DOI：
10.1007/s10237-006-0046-x
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发表时间：
2007-04-01
影响因子：
3.5
通讯作者：
Yin, F. C. -P.
中科院分区：
文献类型：
--
作者：
Crick, S. L.;Yin, F. C. -P.
机械性能可以通过原子力显微镜（AFM）的压痕力-深度曲线获得，该曲线是根据尖端挠度和悬臂位置之间的关系计算的，即挠度曲线。压痕深度是在接触后，刚性和软质材料在相同悬臂推进量的尖端挠度之间的差异。由于接触点不能从实验数据中明确地确定，因此在估计材料性能时存在一些不确定性。通过模拟，本研究探讨了与接触点识别对估计材料性能的影响有关的一些重要问题。利用典型的AFM悬臂梁刚度对线性材料进行了仿真，结果表明，软材料和极硬材料的挠度曲线接触后区域的某些部分可以分别用二次函数和线性函数来近似。基于这些发现，我们首先开发并验证了一种客观的、自动的方法来识别具有线性特性的材料的接触点。然后，我们评估错误识别接触点的影响，有和没有噪音。如果接触点缺失< 50nm，则小压痕的材料性能是错误的，但当压痕超过200nm时，误差逐渐减小，并获得正确的材料刚度估计。然而，如果遗漏了bbb100nm的接触点，则无法准确估计材料的真实性能。噪声增加了小压痕处材料性能的不确定性，但缺少接触点和噪声的综合影响主要是前者。尽管该算法是针对线性材料开发的，但它也适用于某些非线性材料，使其具有更广泛的适用性。
Mechanical properties are obtainable from atomic force microscopy (AFM) indentation force-depth curves, which are calculated from relationships between tip deflection and cantilever position, i.e. deflection curves. Indentation depth is the difference between tip deflections on a rigid and a soft material for the same amount of cantilever advancement, after contact is made. Since the contact point cannot be unequivocally identified from experimental data, there is some uncertainty in estimating material properties. Using simulations, this study examines some important issues related to the influence of contact point identification on estimated material properties. Simulations for linear materials using a typical stiffness for an AFM cantilever demonstrate that certain portions of the post-contact region of deflection curves for soft and very stiff materials can be approximated by quadratic and linear functions, respectively. Based on these findings, we first develop and verify an objective, automatic method to identify the contact point for materials with linear properties. We then assess the effect of misidentifying the contact point, with and without noise. If the contact point is missed by < 50nm, material properties for small indentations are erroneous but the error decreases asymptotically beyond 200nm of indentation and the correct estimate of material stiffness is obtained. If the contact point is missed by > 100nm, however, the true material properties cannot be estimated accurately. Noise adds to uncertainty in material properties at small indentations but the combined effect of missing the contact point and noise is dominated by the former. Even though the algorithm was developed for linear materials, it is also suitable for certain nonlinear materials making it more generally applicable.