Indentation quantification for in-liquid nanomechanical measurement of soft material using an atomic force microscope: rate-dependent elastic modulus of live cells.
Indentation quantification for in-liquid nanomechanical measurement of soft material using an atomic force microscope: rate-dependent elastic modulus of live cells.
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DOI：
10.1103/physreve.88.052711
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发表时间：
2013-11
期刊：
影响因子：
--
通讯作者：
Zou Q
中科院分区：
文献类型：
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作者：
Ren J;Yu S;Gao N;Zou Q
本文提出了一种基于控制的方法来取代传统的方法来实现精确的压痕定量，用于原子力显微镜下活细胞的纳米力学测量。准确的压痕定量是基于探针的纳米力学性能测量的核心。然而，传统的活细胞液体纳米力学测量方法由于没有考虑相对探针加速度和水动力的影响，无法准确量化压痕。因此，在测量纳米力学性能时，会产生明显的误差和不确定性。在本文中，提出了一种基于控制的方法，通过使用先进的控制技术跟踪活细胞和硬参考样本上相同的激励力分布，并通过这两种测量中悬臂基座位移的差异来量化压痕，从而解释这些不利影响。所提出的基于控制的方法不仅消除了相对探头加速度效应，无需校准相关参数，而且在力负载率较高时显著降低了水动力效应。我们进一步假设，通过使用所提出的基于控制的方法，可以可靠地量化不同应激条件下活的人上皮细胞的速率依赖弹性模量，以预测细胞膜的弹性演化，从而可用于预测细胞行为。通过实施该方法，在力加载率从0.1到100 Hz变化三个数量级时，HeLa细胞在应力过程前后的弹性模量被量化，其中施加的力和压痕的幅度分别为0.4-2 nN和250-450 nm。在应力过程之前和之后，HeLa细胞的弹性模量与加载速率呈明显的幂律关系。此外，由于应力过程，HeLa细胞的弹性模量大幅降低了2至5倍。因此，我们的测量结果表明，基于控制的方案在量化和表征活细胞应力过程中纳米力学性能的演变方面是有效的。
In this paper, a control-based approach to replace the conventional method to achieve accurate indentation quantification is proposed for nanomechanical measurement of live cells using atomic force microscope. Accurate indentation quantification is central to probe-based nanomechanical property measurement. The conventional method for in-liquid nanomechanical measurement of live cells, however, fails to accurately quantify the indentation as effects of the relative probe acceleration and the hydrodynamic force are not addressed. As a result, significant errors and uncertainties are induced in the nanomechanical properties measured. In this paper, a control-based approach is proposed to account for these adverse effects by tracking the same excitation force profile on both a live cell and a hard reference sample through the use of an advanced control technique, and by quantifying the indentation from the difference of the cantilever base displacement in these two measurements. The proposed control-based approach not only eliminates the relative probe acceleration effect with no need to calibrate the parameters involved, but it also reduces the hydrodynamic force effect significantly when the force load rate becomes high. We further hypothesize that, by using the proposed control-based approach, the rate-dependent elastic modulus of live human epithelial cells under different stress conditions can be reliably quantified to predict the elasticity evolution of cell membranes, and hence can be used to predict cellular behaviors. By implementing the proposed approach, the elastic modulus of HeLa cells before and after the stress process were quantified as the force load rate was changed over three orders of magnitude from 0.1 to 100 Hz, where the amplitude of the applied force and the indentation were at 0.4–2 nN and 250–450 nm, respectively. The measured elastic modulus of HeLa cells showed a clear power-law dependence on the load rate, both before and after the stress process. Moreover, the elastic modulus of HeLa cells was substantially reduced by two to five times due to the stress process. Thus, our measurements demonstrate that the control-based protocol is effective in quantifying and characterizing the evolution of nanomechanical properties during the stress process of live cells.