Li Longhai, Zhang Xu, Wang Hongfei, Lang Qian, Chen Haitao, Liu Lian Qing
College of Engineering, Northeast Agricultural University, Harbin 150030, China.
State Key Laboratory of Robotics, Shenyang Institute of Automation, Chinese Academy of Sciences, Shenyang 110016, China.
Nanomaterials (Basel). 2019 Apr 6;9(4):561. doi: 10.3390/nano9040561.
Atomic force microscopy (AFM) can characterize nanomaterial elasticity. However, some one-dimensional nanomaterials, such as DNA, are too small to locate with an AFM tip because of thermal drift and the nonlinearity of piezoelectric actuators. In this study, we propose a novel approach to address the shortcomings of AFM and obtain the radial Young's modulus of a DNA duplex. The elastic properties are evaluated by combining physical calculations and measured experimental results. The initial elasticity of the DNA is first assumed; based on tapping-mode scanning images and tip⁻sample interaction force simulations, the calculated elastic modulus is extracted. By minimizing the error between the assumed and experimental values, the extracted elasticity is assigned as the actual modulus for the material. Furthermore, tapping-mode image scanning avoids the necessity of locating the probe exactly on the target sample. In addition to elasticity measurements, the deformation caused by the tapping force from the AFM tip is compensated and the original height of the DNA is calculated. The results show that the radial compressive Young's modulus of DNA is 125⁻150 MPa under a tapping force of 0.5⁻1.3 nN; its original height is 1.9 nm. This approach can be applied to the measurement of other nanomaterials.
原子力显微镜（AFM）能够对纳米材料的弹性进行表征。然而，一些一维纳米材料，如DNA，由于热漂移和压电致动器的非线性，尺寸太小以至于AFM探针难以定位。在本研究中，我们提出了一种新颖的方法来解决AFM的缺点，并获得DNA双链体的径向杨氏模量。通过结合物理计算和实测实验结果来评估弹性特性。首先假设DNA的初始弹性；基于轻敲模式扫描图像和针尖 - 样品相互作用力模拟，提取计算得到的弹性模量。通过最小化假设值与实验值之间的误差，将提取的弹性值指定为该材料的实际模量。此外，轻敲模式图像扫描避免了将探针精确地定位在目标样品上的必要性。除了弹性测量外，还补偿了AFM针尖的敲击力引起的变形，并计算出DNA的原始高度。结果表明，在0.5 - 1.3 nN的敲击力下，DNA的径向压缩杨氏模量为125 - 150 MPa；其原始高度为1.9 nm。这种方法可应用于其他纳米材料的测量。
