Radmacher M, Fritz M, Hansma P K
Department of Physics, University of California, Santa Barbara 93106, USA.
Biophys J. 1995 Jul;69(1):264-70. doi: 10.1016/S0006-3495(95)79897-6.
We have imaged mica coated with thin gelatin films in water, propanol, and mixtures of these two liquids by atomic force microscopy (AFM). The elastic modulus (Young's modulus) can be tuned from 20 kPa to more than 0.1 GPa depending on the ratio of propanol to water. The resolution is best in pure propanol, on the order of 20 nm, and becomes worse for the softer samples. The degradation in resolution can be understood by considering the elastic indentation of the gelatin caused by the AFM tip. This indentation becomes larger and thus the contact area becomes larger the softer the sample is. Therefore this study may be used to estimate the resolution to be expected with an AFM on other soft samples, such as cells. Nondestructive imaging was possible only by imaging at forces < 1 nN. This was difficult to achieve in contact mode because of drift in the zero load deflection of the cantilever, supposedly caused by temperature drift, but straightforward in tapping mode.
我们通过原子力显微镜（AFM）对在水、丙醇以及这两种液体的混合物中涂有薄明胶膜的云母进行了成像。根据丙醇与水的比例，弹性模量（杨氏模量）可从20千帕调节至超过0.1吉帕。在纯丙醇中分辨率最佳，约为20纳米，而对于较软的样品分辨率会变差。通过考虑AFM探针引起的明胶弹性压痕，可以理解分辨率的下降。样品越软，这种压痕就越大，因此接触面积也越大。所以这项研究可用于估计使用AFM对其他软样品（如细胞）进行成像时预期的分辨率。仅在力小于1纳牛的情况下才能进行无损成像。在接触模式下，由于悬臂零负载挠度的漂移（推测是由温度漂移引起的），很难实现这一点，但在轻敲模式下则很直接。
