Pinto Giulia, Canepa Paolo, Canale Claudio, Canepa Maurizio, Cavalleri Ornella
Department of Physics, University of Genova, via Dodecaneso 33, 16146 Genova, Italy.
OPTMATLAB, Department of Physics, University of Genova, via Dodecaneso 33, 16146 Genova, Italy.
Materials (Basel). 2020 Jun 27;13(13):2888. doi: 10.3390/ma13132888.
The morphological and mechanical properties of thiolated ssDNA films self-assembled at different ionic strength on flat gold surfaces have been investigated using Atomic Force Microscopy (AFM). AFM nanoshaving experiments, performed in hard tapping mode, allowed selectively removing molecules from micro-sized regions. To image the shaved areas, in addition to the soft contact mode, we explored the use of the Quantitative Imaging (QI) mode. QI is a less perturbative imaging mode that allows obtaining quantitative information on both sample topography and mechanical properties. AFM analysis showed that DNA SAMs assembled at high ionic strength are thicker and less deformable than films prepared at low ionic strength. In the case of thicker films, the difference between film and substrate Young's moduli could be assessed from the analysis of QI data. The AFM finding of thicker and denser films was confirmed by X-Ray Photoelectron Spectroscopy (XPS) and Spectroscopic Ellipsometry (SE) analysis. SE data allowed detecting the DNA UV absorption on dense monomolecular films. Moreover, feeding the SE analysis with the thickness data obtained by AFM, we could estimate the refractive index of dense DNA films.
利用原子力显微镜（AFM）研究了在不同离子强度下自组装在平整金表面的硫醇化单链DNA（ssDNA）薄膜的形态和力学性能。在硬轻敲模式下进行的AFM纳米刮削实验能够选择性地从微米级区域去除分子。为了对刮削区域成像，除了软接触模式外，我们还探索了定量成像（QI）模式的应用。QI是一种干扰较小的成像模式，能够获取有关样品形貌和力学性能的定量信息。AFM分析表明，在高离子强度下组装的DNA自组装单分子膜（SAMs）比在低离子强度下制备的薄膜更厚且更不易变形。对于较厚的薄膜，可以通过对QI数据的分析来评估薄膜与基底的杨氏模量之差。X射线光电子能谱（XPS）和光谱椭偏仪（SE）分析证实了AFM关于薄膜更厚且更致密的发现。SE数据能够检测致密单分子膜上DNA的紫外吸收。此外，将AFM获得的厚度数据输入到SE分析中，我们可以估算致密DNA薄膜的折射率。
