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Open AccessArticle

Morphological and Mechanical Characterization of DNA SAMs Combining Nanolithography with AFM and Optical Methods

1
Department of Physics, University of Genova, via Dodecaneso 33, 16146 Genova, Italy
2
OPTMATLAB, Department of Physics, University of Genova, via Dodecaneso 33, 16146 Genova, Italy
*
Authors to whom correspondence should be addressed.
Materials 2020, 13(13), 2888; https://doi.org/10.3390/ma13132888
Received: 24 May 2020 / Revised: 20 June 2020 / Accepted: 25 June 2020 / Published: 27 June 2020
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. View Full-Text
Keywords: AFM; Spectroscopic Ellipsometry; DNA; self-assembled monolayers; ionic strength; molecular absorption AFM; Spectroscopic Ellipsometry; DNA; self-assembled monolayers; ionic strength; molecular absorption
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MDPI and ACS Style

Pinto, G.; Canepa, P.; Canale, C.; Canepa, M.; Cavalleri, O. Morphological and Mechanical Characterization of DNA SAMs Combining Nanolithography with AFM and Optical Methods. Materials 2020, 13, 2888.

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