Novel Multidimensional Imaging of Surfaces with Atomic Force Microscopy

I. Sokolov
Tufts University,
United States

Keywords: atomic force microscopy, nanomechanics, multifrequency, dynamic mechanical spectroscopy, ringing mode, FT-NanoDMA


Atomic force microscopy (AFM) is a unique tool to visualize the physical and chemical properties of materials down to the nanoscale. It opens new dimensions in quantitative study and development of polymers, nanocomposites and biomaterials. AFM allows simultaneous collecting of multidimensional information of a sample surface. Here I overview recent developments of my lab in this direction. The 1st development is the fast Fourier-transfer nano-dynamical mechanical analysis/ spectroscopy (FT-NanoDMA) [1]. This nanoindentation mode allows to measure storage and loss moduli of soft materials at the range of biologically interesting small frequencies (up to 500Hz; the same range is used to describe polymers in industry). FT-NanoDMA is a combination of three different methods: the quantitative dynamic mechanical spectroscopy (DMS), AFM indentation, and Fourier-transform spectroscopy. This mode is fast and sensitive enough to allow DMS imaging of nanointerfaces and single biological cells. Compared to the existing state-of-the-art nanoindentation, FT-NanoDMA demonstrates ~ 100x improvements in both spatial (down to 10nm) and temporal resolution (down to 0.7 sec/pixel). I will show the work of this technique on known biomaterials, biological cells and polymers blends. The 2nd development is in the area of sub-resonant tapping, so-called Ringing mode [2, 3]. Compared to the existing sub-resonant tapping (such as Digital Pulse, PeakForce Tapping, HybriD, etc.), this mode allows obtaining to up to 8 new additional channels of information, such as adhesion height, adhesion neck height, detachment energy losses, size of possibly stretchable molecules, etc. In addition, Ringing mode can be up to 20 times faster and showing fewer artifacts compared to the existing sub-resonance tapping modes. I will demonstrate the work of this new mode on complex samples, such as fixed human epithelial cells, corneocyte skin flakes, and polymeric nanocomposites. Examples of potential medical applications of the presented modes will be overviewed [4]. References: 1. Dokukin, M. and I. Sokolov, High-resolution high-speed dynamic mechanical spectroscopy of cells and other soft materials with the help of atomic force microscopy. Scientific Reports, 2015. 5. 2. Sokolov, I. and M.E. Dokukin, Imaging of Soft and Biological Samples Using AFM Ringing Mode. Methods Mol Biol, 2018. 1814: p. 469-482. 3. Dokukin, M.E. and I. Sokolov, Nanoscale compositional mapping of cells, tissues, and polymers with Ringing mode of atomic force microscopy. Sci Rep, 2017. 7(1): p. 11828. 4. Sokolov, I., M.E. Dokukin, V. Kalaparthi, M. Miljkovic, A. Wang, J.D. Seigne, P. Grivas, and E. Demidenko, Noninvasive diagnostic imaging using machine-learning analysis of nanoresolution images of cell surfaces: Detection of bladder cancer. Proceedings of the National Academy of Sciences of the United States of America, 2018. 115(51): p. 12920-12925.