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Three-dimensional molecular resolution mapping of soft matter-liquid interfaces

Final Report Summary - 3DNANOMECH (Three-dimensional molecular resolution mapping of soft matter-liquid interfaces)

In 3DNanoMech we have developed several force microscopy-based tools and methods
to characterize with high-spatial resolution soft matter-liquid interfaces. The project has addressed problems of different spatial scales ranging from ions to cells.

We have designed a force microscope (3D-AFM) to imaging solid-liquid interfaces with atomic-resolution in the three spatial axes. The microscope has been applied to address several problems such as the organization common salt solutions near a mica surface or the interaction of liquid water with 2D materials surfaces.
The atomic-resolution capabilities of the 3D-AFM have enabled two relevant discoveries. At high molarities (4 M), common alkali halide salt solutions such as potassium chloride form an ordered interface of a few nanometers in thickness. This interface has both solid and liquid-like properties.
We have also discovered that water molecules are expelled from the vicinity of a 2D materials surface. The water is replaced by hydrophobic layers composed of gas and/or airborne molecules dissolved in the water. The data suggest that the formation of molecular-size hydrophobic layers is a universal property that applies to any extended hydrophobic surface immersed in liquid water.

We have developed a bimodal AFM configuration (AM-FM) to image with angstrom-spatial resolution the mechanical properties of surfaces immersed in a liquid. The method combines fast imaging, high-spatial resolution (atomic, molecular or nanoscale depending on the sample), quantitative and non-destructive mapping of several material properties such as the Young’s modulus, the loss modulus or the retardation time. The method enables to determine the Young’s modulus over a five orders of magnitude range (1 MPa to 100 GPa). This range includes a large variety of materials from single proteins to metal−organic frameworks.

We have developed a force microscopy method to generate subsurface maps of eukaryotic cells immersed in a cell culture medium. The method enables imaging of the nucleoli inside the nucleus, this is, organelles that lie 1-4 μm from the cell’s outer surface. At the same time, it provides high- resolution maps (~50 nm) of the actin cytoskeleton structure near the plasma membrane. The method combines an experimental approach with a theory that enables the transformation of forces into the cell nanomechanical properties. Nanomechanical maps have been applied to characterize the mechanical properties of cardiomyocytes, adipose cells and tissues.

In short, we have developed several high-resolution and quantitative force microscope methods to characterize soft matter-liquid interfaces for a variety of materials from single proteins to cells; from 2D materials to metal-organic-frameworks. The atomic-resolution capabilities of the 3D-AFM have enabled discovering two new types of solid-liquid interfaces. Subsurface imaging of cells has been achieved by exploiting nanomechanical interactions. This method opens a label-free approach to understand the relationship between the cell’s mechanical state and its physiology.