Local force titration of wood surfaces by chemical force microscopy

Chemical force microcopy, a variation of atomic force microscopy, opened the door to visualize chemical nano-properties of various materials in their natural state. The key function of this method is given by translating adhesion forces between a functionalized tip and the sample to chemical surface behavior. In force titration, these adhesion forces are studied in different pH buffers, which allows estimating the pKa value of the analyzed surface. Herein, we report the use of this method to study natural and chemically treated wood surfaces, which are of interest in sustainable material design. First, we show varying adhesion phenomena of OH- and COOH-functionalized tips on native spruce wood cells. Then, we demonstrate how peak force tapping with chemically functionalized tips can be used to estimate the pKa value of gold substrates (pKa ≈ 5.2) and different wood cell wall layers with high spatial resolution. Additionally, the swelling behavior of wood samples is analyzed in varying pH buffers. With the applied method, chemical surface properties of complex natural substrates can be analyzed. Graphical abstract

Chemical templates that assemble the metal superhydrides

The recent incessant discoveries of high-pressure hydrides totally altered our road map toward finding room temperature superconductors. Especially, metal superhydrides consisting of hydrogen covalent networks that resemble metallic hydrogen are favorable candidates for improving Tc and lowering pressure. However, the chemical force that drives the dissociation of H2 and the formation of H covalent network in superhydrides is unknown. Our high-throughput calculations show that, after removing H atoms, the remaining metal lattices exhibit unusual electron occupations at the interstitial regions, which matches excellently to the H lattice like a template. Furthermore, H lattices consist of 3D aromatic building units that are greatly stabilized by chemical templates of metals close to s-d boarder. The theory can help predicting ternary superhydrides that may form at lower pressure.

Single-particle chemical force microscopy to characterize virus surface chemistry

Two important viral surface characteristics are the hydrophobicity and surface charge, which determine the viral colloidal behavior and mobility. Chemical force microscopy allows the detection of viral surface chemistry in liquid samples with small amounts of virus sample. This single-particle method requires the functionalization of an atomic force microscope (AFM) probe and covalent bonding of viruses to a surface. A hydrophobic methyl-modified AFM probe was used to study the viral surface hydrophobicity, and an AFM probe terminated with either negatively charged carboxyl acid or positively charged quaternary amine was used to study the viral surface charge. With an understanding of viral surface properties, the way in which viruses interact with the environment can be better predicted.

Fast chemical force microscopy demonstrates that glycopeptidolipids define nanodomains of varying hydrophobicity on mycobacteria

We use chemical force microscopy with high spatiotemporal resolution to study the nanoscale distribution of hydrophobicity on living mycobacterial cells.

Visualization of the Stimuli-responsive Surface Behavior of Functionalized Wood Material by Chemical Force Microscopy

The hierarchical and porous wood structure provides a stable scaffold to design functionalized lignocellulosic materials with extended properties by chemical modification techniques. However, proper nanoscale characterization methods for these novel materials are needed to confirm the presence of the added functionality and to locate the introduced functional groups with high spatial resolution. Chemical force microscopy is a suitable characterization method to distinguish chemical surface characteristics by scanning the samples surface with a functionalized tip. We report the application of this nanotechnology method on both, unmodified and functionalized wood samples to confirm the thermo-responsive behavior of poly(N-isopropylacrylamide) (PNIPAM) modified spruce wood. By performing force measurements on ultra-microtomed surfaces, adhesion force differences on the analysed structure are monitored and reveal the location and functionality of introduced functional groups. The modified samples are scanned below and above their lower critical solution temperature with a hydrophobic tip in aqueous media to observe adhesion changes. Additionally, confocal Raman microscopy support the chemical force microscopy measurements by revealing the success of the modification and the distribution of PNIPAM across the sample cross-sections. The results show that PNIPAM is mainly located in wood cell wall areas close to the lumen in early- and transitionwood.