RESUMEN

Controlling the thickness and uniformity of biomaterial films is crucial for their application in various fields including sensing and bioelectronics. In this work, we investigated film assemblies of an engineered repeat protein─specifically, the consensus tetratricopeptide repeat (CTPR) protein ─a system with unique robustness and tunability. We propose the use of microreflectance spectroscopy and apparent color inspection for the quick assessment of the thickness and uniformity of protein-based biomaterial films deposited on oxidized silicon substrates. Initially, we characterized the thickness of large, uniform, spin-coated protein films and compared the values obtained from microreflectance spectroscopy with those obtained from other typical methods, such as ellipsometry and atomic force microscopy. The excellent agreement between the results obtained from the different techniques validates the effectiveness of microreflectance as a fast, noninvasive, and affordable technique for determining the thickness of biomaterial films. Subsequently, we applied microreflectance spectroscopy to determine the thickness of drop-casted CTPR-based films prepared from small protein solution volumes, which present a smaller surface area and are less uniform compared to spin-coated samples. Additionally, we demonstrate the utility of apparent color inspection as a tool for assessing film uniformity. Finally, based on these results, we provide a calibration of film thickness as a function of the protein length and concentration for both spin-coated and drop-casted films, serving as a guide for the preparation of CTPR films with a specific thickness. Our results demonstrate the remarkable reproducibility of the CTPR film assembly, enabling the simple preparation of biomaterial films with precise thickness.

Asunto(s)

RESUMEN

Strain is a powerful tool for tuning the properties of two-dimensional materials. Here, we investigated the effects of large, uniform biaxial compressive strain on the superconducting phase transition of multilayered 2H-NbSe2 flakes. We observed a consistent decrease in the critical temperature of NbSe2 flakes induced by the large thermal compression of a polymeric substrate (>1.2%) at cryogenic temperatures. For thin flakes (∼10 nm thick), a strong modulation of the critical temperature up to 1.5 K is observed, which monotonically decreases with increasing flake thickness. The effects of biaxial compressive strain remain significant even for relatively thick samples up to 80 nm thick, indicating efficient transfer of strain not only from the substrate to the flakes but also across several van der Waals layers. This work demonstrates that compressive strain induced from substrate thermal deformation can effectively tune phase transitions at low temperatures in 2D materials.

RESUMEN

Many biological surfaces have hairs, known as trichomes in plants. Here, the wettability and macro- and micro-scale features of olive leaves are analyzed. The upper leaf side has few trichomes, while the lower side has a high trichome density. By combining different techniques including electron and atomic force microscopy, trichome surfaces are found to be chemically (hydrophilic-hydrophobic) heterogeneous at the nano-scale. Both olive leaf surfaces are wettable by water, having a high water contact angle hysteresis and great drop adhesion. The ultra-structural pattern observed for epidermal pavement cells differs from the reticulate cuticle structure of trichomes which shows that leaf surface areas may be substantially different despite being located nearby. Our study provides evidence for the nano-scale chemical heterogeneity of a trichome which may influence the functional properties of biological surfaces, such as water and solute permeability or water capture as discussed here for plants.

Asunto(s)

RESUMEN

Under ambient conditions, surfaces are rapidly modified and contaminated by absorbance of molecules and a variety of nanoparticles that drastically change their chemical and physical properties. The atomic force microscope tip-sample system can be considered a model system for investigating a variety of nanoscale phenomena. In the present work we use atomic force microscopy to directly image nanoscale contamination on surfaces, and to characterize this contamination by using multidimensional spectroscopy techniques. By acquisition of spectroscopy data as a function of tip-sample voltage and tip-sample distance, we are able to determine the contact potential, the Hamaker constant and the effective thickness of the dielectric layer within the tip-sample system. All these properties depend strongly on the contamination within the tip-sample system. We propose to access the state of contamination of real surfaces under ambient conditions using advanced atomic force microscopy techniques.

RESUMEN

The present work analyses how the tip-sample interaction signals critically determine the operation of an Atomic Force Microscope (AFM) set-up immersed in liquid. On heterogeneous samples, the conservative tip-sample interaction may vary significantly from point to point - in particular from attractive to repulsive - rendering correct feedback very challenging. Lipid membranes prepared on a mica substrate are analyzed as reference samples which are locally heterogeneous (material contrast). The AFM set-up is operated dynamically at low oscillation amplitude and all available experimental data signals - the normal force, as well as the amplitude and frequency - are recorded simultaneously. From the analysis of how the dissipation (oscillation amplitude) and the conservative interaction (normal force and resonance frequency) vary with the tip-sample distance we conclude that dissipation is the only appropriate feedback source for stable and correct topographic imaging. The normal force and phase then carry information about the sample composition ("chemical contrast"). Dynamic AFM allows imaging in a non-contact regime where essentially no forces are applied, rendering dynamic AFM a truly non-invasive technique.

RESUMEN

Chemical information can be obtained by using atomic force microscopy (AFM) and force spectroscopy (FS) with atomic or molecular resolution, even in liquid media. The aim of this paper is to demonstrate that single molecules of avidin and streptavidin anchored to a biotinylated bilayer can be differentiated by using AFM, even though AFM topographical images of the two proteins are remarkably alike. At physiological pH, the basic glycoprotein avidin is positively charged, whereas streptavidin is a neutral protein. This charge difference can be determined with AFM, which can probe electrostatic double-layer forces by using FS. The force curves, owing to the electrostatic interaction, show major differences when measured on top of each protein as well as on the lipid substrate. FS data show that the two proteins are negatively charged. Nevertheless, avidin and streptavidin can be clearly distinguished, thus demonstrating the sensitivity of AFM to detect small changes in the charge state of macromolecules.