Mistras Group
Graphene Assists Researchers with Nondestructive Testing of Non-metallic Materials
Source: Proceedings of the National Academy of Sciences of the United States of America
The growing research in bioengineering calls for in vitro, non-invasive nanoscale characterization of biological macromolecules. However, current imaging tools often use ionizing radiation under high vacuum and/or cold temperature, conditions that are far from the native biological environment. We resolved this challenge by combining nano- Fourier transform infrared spectroscopy (nano-FTIR) with graphene-capped liquid cells that allow us to perform infrared spectroscopy of proteins in their natural liquid environment with nanometer spatial resolution. We monitored the dynamical assembly process and the nanoscale chemical structure of proteins under external stimuli by recording the amide I/II bands in the nano-FTIR absorption spectrum. Our platform opens opportunities for functional studies of soft materials, ranging from biomaterial (enzymes, virus) to polymer material, under in vitro conditions and external stimuli.


The nanoscale structure and dynamics of proteins on surfaces has been extensively studied using various imaging techniques, such as transmission electron microscopy and atomic force microscopy (AFM) in liquid environments. These powerful imaging techniques, however, can potentially damage or perturb delicate biological material and do not provide chemical information, which prevents a fundamental understanding of the dynamic processes underlying their evolution under physiological conditions. Here, we use a platform developed in our laboratory that enables acquisition of infrared (IR) spectroscopy and AFM images of biological material in physiological liquids with nanometer resolution in a cell closed by atomically thin graphene membranes transparent to IR photons. In this work, we studied the self-assembly process of S-layer proteins at the graphene-aqueous solution interface. The graphene acts also as the membrane separating the solution containing the proteins and Ca2+ ions from the AFM tip, thus eliminating sample damage and contamination effects. The formation of S-layer protein lattices and their structural evolution was monitored by AFM and by recording the amide I and II IR absorption bands, which reveal the noncovalent interaction between proteins and their response to the environment, including ionic strength and solvation. Our measurement platform opens unique opportunities to study biological material and soft materials in general.

Visit PNAS.org to view the paper.

Evident Ultrasonic Inspection Equipment