NanoIR Spectroscopy Journal Club

Determination of Polypeptide Conformation with Nanoscale Resolution in Water

by Georg Ramer, Francesco Simone Ruggeri, Aviad Levin, Tuomas P.J. Knowles, and Andrea Centrone

Key Points

  • Characterized the chemical composition and structure of heterogeneous protein aggregates in air and water down to the single aggregate (i.e., fibril) level;
  • Found that it is possible to acquire nanoscale infrared spectra in water/aqueous samples with a high signal-to-noise ratio (SNR) using photothermal-induced resonance; and
  • Achieved nanoscale resolved IR spectra and maps in air and water with comparable SNR and lateral resolution, overcoming the spatial resolution and sensitivity limitations of conventional spectroscopic methods.



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ACS Nano 2018, 12, 7, 6612–6619
DOI: 10.1021/acsnano.8b01425

Proteins are central to essentially all molecular processes in living organisms, typically carrying out their activities by folding into well-defined three-dimensional structures and by binding to other molecular species to form functional complexes. Infrared (IR) spectroscopy is well established as an important measurement capability for chemically characterizing the secondary structure of proteins both in solution and in the solid state. New nanoscale chemical characterization capabilities, such as photothermal AFM-IR spectroscopy, have enabled the determination of polypeptide conformations in a single protein fibrils and other submicron-sized protein structures, resulting in an improved understanding of such important processes as protein misfolding and aggregation mechanisms.

Until now, however, AFM-IR could only be performed on dried materials, and there is always a concern that the drying out of a protein-containing material may result in a conformational change in the protein backbone structure. The new approach and results described in this paper show that it is now possible to generate nanoscale resolved IR spectra and maps in air and water with comparable signal-to-noise ratio (SNR) and lateral resolution.


AFM-IR (PTIR), Infrared nanospectroscopy, Infrared spectrophotometry instrumentation, Protein aggregation, Protein structure