This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Very small biological samples and even individual biomolecules can now be examined under near-physiological conditions with high confidence at the BESSY II infrared beamline using a newly validated and improved technique: nanoscale infrared (IR) spectroscopy (s-SNOM) with ultrathin silicon-based membranes. An international team demonstrated, following an initial proof of concept, that high-resolution nano-IR measurements reliably match expected far-field IR spectra in an aqueous environment at a resolution of a few tens of nanometers.
This methodological advance provides a solid foundation for studying biomaterials or observing catalytic processes in a liquid environment. The work is published in the journal Analytical Chemistry. Infrared spectroscopy can provide insights into the properties of biological samples, molecules and soft matter.
However, the analysis requires a certain sample size, meaning that only statistical conclusions can be drawn about individual molecules. To investigate individual biomolecules, nanoscale spectroscopy (s-SNOM) using infrared light is ideal. In this technique, an infrared beam illuminates the tip of an atomic force microscope (AFM) as it scans the sample; the backscattered light provides local optical information about the near-field interaction between the tip and the sample, with a resolution of up to 10 nanometers.
Biomolecules naturally exist in aqueous environments, making s-SNOM analysis challenging because of water's strong infrared absorption. Initial proof-of-concept studies showed that in-liquid s-SNOM is achievable using ultrathin silicon nitride or silicon carbide membranes between the AFM tip and the sample. These membranes act as a protective film and are transparent to the mid-infrared range.
However, a comprehensive benchmark linking these local near-field measurements to established far-field IR reference spectra was lacking. To address this gap, an international team led by Dr. Alexander Veber performed a systematic study using ultrathin silicon-based membranes.
By thoroughly analyzing the influence of different membrane materials and the liquid environment, the researchers demonstrated that high-resolution nano-IR spectra acquired in aqueous environments directly correlate with standard far-field IR signatures. "We systematically tested various silicon membranes and examined the samples both in a dry state and in an aqueous environment," says Dr. Maria Eleonora Temperini, first author of the study.
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