The chemical images of the insides of the bacteria were 30 times sharper than images from conventional mid-infrared microscopes. Researchers at the University of Tokyo have developed an advanced mid-infrared microscope that allows them to view structures inside living bacteria at the nanometer scale. Mid-infrared microscopy is generally limited by low resolution, especially compared to other microscopy techniques.

This latest development produced 120-nanometer images; The researchers say this is a thirty-fold improvement in the resolution of typical mid-infrared microscopes. Being able to see samples more clearly at such a small scale could help many areas of research, including infectious diseases, and pave the way for developing more accurate mid-infrared images in the future.

The microscopic realm is where viruses, proteins and molecules live. Thanks to modern microscopes, we can look down and see the inner workings of our own cells. But even these impressive tools have their limitations. For example, high-resolution fluorescence microscopes require samples to be labeled with fluorescence. Sometimes this can be toxic to the samples, and prolonged exposure to light during imaging can discolour the samples, meaning they are no longer usable. Electron microscopes can also provide impressive detail, but live samples must be placed in a vacuum before they can be examined.

Advantages of mid-infrared microscopy

In contrast, mid-infrared microscopy can provide both chemical and structural information about living cells without the need to stain or damage them. However, due to its relatively low solubility, its use in biological studies has been limited. While high-resolution fluorescence microscopy can narrow images down to tens of nanometers (1 nanometer equals one-millionth of a millimeter), mid-infrared microscopy can typically only reach about 3 microns (1 micron equals one-thousandth of a millimeter).

But in a new breakthrough, researchers at the University of Tokyo have managed to achieve higher resolution mid-infrared microscopy than ever before. “We achieved a spatial resolution of 120 nanometers, or 0.12 microns. This astonishing resolution is about 30 times better than conventional mid-infrared microscopy,” explained Professor Takuro Ideguchi from the Institute of Photonics Science and Technology at the University of Tokyo.

The team used “synthetic aperture,” a technique that combines multiple images taken at different lighting angles to create a sharper overall picture. As a rule, the sample is placed between two lenses. But lenses mistakenly absorb some of the mid-infrared light. They solved this problem by inserting a bacterial sample (used) coli And rhodococ jostii RHA1) on a silicon wafer that reflects visible light and transmits infrared light. This allowed the researchers to use a single lens, allowing them to better illuminate the sample with mid-infrared light and obtain a more detailed image.

“We were surprised at how clearly we could observe the intracellular structures of bacteria. The high spatial resolution of our microscope could allow us to study, for example, antimicrobial resistance, which is a global problem,” said Ideguchi. “We believe that we can continue to improve the technique in various directions. If we use a better lens and shorter wavelength visible light, the spatial resolution can be even below 100 nanometers. We want to examine different cell samples with extreme clarity to solve fundamental and applied biomedical problems.”