University of Tokyo nanoscope sees structures within bacteria

23 Apr 2024

New technique set to improve research into bacteria behavior and infectious diseases.

A project at the University of Tokyo has developed a mid-infrared microscopy platform offering an improved view of structures inside living bacteria.

Described in Nature Photonics, the new nanoscope should assist research into infectious diseases as well as opening routes to more accurate mid-infrared imaging in other fields.

A number of high-resolution or super-resolution methods have been applied to the imaging of living bacteria, in order to better understand the complex cellular environment within them and the ways that individual proteins in bacteria behave.

Examples have included the combination of super-resolution fluorescence microscopy and cryogenic electron tomography (CET) developed by Stanford University in 2020, intended to image biomolecules of interest within their own cellular neighborhood and described as "a big leap for biology" at the time.

However, super-resolution fluorescent microscopes require the use of added label molecules, bringing with them potential problems of toxicity and extended light exposure. Mid-infrared techniques are a promising alternative, but have usually been limited to relatively low imaging resolutions.

The Tokyo project's solution involves improving the resolution of a mid-IR platform using a synthetic aperture, a technique combining several images taken from different illuminated angles to create a clearer overall picture, and doing so using a single lens rather than sandwich a sample between two lenses.

This architecture allows the desired sample of bacteria to be placed on a silicon plate, which reflects visible light and transmitted infrared light with just one lens in the system.

Understanding antimicrobial resistance

This single-lens approach combined with quantitative phase imaging is "an optimal implementation of wide-field mid-IR photothermal imaging to achieve high spatial resolution," said the project in its published paper. In trials using E. coli and Rhodococcus jostii RHA1 bacteria, the platform did indeed allow significantly improved resolution of the bacteria's internal structures.

"We achieved a spatial resolution of 120 nanometers or 0.12 microns," commented Takuro Ideguchi from the Institute for Photon Science and Technology (IPST) at the University of Tokyo. "This amazing resolution is roughly 30 times better than that of conventional mid-infrared microscopy."

Future developments of the same approach, such as using a shorter visible wavelength and/or a higher objective numerical aperture, could allow the device to achieve sub-100-nanometers spatial resolution, which would pave the way for mid-IR wide-field nanoscopy as a more common tool in biological imaging. Resolutions in that range should help researchers to understand antimicrobial resistance, addressing a major global health challenge.

"We were surprised at how clearly we could observe the intracellular structures of bacteria," said Takuro Ideguchi. "If we use a better lens and a shorter wavelength of visible light, the spatial resolution could even be below 100 nanometers. With superior clarity, we would like to study various cell samples to tackle fundamental and applied biomedical problems."