Novel imaging method: ‘Observing two different regimes simultaneously’

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UNIST team led by Prof. Jung-Hoon Park, develops new method employing adaptive structured illumination to simultaneous observe fast fluid dynamics and sub-diffraction limited subcellular organelle structural changes.  

Observation of sub-diffraction limited super-resolution images of live cells and fast dynamic interactions with their environment such as blood flow is now possible due to the development of a novel imaging technique enabling the observation of fine processes using high ‘spatial resolution’ and observing fast dynamic processes by tracking small time sequences for high ‘temporal resolution’.

Journal cover of August issue of Optica.
Tunable SIM allows high spatial resolution of cellular imaging with high temporal resolution of continuous fluid.

A UNIST research team in the biomedical engineering department led by Jung-Hoon Park has developed a technique realizing the high resolution of structured illumination microscopy and widefield fast temporal imaging simultaneously inside a single image. By controlling the illumination light pattern at different regions of interest in a custom fashion, different imaging properties could be obtained. Using this technique, fast processes such as calcium signaling and fine spatial changes due to these perturbations may now be possible.

Light microscopy uses visible wavelengths to magnify small objects for high resolution imaging. Although their resolution cannot quite reach those obtainable using electron microscopy, light microscopy can obtain 3D information of living cells.

Structured illumination microscope is a superresolution imaging technology that utilizes specifically designed illumination to obtain Morie interference patterns between the object and the illumination pattern. Using the know illumination pattern, fine structures beyond the diffraction limit can be obtained after signal processing. Complex sample preparation steps are not needed and the method is gentle on the sample enabling extended observation times. But since multiple images are required to obtain a single superresolved image, there is a tradeoff in temporal resolution.

Simulation results showing enhanced spatiotemporal resolution of Tunable SIM

The team solved this problem by designing illumination patterns that can adapt to the characteristics of the sample of interest. Using this approach, cancer cells cultured in a flowing fluid and minute changes due to their interaction could be observed. For the regions of interest that required fast temporal sampling, a constant illumination was imposed, while for regions of interest where high resolution was needed, a structured temporally changing illumination was imposed. While observation of widefield fast imaging or slow superresolution imaging was possible for the entire field of view, this is the first demonstration of selectively choosing different parts of the field of view for different imaging characteristics simultaneously.

Schematic illustration of the experimental setup

Our new method enables observation of varying dynamics across both space and time using a single imaging system. Observing cell/environment interactions using microfluidic platforms or observing fast dynamics such as calcium signaling or action potentials and related ~100 nanometer structural changes will be possible using this platform’ said Prof. Jung-Hoon Park.

This work which was performed with UNIST BME Prof. Joo Hun Kang, Su Hyun Jung, Cheolwoo Ahn, Byungjae Hwang was published in Optica as the cover article for the 2020 August issue and was supported by National Research Foundation and Posco TJ Park Foundation.

Taeseong Woo et al., Tunable SIM: observation at varying spatiotemporal resolutions across the FOV, Optica, https://doi.org/10.1364/OPTICA.392800