"Ghost imaging" technology enables ultra-high-resolution imaging of moving objects

Super-Resolution Microscopy: Capturing Live Cell Dynamics at Nanoscale

Super-resolution microscopy, also known as nanoscopy, achieves nanoscale resolution by overcoming the diffraction limit of light. While nanoscopes can capture images of individual molecules within cells, their application to live-cell imaging has been challenging. This is because it typically requires hundreds or thousands of imaging windows to reconstruct an image, making the process too slow to capture rapidly changing dynamic processes. Now, a new nanoscopy technique promises to capture biological processes occurring inside cells at sub-millisecond speeds. Researchers have utilized advanced imaging methods to achieve super-resolution microscopy at unprecedented speeds. The new method can capture previously unattainable details in live cells.

Researchers from the Chinese Academy of Sciences published a paper in 'Optica' using an unconventional 'ghost imaging' method to increase the imaging speed of nanoscopes. This combination yields nanoscale resolution with fewer imaging windows compared to traditional nanoscopy techniques. This imaging method can potentially probe the dynamics occurring in subcellular structures at a millisecond temporal resolution and a nanoscale spatial resolution of tens of nanometers.

New Technology Enables Faster Imaging

The new technology is based on Stochastic Optical Reconstruction Microscopy (STORM), one of the three super-resolution techniques that received the Nobel Prize in 2014. STORM, sometimes also called Photoactivated Localization Microscopy (PALM), is a field technique that uses fluorescent markers to switch between an emissive (ON) state and a dark (OFF) state. After hundreds or thousands of snapshots, each capturing a subset of fluorescent markers in the ON state at a given time, the position of each molecule can be determined and used to reconstruct a fluorescent image.

The researchers focused on how to use ghost imaging to accelerate the STORM imaging process. Individual light patterns do not carry any meaningful information about the object. However, ghost imaging forms an image by correlating a light pattern that interacts with the object with an uncorrelated reference pattern. The researchers also used compressed sensing, a computational method that uses an algorithm to fill in missing information, allowing images to be reconstructed with fewer exposures.

Shensheng Han, co-leader of the research team, stated, 'While STORM requires a low density of fluorescent markers and many image frames, our method can create high-resolution images using very few frames and a high density of fluorophores. It also doesn't require any complex illumination, which helps reduce photobleaching and phototoxicity that can damage dynamic biological processes and live cells.'

Enhancing Imaging Efficiency

To implement this new technology, the researchers used an optical component called a random phase modulator to transform the fluorescence from the sample into a random speckle pattern. By encoding the fluorescence in this way, each pixel of a fast CMOS camera can collect light intensity from the entire object in a single frame. To form an image through ghost imaging and compressed sensing, this light intensity is correlated with a reference light pattern in a single step, making image acquisition more efficient and reducing the number of frames required to form a high-resolution image.

The researchers tested the technique by imaging 60-nanometer rings. The new nanoscopy technique reconstructed the ring structure using only 10 image frames, whereas traditional STORM methods required up to 4,000 frames to achieve the same result. The new method also imaged a 40-nanometer ruler using 100 image frames.