Quantum Ghost Imaging Safely Images Live Plants Using IR Light

Quantum ghost imaging (QGI), a technique that leverages quantum mechanics to capture images at extremely low light levels, could provide a way to image living plants without exposing them to harmful wavelengths. QGI also removes the need to insert dyes or other labels into plant specimens, further protecting these delicate samples.

Use of QGI for live plant imaging could foster the development of biofuel crops like sorghum, by contributing to the optimization of plant growth for maximum yield and sustainability.

A research group at Los Alamos National Laboratory (LANL) used nondegenerate QGI, an advanced form of QGI, to acquire images of living plants with light that was orders of magnitude below starlight. The researchers showed that QGI could be used for extremely low-light bioimaging and for imaging light-sensitive samples that require low-intensity illumination to prevent phototoxicity or sample degradation.

Principles of quantum ghost imaging (QGI). (Top) Sorghum plant and quantum ghost microscope image of a live sorghum leaf. Bright spots are rows of stomata. (Bottom) Binary test targets, including a ghost from Pac-Man and the LANL logo. Courtesy of Paul Ziomek, visual designer, and Duncan Ryan, scientist, Los Alamos National Laboratory.

The phenomenon of quantum entanglement makes it possible to use nondegenerate QGI to probe a sample at one wavelength and form the image of the sample with correlated photons at a different wavelength. One low-intensity color (the best match to the sample) is used, and a different color is used at a higher intensity to form the image of the sample. This spectral separation lessens the need for imaging detectors with high sensitivity in the NIR region, reducing the illumination intensity that is required.

The researchers developed a QGI microscope for label-free bioimaging. To improve image quality and contrast, they used NCam (Nocturnal Camera), a single-photon detector proficient in correlation. With NCam, they acquired images of living plants with as low as 1% light transmission, demonstrating nondegenerate QGI with outstanding sensitivity.

The plants imaged with this approach were exposed to just 3 attoWatts per square centimeter (3 aW/cm²) of light during imaging. IR)light was used to detect chemicals in the plants that could only be seen with IR wavelengths. NCam provided QGI with improved correlation metrics and noise suppression, compared to early QGI demonstrations and the most recent single-photon avalanche diode array experiments.

The researchers expanded their use of QGI from binary test targets to the imaging of thick, intact, undisturbed, and living plants including sorghum, rabbit foot fern, and cilantro leaf samples. When focusing on the plants’ water absorption feature in the NIR, the researchers achieved high-contrast images below 5% transmission. Stomata on plant leaves close at night to reduce water loss. The researchers noticed the stomata closing, due to the very low illumination intensity required for QGI.

To the best of the researchers’ knowledge, this is the first demonstration of QGI on complex living organisms. The QGI microscope does not require intrusive sample preparation like microsectioning. There is no need for labelling, which can interfere with plant processes.

With this work, the LANL team shows that practical bioimaging is possible with QGI. The use of QGI for capturing images of living plants could lead to the use of QGI-based NIR imaging in new application spaces where low-light conditions are crucial for maintaining sample integrity.

The research was published in Optica (www.doi.org/10.1364/OPTICA.527982).