Quantum Imaging of Tissue Samples

Quantum imaging setup for the microscopic examination of cancer cells. (Source: Fh.-IOF)

While optical analysis techniques such as micro­scopy and spectro­scopy are extremely efficient in visible wavelength ranges, they quickly reach their limits in the infrared or terahertz range. That, however, is precisely where valuable infor­mation is hidden. For example, bio-substances such as proteins, lipids and other bio­chemical components can be distin­guished based on their charac­teristic molecular vibra­tions. These vibrations are stimulated by light in the mid-infrared to terahertz range and are very difficult to detect with conven­tional measure­ment techniques. “If these motions could be captured or induced, it would be possible to see exactly how certain proteins, lipids and other substances are distributed in cell samples. For example, some types of cancer have a charac­teristic concen­tration or expression of certain proteins. This would mean that the disease could be detected and treated more effi­ciently. More precise knowledge of the distri­bution of bio-substances could bring major advances in drug research, as well,” says quantum researcher Markus Gräfe from Fraunhofer IOF.

But how can infor­mation from these extreme wave­length ranges be made visible? The quantum mechanical effect of photon ent­anglement is helping the researchers allowing them to harness twin beams of light with different wave­lengths. In an inter­ferometric setup, a laser beam is sent through a nonlinear crystal in which it generates two entangled light beams. These two beams can have very different wave­lengths depending on the crystal’s properties, but they are still connected to each other due to their entangle­ment.

“So now, while one photon beam in the invisible infrared range is sent to the object for illumination and interaction, its twin beam in the visible spectrum is captured by a camera. Since the entangled light particles carry the same infor­mation, an image is generated even though the light that reaches the camera never inter­acted with the actual object,” explains Gräfe. The visible twin essen­tially provides insight into what is happening with the invisible twin.

The same principle can also be used in the ultra­violet spectral range: UV light easily damages cells, so living samples are extremely sensitive to that light. This signi­ficantly limits the time available for inves­tigating, for instance, cell processes that last several hours or more. Since less light and smaller doses of radiation pene­trate tissue cells during quantum imaging, they can be observed and analyzed at high resolution for longer periods without destroying them.

“We are able to demons­trate that the entire complex process can be carried out in a way that is robust, compact and portable,” says Gräfe. The researchers are currently working to make the system even more compact, shrinking it to the size of a shoebox, and to further enhance its resolution. The next step they hope to achieve is, for example, a quantum scanning micro­scope. Instead of the image being captured with a wide-field camera, it will be scanned, similar to a laser-scanning micro­scope. The researchers expect this to yield even higher resolutions of less than one micrometer, enabling the examina­tion of structures within individual cells in even greater detail. On average, one cell measures roughly ten micro­meters in size. In the long term, they want to see quantum imaging inte­grated into existing micro­scopy systems as a basic technology, thus lowering the barriers for industry users. (Source: Fh.-IOF)

Links: Optical Quantum Technologies, Fraunhofer Institute for Applied Optics and Precision Engineering IOF, Jena, Germany • Fraunhofer Lighthouse Project QUILT, Jena & Freiburg, Germany

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