A drop of liquid, a beam of light – and suddenly, an invisible signal appears. A research team from Leibniz IPHT and Leiden University has developed a novel sensor that could one day detect processes deep inside tissue that were previously hidden from view.

The sensor is based on triplet–triplet annihilation upconversion (TTA-UC), an optical mechanism in which two partner molecules absorb red light, transfer energy to a fluorescent molecule – and make it glow. In this way, low-energy red light is converted into high-energy blue light.

“With this new sensor, we can detect calcium ions precisely and sensitively, without the disadvantages of conventional methods such as weak signals or interfering background radiation,” explains Dr. Tingxiang Yang, who developed the technique as a doctoral researcher at Leibniz IPHT as part of the international LogicLab ITN training program.

Light That Reaches Deeper

The human body is like the deep sea – its interior lies in darkness. Conventional fluorescent probes require UV or blue light, which barely penetrates tissue. Red light, on the other hand, can penetrate several millimeters without disrupting cellular processes.

This is precisely where the new sensor comes in: It uses this principle to detect calcium ions in deeper cellular layers and thus makes it possible to observe biochemical processes previously hidden in the dark.

Looking Into Cells With Light

To understand and optimize the sensor’s mechanism, Tingxiang Yang used advanced spectroscopic methods. At Leibniz IPHT, she had access to high-precision measurement techniques specifically developed for light-active molecules.

Using absorption spectroscopy, she analyzed how her molecules absorb light. Fluorescence lifetime spectroscopy helped her determine how long the molecule emits light after excitation – an important indicator of the system’s efficiency. She also used transient absorption spectroscopy to observe the energy flow between molecules on the nanosecond scale.

These methods are not only essential for basic research but also have practical relevance for biomedical diagnostics. They make it possible to track molecular processes in real time.

From Jena to the World: LogicLab as a Launchpad

The international doctoral program LogicLab ITN, under which the research was conducted, was funded by the European Union. It brought together researchers from various disciplines to develop new types of molecular sensors for biomedicine. The aim was to design intelligent molecular switches capable of visualizing biological processes.

Tingxiang Yang found the interdisciplinary collaboration especially formative:
“Working with chemists, physicists, and biologists from across Europe gave me new perspectives. I learned how important it is to look beyond your own discipline.”

Her colleague from LogicLab, Dr. Keshav Kumar Jha, also benefited from this environment. While Yang’s work opened new paths for optical diagnostics, Jha studied similar light-driven processes in liposomes – tiny membrane vesicles – at Leibniz IPHT. His research contributed key insights into molecular dynamics in biological systems.

The project was initiated by Prof. Dr. Benjamin Dietzek-Ivanšić and later led by PD Dr. Martin Presselt. His company Sciclus supported the research with quantum chemical simulations to better understand the light-driven mechanisms in molecular systems. These calculations were performed by Soumik Ghosh, an external PhD student for LogicLab and Sciclus.

 

 

Publication
Andreeva, V. D. et al. (2024). Red-to-Blue Triplet–Triplet Annihilation Upconversion for Calcium Sensing. The Journal of Physical Chemistry Letters, 15(29), 7430–7435.
🔗 https://doi.org/10.1021/acs.jpclett.4c01528

 

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The human body is like the deep sea – conventional UV or blue light cannot penetrate it, but red light can. Researchers in the LogicLab ITN project have developed a sensor that detects calcium ions using light. How this works is illustrated in the animated film created for the project by aloopvideo.com, from which the shown illustration is taken. © Aloop