“Flashes of light” to catch electrons moving in biological molecules

At the Institute of Photonics and Nanotechnology (IFN-CNR), we have developed a tool to follow with extremely high temporal resolution the movement of electrons in molecules of biological interest. By using “flashes of light”, it has been possible to track in real-time the electron dynamics occurring in amino acids (building blocks of proteins) after interaction with ionizing radiation. The measured electronic motion is the fastest process ever observed in a biological structure.

Attosecond Laboratory. Credit: IFN-CNR and Politecnico di Milano.

Attosecond Laboratory. Credit: IFN-CNR and Politecnico di Milano.

Explaining how electrons move on the nanoscale is crucial for understanding a number of processes of biological relevance such as photosynthesis, cellular respiration or electron transport along large peptides and proteins. Moreover, the interaction of ionizing radiation with DNA triggers an ultrafast charge dynamics, which is responsible for damage of the DNA and ultimately cell death. Targeting DNA with ionizing radiation is a technique exploited in radiotherapy to treat cancer. Therefore, understanding the role of the electronic motion in the photo-chemistry of our own DNA could have a strong impact in radiotherapy and cancer treatment.

The “flashes of light” used for this research are obtained starting from a laser delivering few-femtosecond (milion billionths of a second) infrared pulses. These laser pulses are then converted in few-hundred attosecond (billion billionths of a second) pulses in the extreme ultraviolet (XUV) spectral region exploiting a process named High-order Harmonic Generation (HHG). In the HHG process an electron is ionized from an atom by a high-energy infrared laser pulse, the laser pulse then drives back the electron to the parent ion and the subsequent recollision releases a high-energy flash of light. These ultrafast light transients are then used to shine isolated biomolecules produced by evaporation in the gas phase and a subsequent ultra short laser pulse allows us to take “snapshots” of the charge moving along the molecular backbone. The developed experimental setup is the result of a fruitful collaboration between researchers from IFN-CNR, Milan, Italy, Politecnico di Milano, Milan, Italy and Queen’s University, Belfast, UK. The results of this research have been recently published in the prestigious journal Science.

Scheme of the experimental setup used to take “snapshots” of the electrons moving in the amino acid Phenilalanine. Credit: Francesca Calegari -www.mi.ifn.cnr.it/research/ultrafast/attosecond_physics.

Scheme of the experimental setup used to take “snapshots” of the electrons moving in the amino acid Phenilalanine. Credit: Francesca Calegari -www.mi.ifn.cnr.it/research/ultrafast/attosecond_physics.

This research will hopefully provide new important outcomes for Photonics and in particular for the emerging field of Attosecond Science. Attosecond science seeks understanding the key role of the light induced electronic motion in chemistry, biology and nanotechnology. This research is at the very early stages, however important implications can be foreseen in the fields of photo-chemistry and photo-biology, with tremendous prospects in phototherapy.

More Information

  1. Calegari et al., Science 346, 336 (2014)
  2. Chang, Fundamentals of Attosecond Optics, CRC Press (2011)
  3. Krausz and M. Ivanov, Rev. Mod. Phys. 81, 163 (2009)


calegariFrancesca Calegari received the Ph.D. in Physics from Politecnico di Milano in 2009. She was Postdoctoral Researcher with INFM and Politecnico di Milano until 2011. Since 2012 she has a permanent position as a Researcher at CNR-IFN, Milan, and she is contract Professor of Physics at Politecnico di Milano. From July 2014 till March 2015 she was visiting scientist at MPSD-CFEL, Hamburg, Germany. She works in the field of attosecond science and she is co-author of more than 50 research papers in international journals. Dr. Calegari was awarded an European Research Council (ERC) Starting Grant in 2014.


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