In the Estonian national student research competition, TalTech doctoral student and Metrosert researcher Matt Rammo received third prize in the field of natural sciences for his doctoral thesis “Two-photon Absorption Spectroscopy as a New Quantitative Protonation Probe”.

Matt Rammo explains the content of his research in more detail:

In everyday life, one-photon absorption is quite understandable, such as the creation of the sense of vision when light enters the human eye. This is a highly probable and well-studied process, as most life on Earth is based on one-photon absorption: plant photosynthesis, plankton growth in the world’s oceans, and more.

Much rarer are multi-photon processes, which require photons to converge in a strong radiation field at the same spatial point in the material being studied. Care must be taken to ensure the material at this point does not evaporate – therefore, it is important that the light travels in pulses (allowing the material to cool between pulses) and that the shape of the pulse is known. When all conditions are met, it is possible to determine the unique fingerprint of the material – by measuring the cross-sectional area of absorption through the weak fluorescence resulting from multi-photon absorption.

Although the first scientific studies on two-photon absorption appeared in the 1930s, it was only with the advent of lasers that opportunities for a more thorough investigation of this process emerged. Since measurements of two-photon absorption spectra are very labor-intensive and experimentally complex, the results are often highly uncertain.

In this dissertation, a femtosecond pulse laser-based spectrometer developed from the research was used, allowing for automated measurement of fluorescence induced by two-photon absorption, achieving very high accuracy. For the first time, two newly synthesized groups of molecules were studied.

Firstly, it was demonstrated how the addition of acid to a dye solution caused significant changes in the fluorescence properties. Thanks to very thorough characterization, these molecules can be used as cell membrane-specific pH probes.

Secondly, modified symmetrical pyrrolopyrrole molecules were studied, which contribute to the formation of vitamin B12, for example. It was found that the attachment of a proton to the molecule caused a symmetry break and an increase in the cross-section of two-photon absorption (known as the Laporte rule). Upon second protonation, the symmetry of the molecule was restored. Such two-photon absorption spectra could be measured for the first time thanks to the developed spectrometer. An explanation was also provided for the weak absorption in the two-photon absorption region, where it should be forbidden due to symmetry. The relationship between environmental pH and the measured two-photon absorption spectra created by the measurements allows for optical measurements to quantify pH.

The field of two-photon absorption spectroscopy is continuously evolving, including improvements in measurement techniques, apparatus, and the ability to interpret results. In addition to fundamental scientific research, this field has found practical applications, such as in live cell microscopy, medical applications like phototherapy, and commercial 3D printers.

This research significantly contributed to the development of two-photon absorption spectroscopy measurement methodology and apparatus and expanded our fundamental knowledge in this field.

You can learn more about the work in the TalTech Library digital collection at the following link: https://digikogu.taltech.ee/et/Item/f9c53f09-f44d-431c-9c3d-5858e514a3a4

At Metrosert, Matt Rammo is part of the research and development division and focuses on the development of optics.

We congratulate Matt Rammo!

The student research competition is organized by the Estonian Research Council in collaboration with the Ministry of Education and Research.