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Intracellular lasers: Coupling of optical resonances with biological processes

Periodic Reporting for period 1 - Cell-Lasers (Intracellular lasers: Coupling of optical resonances with biological processes)

Reporting period: 2020-05-01 to 2021-10-31

The goal of the Cell-Lasers project is to develop and embed several types of lasers into cells to study the cell biology to an unprecedented accuracy and multiplexing ability.
The specific objectives are to study
• forces acting within cells,
• properties of natural cavities in lipid droplets and
• intracellular chemical environment.

In the long term Cell-Lasers aims to transform the bio-integrated lasers from being a pure scientific curiosity into powerful tool for the study of biophysical and biochemical processes taking place on a single cell level. Cell-Lasers will significantly improve measurement of several biochemical and biophysical parameters inside cells. By elucidating processes in cells which also lead to diseases, Cell-Lasers will have a strong and long-term impact on medical and social level, by improving quality of life. Lasers inside cells are also very interesting to broad audience and can have large media impact.
Interfacial tension is important in a number of biological processes. Therefore, a precise in situ measurement of interfacial tension is very important. A simple, fast and very precise technique to measure interfacial tension between two immiscible liquids based on optical resonances was demonstrated (Fig. 1). A microdroplet is generated at the end of a glass microcapillary, submerged in a continuous liquid phase, and its size changes are monitored with nanometer precision via the optical resonances, while simultaneously applying finely tunable pressure through the microcapillary. Interfacial tension was determined from the size of the droplet and the pressure in the microcapillary at equilibrium. Droplets as small as 8 microns were used, thus requiring extremely small sample volume.

The results of this study were published in a peer reviewed article: Gregor Pirnat, and Matjaž Humar, Whispering Gallery-Mode Microdroplet Tensiometry, Advanced Photonics Research, DOI: 10.1002/adpr.202100129



Coupling of light with the complex soft matter structures inserted into a laser cavity was studied into detail. This study provides experimental and simulation insights into this coupling. Complex tunable microlasers emitting structured light were made from self-assembled topological LC superstructures containing topological defects inserted into a thin Fabry-Pérot microcavity (Fig. 2). The topology and geometry of the LC superstructure determine the structuring of the emitted light by providing complex three dimensionally varying optical axis and order parameter singularities, also affecting the topology of the light polarization.

The results of this study were published in a peer reviewed article: Miha Papič, Urban Mur, Kottoli Poyil Zuhail, Miha Ravnik, Igor Muševič, and Matjaž Humar, Topological liquid crystal superstructures as structured light lasers, Proceedings of the National Academy of Sciences, DOI: 10.1073/pnas.2110839118
The work will continue on all three main objectives:
• forces acting within cells,
• properties of natural cavities in lipid droplets and
• intracellular chemical environment.

On all of these three topics we already have very promising results. Some of the results are already summarized in manuscripts and already in review as a peer reviewed article or to be submitted soon.
Figure shows the experimental configuration of a complex soft matter laser.
Figure shows the principle of interfacial tension measurement.