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In response to heat stress, triggered by a temperature increase of just a few degrees, cells activate a mechanism called the heat-shock response. While conventional global heating processes lead to an overall and slow increase of the temperature, heating processes based on laser illumination enable to achieve fast dynamics on the sub-second time-scale and spatially localized.
Thermal imaging using quadriwave lateral shearing interferometry (TIQSI) has been developped by Institut Fresnel in collaboration with PHASICS SA [1]. By quantitatively measuring the transmitted phase this approach is able to measure temperature fields at the microscopic level from thermal-induced refractive index changes of the medium surrounding laser-illuminated plasmonic nanoabsorber. Phase, intensity and temperature images are measured in parallel thanks to a quadriwave lateral shearing interferometry SID4BIO camera, developed by PHASICS.
We propose in this article to study the dynamics of the heat-shock response of living cells by using a TIQSI system. A dynamic control heat stress is induced to retinal pigmented epithelial (RPE) cells by illuminating gold nanoparticles used as nanosources of heat [2]. Intensity images of the heat-shock transcription factors (HSF) of cells fluorescently labelled observed in parallel to the heating process reveal the formation of fluorescent granules within the nucleus, a sign of cellular heat-shock response.
By heating successively the RPE cells for different laser powers, we measure rise-time and dynamic of the heat-shock for different magnitudes of the stress response.
[1] Baffou, G., Bon, P., Savatier, J., Polleux, J., Zhu, M., Merlin, M., ... & Monneret, S. (2012). Thermal imaging of nanostructures by quantitative optical phase analysis. ACS nano, 6(3), 2452-2458.
[2] Robert, H.M.L, Savatier, J., Vial, S., Verghese, J., Wattellier, B., … & Baffou, G. (2018) Small, 1801910
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