Fluorescence, a phenomenon in which things emit light of longer wavelengths after the absorption of it, is increasingly used in various fields and techniques (e.g. medicine, biomedicine, molecular biophysics etc.). One of the methods in which fluorescence is used and its characteristics are exploited is confocal fluorescent microscopy of living cells. The mentioned method has many advantages over optical microscopy, among which the most important are better resolution and contrast of the obtained images. In order to use fluorescence for live-cell imaging, fluorescent probes need to be added to the sample - the molecules that fluoresce and localize among cell organelles. There are currently numerous commercial fluorescent probes but many of them are also being synthesized with the intention of improving their performance. For the proper use of a fluorescent probe, it is important to know, among other things, its toxicity, proper concentration area and the redistribution of the probe among cellular organelles, which we have determined in this master's thesis for selected probes - the four commercial ones and the four probes that were synthesized on University of Ljubljana Faculty of Pharmacy. In three out of four commercial probes, we were able to obtain the correct concentration range of use in which the probes can be used for long-term live-cell imaging. At these fluorescent test concentrations, there is at the same time an appropriate signal with respect to the signal-to-noise ratio and high cell viability (>90 %). Also, two of the four newly synthesized probes are also suitable for the long-term microscopy of living cells while the remaining three after four hours of incubation showed toxic effect on cells at the concentrations required for visualization and therefore cannot be used for the long-term live-cell imaging.
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