Highly visible photoluminescence in biocompatible liquids obtained by rehydration of Saccharina latissima algae at room temperature

The rehydration process of air-dried algae Saccharina latissima, obtained with distilled water and/or with phosphate-buffered saline solution (PBS), led to the formation of a highly photoluminescent liquid. The structure-function relationships for the bioactivities of these algae are still little known and undisclosed. The aim of this work is twofold: to describe the surprising behavior of the Saccharina latissima when it is rehydrated at room temperature and to attempt its release in liquids that appear photoluminescent under UV excitation. Rehydration seems to release nanometric-sized molecules into the liquid, making it absorbent in the near UV. Polysaccharides and phenols, released by the algae, act as quantum dots dispersed in the liquid. The absorption of UV light by the liquid, at 365 nm, induces luminescence in the visible wavelength region with high emission in the blue band, around 478 nm. Further release removes larger nanoparticles that emit first in the green-yellow regions and subsequently in the brown-orange-red regions. Characterization measurements of the biocompatible luminescent liquid were performed by considering optical spectroscopies in the UV, Visible, and IR ranges, and electron microscopy. Possible applications, such as bioimaging, diagnostics, and therapy, together with the possibility to realize luminescent films and devices, are proposed, and some are described as well.