Highly yield of blue photoluminescence in rehydrated Sargassum muticum algae at room temperature

The rehydration process of air-dried algae Sargassum muticum using distilled water produces a highly blue photoluminescent liquid under UV excitation. The cause of this effect is the release of small nanoparticles and molecules exhibiting quantum dot behavior, which are strongly absorbent in the near-UV region and emit visible luminescence. The aim of this work is twofold: to describe the surprising behaviour of the Sargassum muticum algae when they are rehydrated at room temperature, determining their molecular release in water, and to examine their molecules and small released aggregates that appear photoluminescent under UV excitation. Rehydration appears to cause the release of nanometric-sized molecules into the liquid, primarily due to polysaccharides and phenols, i.e., hydrocarbon nuclei released by the algae, which act as quantum dots dispersed in the liquid. The absorption of UV light at 365 nm induces luminescence in the visible wavelength region with high emission in the blue band, around 478 nm. Characterization measurements of the biocompatible luminescent liquid were performed using optical spectroscopy in the UV, Visible, and IR ranges, as well as optical and electron microscopy. Possible applications of such a liquid, including bioimaging, diagnostics, and therapy, as well as the potential to create luminescent films and devices, are proposed, and some are described.