Making sense of luminescence from GRAS optical probes

Fisetin-Mediated Perturbations of Membrane Permeability and Intracellular pH in Candida albicans

The antifungal activity of fisetin against Candida albicans is explored, elucidating a mechanism centered on membrane permeabilization and ensuing disruption of pH homeostasis. The Minimum Inhibitory Concentration (MIC) of fisetin, indicative of its interaction with the fungal membrane, increases in the presence of ergosterol. Hoechst 33342 and propidium-iodide staining reveal substantial propidium-iodide accumulation in fisetin-treated C. albicans cells at their MIC, with crystal violet uptake assays confirming fisetin-induced membrane permeabilization. Leakage analysis demonstrates a significant release of DNA and proteins in fisetin-treated cells compared to controls, underscoring the antifungal effect through membrane disruption. Green fluorescence, evident in both the cytoplasm and vacuoles of fisetin-treated cells under BCECF, AM staining, stands in contrast to controls where only acidic vacuoles exhibit staining. Ratiometric pH measurements using BCECF, AM reveal a noteworthy reduction in intracellular pH in fisetin-treated cells, emphasizing its impact on pH homeostasis. DiBAC4(3) uptake assays demonstrate membrane hyperpolarization in fisetin-treated cells, suggesting potential disruptions in ion flux and cellular homeostasis. These results provide comprehensive insights into the antifungal mechanisms of fisetin, positioning it as a promising therapeutic agent against Candida infections.

Temperature-dependence of riboflavin phosphorescence in cryosolvents

The molecular mobility of amorphous excipients is important for the stability of biomaterials during preservation, facilitating matrix formulation and product design. Phosphorescence spectroscopy is a sensitive optical method to study molecular mobility. However, there is a need to expand the pool of probes available for analysis since molecules differ in sensitivity. This research explored the feasibility and limitations of using riboflavin as a phosphorescent probe for monitoring matrix molecular mobility. Phosphorescence decays of riboflavin in four amorphous cryosolvents (aqueous solutions of glycerol, ethanol, sucrose, and dextran) were collected at 77 K to capture its natural phosphorescence lifetime (estimated at 170 ms). Decays were also collected during ballistic heating to assess the sensitivity of riboflavin towards changes in matrix molecular mobility. Riboflavin exhibited good sensitivity towards matrix secondary relaxations in the glass, indicating that riboflavin has excellent potential as an edible phosphorescent probe for molecular mobility in food and pharmaceutical products.