Effect of preirradiation time of erythrosine + potassium iodide‐mediated photodynamic therapy on candidal inhibition and singlet oxygen formation

We aimed to compare the anticandidal effect among different preirradiation times, measure singlet oxygen levels, and investigate the correlation between candidal reduction and singlet oxygen formation in erythrosine + KI photodynamic therapy. Candida albicans (ATCC10231) biofilms were treated with 100/200 μM erythrosine + 100 mM KI for 1, 3, or 5 min before light-emitting diode (520 ± 10 nm, 250 mW/cm², 20 J/cm²) irradiation. Phosphate-buffered saline, and nystatin were negative and positive controls, respectively. Candidal cells were quantified using a drop plate assay. Singlet oxygen was measured using a 9,10-dimethylanthacene probe at 375/436 nm emission/excitation wavelengths. Median candidal counts and singlet oxygen formation were compared using Kruskal-Wallis with Dunn test. A p-value <0.05 was considered significant. Spearman's correlation was used to correlate candidal reduction and singlet oxygen formation. All preirradiation times for 200 μM erythrosine + 100 mM KI decreased candidal cells by 7.59 (IQR = 0.33) log₁₀CFU/mL. At a 1-min preirradiation, this group significantly generated higher singlet oxygen than the positive control (p < 0.001). Singlet oxygen levels correlated mildly with candidal reduction in the lower erythrosine group but not the higher group, likely due to singlet oxygen saturation. A 1-min preirradiation with 200 μM erythrosine + 100 mM KI generates singlet oxygen to inhibit C. albicans biofilms and shows potential for clinical oral candidiasis treatment.