Surface alteration of Candida albicans after antifungal photodynamic therapy: A Raman spectroscopic study

Candida albicans surface alterations following photodynamic therapy using Raman spectroscopy were studied. Previously effective photosensitizers were tested: 200 μM erythrosine, 100 mM KI, 200 μM erythrosine+100 mM KI irradiated with a 530 ± 10 nm LED (250 mW/cm², 20 J/cm² per session for two sessions (total fluence: 40 J/cm²)), 60 M bisdemethoxycurcumin irradiated with a 430-480 nm LED (950 mW/cm², 75 J/cm²), 100 μM melatonin irradiated with a 630 ± 10 nm LED (250 mW/cm², 75 J/cm²), and 60 μM bisdemethoxycurcumin+100 μM melatonin with dual light. Treatments were applied to mature C. albicans biofilms. Negative and positive controls were phosphate-buffered saline and nystatin, respectively. Raman spectroscopy used a 50× objective lens, 600 lines/mm grating, and 785 nm laser. Data were analyzed using principal component analysis. Erythrosine and erythrosine+KI induced specific surface alterations with Raman peaks similar to nystatin and differing from the negative control at 625, 1159, 1270, 1336, 1491, and 1603 cm^-1.Raman peaks at 625 cm^-1 correspond to phenylalanine, 1159 cm^-1 to carbohydrate, 1270 cm^-1 to amide III, 1336 cm^-1 to proteins and carbohydrate, 1491 cm^-1 to nucleic acid bases, and 1603 cm^-1 to ergosterol. Other treatment groups showed no differences from the negative control. Erythrosine and erythrosine+KI exhibited similar mechanistic cell surface alterations to nystatin.