Abstract
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•Effect of aggregation on singlet oxygen generation.•Singlet oxygen quantification using an optical dosimeter.•Xanthene-based photosensitizers.•Optimal concentration of photosensitizer for photodynamic therapy (PDT)•Solvent effect on singlet oxygen generation.
This study investigates the relationship between photosensitizer concentration and singlet oxygen (1O2) production, focusing on three xanthene-based dyes commonly used in photodynamic therapy (PDT): rose bengal (RB), erythrosin B (EB), and eosin Y (EY). 1O2 measurements were performed using an optical dosimeter capable of detecting 1O2 luminescence in the 1270–1280 nm infrared range in both ultra-pure water and saline (0.9 % NaCl) solutions for 10 concentrations ranging from 2.46 × 10-5 to 1.97 × 10-3 M. The results were fit with a model based on the Beer-Lambert law. Aggregation was quantified by analyzing the absorbance peak intensity ratios (measured using UV–vis spectroscopy). Our findings indicate that at lower concentrations (<2.46 × 10-4 M), 1O2 production increases with rising photosensitizer concentration until it reaches a peak and then decreases at higher concentrations, as predicted with the Beer-Lambert model. Additionally, an aggregation effect is detected at higher concentrations in ultra-pure water and more pronounced in saline solutions, where the hydrophobic nature of the photosensitizers leads to enhanced aggregation which also affects the 1O2 generation. These results underscore the importance of optimizing photosensitizer concentration and solvent selection to maximize 1O2 generated while minimizing aggregation. Understanding this balance is crucial for improving the efficacy of PDT in clinical use.