The effect of light source and fluence on the photodynamic response of RAW 264.7 macrophages containing indocyanine green-bovine serum albumin complexes.

Photodynamic therapy (PDT) efficacy depends on both the photophysical properties of the photosensitizer and the spectral characteristics of the irradiation source. In this study, the photodynamic response of RAW 264.7 macrophages incubated with an indocyanine green-bovine serum albumin (ICG-BSA) complex was evaluated using three irradiation sources: an 820 nm diode laser (emission maximum ~790 nm), a 660 nm diode laser, and a broadband tungsten-halogen OSL2 illuminator. The photophysical stability of the ICG-BSA complex was assessed by UV-Vis spectroscopy, while PDT activity was evaluated by cell viability and fluorescence measurements. The ICG-BSA complex exhibited good spectral stability and maintained characteristic absorption bands associated with monomeric and dimeric forms of ICG. Irradiation induced a fluence-dependent decrease in cell viability and fluorescence intensity, indicating effective photodynamic activation and photobleaching of the photosensitizer. The strongest photodynamic response was observed for the 820 nm laser, followed by the OSL2 illuminator, whereas the 660 nm laser produced the weakest effect. Increasing ICG concentration further enhanced photodynamic cytotoxicity under constant irradiation conditions. The results demonstrate that PDT efficiency is strongly influenced by spectral overlap between the irradiation source and the absorption characteristics of the ICG-BSA complex, highlighting the importance of excitation conditions in determining photodynamic activity.