Enhanced viral inactivation by photodynamic therapy using curcumin and methylene blue: An in vitro study with bacteriophage as a viral model

Abstract

The global spread of SARS-CoV-2 highlighted the urgent need for broad-spectrum antiviral strategies. One promising approach is antimicrobial photodynamic therapy (aPDT), which, in the presence of oxygen, suitable photosensitizers and irradiation, generates reactive oxygen species capable of inactivating a broad spectrum of viruses. In this work, in vitro aPDT assays were performed using curcumin (Cur) and methylene blue (MB) as biocompatible photosensitizers, with bacteriophage ZC01 serving as the viral model and irradiation at 450 nm and 660 nm. Bacteriophages are frequently used as robust viral models due to their structural tolerance to photodynamic treatments compared with many mammalian viruses. Under the experimental conditions employed, a high viral load (~109 PFU mL⁻¹) was used to represent a challenging inactivation scenario. The combination of curcumin and methylene blue at fluences of 12.5 and 25 J/cm² per wavelength produced viral load reductions of 7.01 log10 and 9.14 log10, respectively. These results indicate that Cur/MB combination can achieve efficient photodynamic viral inactivation under moderate irradiation fluences. This in vitro platform may contribute to the development of photodynamic antiviral strategies and provides a practical system for evaluating potential photosensitizers and irradiation conditions for viral photoinactivation.