Silver nanoprisms enhances in vitro photodynamic activity of methylene blue against Candida albicans

Introduction: Photodynamic therapy is a technique that uses a light source, a photosensitizer (PS), and molecular oxygen to produce reactive oxygen species, which promote fatal cell/tissue damage. The association of metallic nanosystems to PS species may enhance their energetic output by surface plasmonic effects. This process is related to the collective oscillation of electrons on the surface of the metallic nanoparticles, which depends on their size and shape, and on the spectral arrangement accomplished. Here we applied silver nanoprisms to enhance PS activity of Methylene Blue (MB), a known PS.

Methodology: Candida albicans fungi were grown in sabouraud agar and standardized to 10⁶ CFU/mL. Inactivation experiments were performed by applying MB (50 mmol.L^-1) and a conjugate containing 35-40 nm Ag nanoprisms (extinction band at 664 nm) electrostatically associated to MB (to same final concentration). The irradiation time was 3 and 6 min (radiant exposure of ca 8 and 16 J.cm^-2, respectively).

Results and discussion: Irradiation with 3 or 6 min with MB only was not able to promote fungal death, while this phenomenon was observed for the conjugate, at 6 min irradiation time. When compared to other studies described in the literature, we have applied a lower dose of MB which we suggest results from plasmonic enhancement.

Conclusion: MB conjugated to nanoprisms enhanced in vitro inactivation of C. albicans, with a relatively short irradiation time and we suggest that this PS-metallic combination enhances antifungal therapeutic.