Gold nanoparticles enhance methylene blue– induced photodynamic therapy: a novel therapeutic approach to inhibit Candida albicans biofilm

Shakir Khan,¹ Fahad Alam,² Ameer Azam,2 Asad U Khan<sup>1

1</sup>Interdisciplinary Biotechnology Unit, ²Center of Excellence in Material Science (Nanomaterials), Aligarh Muslim University, Aligarh, India

Abstract: This article explores the novel gold nanoparticle–enhanced photodynamic therapy of methylene blue against recalcitrant pathogenic Candida albicans biofilm. Physiochemical (X-ray diffraction, ultraviolet-visible absorption, photon cross-correlation, FTIR, and fluorescence spectroscopy) and electron microscopy techniques were used to characterize gold nanoparticles as well as gold nanoparticle–methylene blue conjugate. A 38.2-J/cm² energy density of 660-nm diode laser was applied for activation of gold nanoparticle–methylene blue conjugate and methylene blue against C. albicans biofilm and cells. Antibiofilm assays, confocal laser scanning, and electron microscopy were used to investigate the effects of the conjugate. Physical characteristics of the gold nanoparticles (21 ± 2.5 nm and 0.2 mg/mL) and methylene blue (20 µg/mL) conjugation were confirmed by physicochemical and electron microscopy techniques. Antibiofilm assays and microscopic studies showed significant reduction of biofilm and adverse effect against Candida cells in the presence of conjugate. Fluorescence spectroscopic study confirmed type I photo toxicity against biofilm. Gold nanoparticle conjugate–mediated photodynamic therapy may be used against nosocomially acquired refractory Candida albicans biofilm.

Keywords: Candida biofilm, gold nanoparticle–methylene blue conjugate, photodynamic therapy