Optical trapping of lipid bodies reveals increased cytoplasm viscosity in Candida tropicalis post antimicrobial photodynamic therapy

Abstract Antimicrobial photodynamic therapy (aPDT) is a common treatment for large cell colonies, but its effectiveness is typically assessed through colony-forming unit counting, which lacks microscopic details about cell death. This study monitors the trap stiffness of optically trapped lipid bodies of C. tropicalis of approximately 1 μ m of radius following aPDT treatment. Methylene blue served as the photosensitizer at 20 μ M concentration, with a lethal light dose of 60 J cm −2 The results revealed a significant increase in viscosity after aPDT treatment. Additionally, image analysis confirmed substantial morphological changes indicative of cell death. These findings demonstrate the potential of optical tweezers as a non-invasive tool for assessing cellular health by providing both functional (viscosity) and morphological data on the response to aPDT.