Investigation of Viscoelastic Properties of Macrophage Membrane–Cytoskeleton Induced by Gold Nanorods in Leishmania Infection

Cell membranes and the cytoskeleton play crucial roles in the regulation of cellular responses by mediating mechanical forces and physical stimuli from the microenvironment through their viscoelastic properties. Investigating these properties provides valuable insights into disease mechanisms and therapeutic strategies. Gold nanorods (GNRs), especially under irradiation, exhibit lethal effects against Leishmania parasites through plasmonic photothermal conversion. In this study, we focus on evaluating the effects of non-irradiated GNRs on macrophage properties to better understand their intrinsic interactions with cells and support the development of future phototherapy applications. Here, defocusing microscopy (DM), a quantitative phase microscopy technique, was used to analyze membrane fluctuations in macrophages (M∅s) exposed to GNRs (average length of 43±8 nm and diameter of 20±4 nm) and infected with Leishmania amazonensis. By quantifying membrane–cytoskeleton fluctuation from defocused images, we extracted viscoelastic parameters, including bending modulus (kc) and viscosity (η), to characterize membrane behavior in detail. Our results show that infection increases both kc and η, while treatment at IC50 reduces infection and selectively increases kc without affecting η. In healthy macrophages, exposure to GNRs resulted in a reduction in both parameters, indicative of increased membrane fluidity and cytoskeletal rearrangement. These findings provide new insights into the biomechanical effects of GNRs on macrophages and may enlighten the design of future phototherapeutic approaches.