Fluorescence intensity and lifetime imaging of a viscosity sensitive zwitterionic amphiphile for cell membrane tension and apoptosis bodies

The intricate biophysical properties of the cell membrane, encompassing polarity, hydration status, viscosity, lipid order, and electrostatics, can be meticulously monitored and analyzed utilizing sophisticated environment-sensitive membrane probes. Among these probes, viscosity-sensitive variants stand out for their ability to alter emission intensity and fluorescence lifetime in densely packed lipid environments, restricting their rotational freedom. However, there is a lack of tools in resisting endocytosis by selective intramolecular interaction and establishing a more quantifiable relationship between viscosity and their fluorescent nature. In this work, we introduce MNA, an innovative amphiphilic fluorescent probe featuring a zwitterionic headgroup. MNA's exceptional affinity for membranes is reinforced by its ability to interact with phospholipid molecules in three distinct ways, encompassing both the zwitterionic head and hydrophobic tail. Governed by the hemicyanine-naphthalimide planarization process, MNA's fluorescence intensity and lifetime exhibit a remarkable sensitivity to microviscosity, empowering it to illuminate membrane organizations and dynamics, including membrane tension. Notably, both the fluorescence intensity and lifetime of MNA can be elegantly modeled using a logarithmic function. During critical cellular processes such as phagocytosis and apoptosis, MNA captures the dynamic fluctuations of membrane tension with high sensitivity using fluorescence lifetime microscopy, offering a unique perspective on membrane behavior. As a powerful tool, MNA provides profound insights into membrane tension and reorganization in response to various stimuli, facilitating novel discoveries in cellular biology and biomedical research.