Abstract

The integrity and function of biological membranes are fundamentally linked to the electrostatic potential at the lipid-water interface, which governs the adsorption and activity of charged molecules. This study investigates the complex interplay between the fluorescent probe Pyranine (8-hydroxypyrene-1,3,6-trisulfonic acid, HPTS) and Bilayer Lipid Membranes (BLMs), focusing on the changes in surface potential induced by its adsorption and subsequent photochemical reactions. Using a specialized potentiometric technique, we measured the electrostatic potential at the membrane-water interface in real-time as Pyranine adsorbed onto the BLM surface. Our findings reveal that Pyranine adsorption significantly alters the membrane's surface charge, demonstrating a strong dependence on pH and ionic strength. Furthermore, light-induced photochemical reactions of the adsorbed Pyranine lead to a transient, measurable change in the electrostatic potential, suggesting a mechanism involving proton release or charge separation at the interface. These results provide critical insights into the physical chemistry of membrane-probe interactions and the use of Pyranine as a dynamic reporter of local electric fields, which is vital for understanding energy transduction and signaling processes in cell biology.