Uncovering the Lipid Interface in Neurotransmission: Single Molecule Measurements of Neurotransmitters Interacting with Membranes Reveal Species Dependent Membrane Binding

Neurotransmitters (NTs) have traditionally been understood to act via aqueous-phase receptor binding, but growing evidence suggests the lipid bilayer plays an active role in modulating their signalling. Here, single-molecule measurements are presented using whispering gallery mode (WGM) optical sensors to directly observe NT interactions with supported lipid bilayers. Aromatic NTs, such as histamine, dopamine, epinephrine, and L-norepinephrine, exhibit stable, step-like resonance shifts, indicating sustained membrane association, while amino acid-like NTs generate only transient interactions. Kinetic analyses of spike and step events reveal species-dependent association and dissociation rates. Complementary Langmuir trough experiments confirm membrane partitioning by the NT histamine, but not by glycine. These findings support a model of selective membrane partitioning in neurotransmission and highlight the bilayer as an active participant in NT signalling. This work advances the understanding of NT-membrane interactions and provides a platform for probing non-canonical modes of synaptic communication.