Singlet Oxygen-Mediated Lipid Nanotube Extrusion from Supported Lipid Membranes

Herein, we report the photoinduced deformation of unsaturated supported lipid bilayers (SLBs), leading to the formation of lipid nanotubes that extrude away from the surface up to tens of micrometers in length. These nanotubes subsequently fuse and/or collapse into disk-like structures. These observations were made while seeking to examine the optical and electrochemical stability, as well as the potential toxicity, of conjugated structures with alternating electron-donating and electron-accepting fragments (ADA). Mechanistic studies, including irradiation in the presence and absence of oxygen, addition of a singlet oxygen quencher, and incorporation of ADA oligomers into phospholipid membranes bearing either saturated or monounsaturated fatty acids, consistently pointed to a mechanism invoking ADA photosensitized singlet oxygen-mediated lipid peroxidation via the ene reaction. Importantly, membrane deformation occurs only above a critical threshold of singlet oxygen flux rather than above a critical dose of this reactive species, indicating that the driving force for nanotube formation arises from the rapid expansion of unsaturated lipid molecules following the ene reaction on an otherwise laterally incompressible membrane. Chemical and physical insights into the driving forces steering membrane deformation and lipid nanotube formation and collapse are discussed herein. These findings highlight the opportunity of sculpting and engineering biointerfaces by exploiting the mechanical mismatch between the hard and soft material through the photoinduced generation of localized interfacial stress.