Neutron Reflectometry of Soft Films Supported on Electrified Surfaces

Abstract

The specular reflection of neutrons is a non-destructive, nuclear-based technique, sensitive to low atomic number elements, has a high penetration depth, and can distinguish between isotopes of the same element. This makes neutron reflectometry (NR) especially effective for the study of biological membranes, soft films and buried interfaces. Furthermore, commonly used NRsubstrates such as silicon and quartz single-crystals can be modified with thin metallic layers to form conductive supports allowing for the precise control of the electrical state of the interface. The coupling of NR with in-situ electrochemical control provides a powerful tool to study the composition of soft and/or buried interfaces under conditions that mimic, for example,transmembrane potentials or corrosion potentials.Here we report our recent efforts to perform in situ electrochemical NR studies and the previous experimental framework from which they were developed. The talk will address technical and infrastructure challenges but emphasize scientific highlights from our work with biomimeticphospholipid membranes. 'Isotopic variation has been applied to quantify the electroporation and distribution of water as a function of surface charge density in lipid bilayers. These studies have more recently been extended to study the location of redox-active ubiquinone (coenzyme Q10) in biomimetic lipid bilayers as a function of potential and temperature. To probe the location of ubiquinone, a phospholipid bilayer was prepared on a gold coated solid substrate using a combination of Langmuir-Blodgett and vesicle fusion techniques. The combination of these two methods allowed for the composition of the inner and outer membrane leaflets to be varied. Preliminary results show sensitivity to the location of a small biologically relevant molecule.