“We describe the kinetics of the formation mechanism of lipid bilayers on vertically oriented silicon nanowires and compare them with planar silica surfaces. Using surface-sensitive and time-dependent fluorescence microscopy, we observed how the process is accelerated due to the energetically favoured expansion of the membrane along the nanowires due to their high aspect ratio. Aided by light guiding and signal enhancement properties of the nanowires, we achieved single-molecule resolution and a higher signal-to-noise ratio in our measurements,” says Julia Valderas, a PhD student at NanoLund.
The role of nanowires as a support for the formation of model lipid membranes, and their potential to study membrane-membrane interactions is central to the study.
Nanowires excellent for studying membrane systems
“We have studied the formation of artificially supported lipid bilayers (SLBs) on nanowires of high curvature and compared it to planar silica. Using the light-guiding and fluorescence signal enhancement properties of the nanowires, we can monitor in real-time the formation of the membranes while detecting single-molecule events using conventional epifluorescence microscopy setup. These findings give new insights into the mechanisms of SLB formation on substrates of high curvature as membrane models for studying the cell,” says Julia Valderas.
The results, she states, are interesting because the artificial model membranes are used to mimic and study the cell membrane.
“They are often formed on planar supports, by the adsorption and fusion of lipid vesicles (spherical arrangement of lipids). Here, we present the use of nanowire arrays to study the formation of the SLB on substrates of higher curvature. It has been reported previously that the formation of the SLB on curved substrates is often hindered, but the unique dimensions and optical properties of the nanowires make them an excellent choice for studying membrane systems.
What is the most important thing you have learned from this study?
“For the first time, we have proposed a model that explains the process of SLB’s formation on nanowires, which is energetically favored and accelerated as a consequence of their high-aspect ratio. Single-vesicle adsorption and fusion events can be detected, and when the SLB is formed, the dynamics and diffusivity of individual fluorescent molecules can also be monitored.”
These results could be used to study the diffusivity of lipids and other dynamic phenomena in membranes.
The results may be useful once researchers have optimized and described the SLB formation process on nanowires.
“We believe that they have a huge potential as platforms for the study of membranes and their interactions. Combining their curvature and optical properties, we could study membrane-membrane interactions, observe and detect single molecules at very small concentrations, or replicate interesting cellular phenomena,” says Julia Valderas.
How may the study be important to the public?
“For nano and biomedical applications, there is an increasing interest in lipid nanoparticle systems for the delivery of ARN-based therapeutics such as COVID vaccines, for example. To improve their efficiency, it is crucial to understand how lipid nanoparticles enter the cell and interact with the membrane. Thus, we envision our SLB nanowires systems as the perfect platform to model and study these interactions in vitro and with high sensitivity,” says Julia Valderas.
Was there something in the results that took you by surprise?
“Although it was not the original focus of the study, we discovered that, once a homogeneous and mobile SLB is formed on the nanowires, it is possible to detect the fluctuations of individual lipids moving on and off the nanowires with a high signal-to-noise ratio. These results could be used to study the diffusivity of lipids and other dynamic phenomena in membranes.”