Herein we developed a method for observation and analysis of lipid wrapping around nanoparticles with electron paramagnetic resonance (EPR). It was used for analysis of lipid wrapping around titanium dioxide and carbon nanotubes. For acquisition of EPR spectra, this method requires labeling of lipid wraps with spin-labeling molecules. We used six different spin-labeling molecules and determined their usefulness for lipid wrapping observation. With computational analysis of the spectra, we determined motional patterns of lipids in the samples and strength of molecular ordering at the interface between nanoparticles and lipid bilayers. We used conformational entropy to compare complex results of computational analysis of the spectra.
We found out that success of detection of lipid ordering on nanomaterial surface is determined by surface type and chemical structure of spin labels. In case of hydrophilic surface of titanium dioxide nanotubes, lipid ordering was only observed for spin label GluSL Stearate. Molecular proximity between nanomaterial and spin labels for this labeling molecule is enabled by the molecule’s chemical structure. In case of hydrophobic surface of carbon nanotubes, all of the spin labels used in the experiments observed lipid ordering. The degree of detected ordering was found out to be dependent on position of nitroxide group, size of spin-labeled molecules and other functional groups attached to the spin labels.
Increasing use of nanomaterials in everyday life has led to increased exposure of living organisms to nanoparticles. Their effects on environment and health is mostly unknown or poorly understood. Relationship between properties of nanoparticles and their harmfulness is not well-known since the mechanisms that lead to harmfulness are not understood. Lipid wrapping around nanoparticles is one of the phenomena that can be observed at contact between nanoparticles and biological membranes. Understanding of lipid wrapping could lead to improved predictability of nanomaterial’s toxicity. Results in this work show that EPR spectroscopy is a suitable tool for analysis of lipid wraps around nanoparticles. The developed method could become a way of determining harmfulness of nanomaterials.