Label-free phase change detection of lipid bilayers using nanoscale diamond magnetometry

TL;DR

This paper demonstrates a label-free method using nanoscale diamond magnetometry to detect phase changes in lipid bilayers by analyzing nanoscale NMR signals and molecular diffusion, revealing temperature-dependent dynamics.

Contribution

It introduces a novel application of NV center-based magnetometry for nanoscale, label-free phase change detection in lipid bilayers, combining experimental and simulation approaches.

Findings

Lipid bilayer thickness confirmed to be 6.2 nm ± 3.4 nm.

Diffusion constant increases from 1.5 to 3.0 nm²/μs with temperature.

Nanoscale NMR signals reveal phase and temperature-dependent membrane dynamics.

Abstract

The NV center in a diamond is a quantum sensor with exceptional quality for highly sensitive nanoscale analysis of NMR spectra and thermometry. In this study, we investigate nanoscale phase change detection of lipid bilayers utilizing ensemble-averaged nuclear spin detection from small volume ~ (6 nm)$^{3}$, which was determined by the depth of the NV center. Analysis of nanoscale NMR signal confirm thickness of lipid bilayer to be 6.2 nm $\pm$ 3.4 nm with proton density of 65 proton/nm$^{3}$ verifying formation of lipid bilayer on top of diamond sample. Correlation spectroscopy from nanoscale volume reveals quantum oscillation at 3.06 MHz corresponding to the Larmor frequency of proton at an applied magnetic field of 71.8 mT. The result of the correlation spectroscopy was compared with the 2D molecular diffusion model constructed by Monte Carlo simulation combined with results from molecular dynamics simulation. There is a change in diffusion constant from 1.5 $\pm$ 0.25 nm$^{2}$/${\mu}$s to 3.0 $\pm$ 0.5 nm$^{2}$/${\mu}$s when the temperature changes from 26.5 $^\circ$C to 36.0 $^\circ$C. Our results demonstrate that simultaneous observation of changes in translational diffusion and temperature is possible in label-free measurements using nanoscale diamond magnetometry. Our method paves the way for label-free imaging of cell membranes for understanding its phase composition and dynamics.