  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.
