  Fluorescent nanodiamonds (fNDs) containing Nitrogen Vacancy (NV) centres are
promising candidates for quantum sensing in biological environments. However,
to date, there has been little progress made to combine the sensing
capabilities of fNDs with biomimetic substrates used in the laboratory to
support physiologically representative cell behaviour. This work describes the
fabrication and implementation of electrospun Poly Lactic-co-Glycolic Acid
(PLGA) nanofibers embedded with fNDs for optical quantum sensing in an
environment, which recapitulates the nanoscale architecture and topography of
the cell niche. A range of solutions for electrospinning was prepared by mixing
fNDs in different combinations of PLGA and it was shown that fND distribution
was highly dependent on PLGA and solvent concentrations. The formulation that
produced uniformly dispersed fNDs was identified and subsequently electrospun
into nanofibers. The resulting fND nanofibers were characterised using
fluorescent microscopy and Scanning Electron Microscopy (SEM). Quantum
measurements were also performed via optically detected magnetic resonance
(ODMR) and longitudinal spin relaxometry. Time varying magnetic fields external
to the fND nanofibers were detected using continuous wave ODMR to demonstrate
the sensing capability of the embedded fNDs. The potential utility of fND
embedded nanofibers for use as biosensors in physiological environments was
demonstrated by their ability to support highly viable populations of
differentiated neural stem cells, a major therapeutic population able to
produce electrically active neuronal circuits. The successful acquisition of
ODMR spectra from the fNDs in the presence of live cells was also demonstrated
on cultures of differentiating neural stem cells.
