  Owing to the unique electronic spin properties, the nitrogen-vacancy (NV)
centers hosted in diamond have emerged as a powerful quantum sensor for various
physical parameters and biological species. In this work, a miniature
optical-fiber quantum probe, configured by chemically-modifying nanodiamonds NV
centers on the surface of a cone fiber tip, is developed. Based on
continue-wave optically detected magnetic resonance method and lock-in
amplifying technique, it is found that the sensing performance of the probe can
be engineered by varying the nanodiamonds dispersion concentration and
modification duration in the chemical modification process. Combined with a
pair of magnetic flux concentrators, the magnetic field detection sensitivity
of the probe is significantly enhanced to 0.57 nT/Hz1/2 @ 1Hz, a new record
among the fiber magnetometers based on nanodiamonds NV. Taking Gd3+ as the
demo, the capability of the probe in paramagnetic species detection is also
demonstrated experimentally. Our work provides a new approach to develop NV
center as quantum probe featuring high integration, miniature size,
multifunction, and high sensitivity, etc.
