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