All-fiber quantum relaxometry for biochemical sensing based on diamond NV centers

The longitudinal relaxation time (termed as T ) of nitrogen-vacancy (NV) centers in nanodiamonds can be affected by surface electric or magnetic noise, which has been exploited to develop cutting-edge quantum relaxometry for biochemical sensing. In this work, a tiny all-fiber quantum probe based on longitudinal relaxometry was developed by chemically-anchoring nanodiamonds on the surface of a cone fiber tip. The dependences of T on surface electric and magnetic noise were discussed in theories first and then experimentally demonstrated in varied pH and Gd concentration solutions, respectively. Because of NV centers being subject to enhanced coupling from surface noise, T reduced from 290 to 245 µs when pH changed from 3 to 9 and reduced to 220 µs when Gd concentration increased to 10 mM, agreeing well with theoretical results. Based on these, the Gd -tagged-biotin and streptavidin model was designed and implemented on the all-fiber probe, and results demonstrated the detection of biotin with a limit of 168 nM and good specificity. This paper opens a new way to develop an all-fiber quantum probe by exploiting the unique electrical spin properties of NV centers, and the probe shows great potential for biological detection with high sensitivity and specificity.