  Benefitting from the excellent characteristics such as low cytotoxicity,
functionalization versatility, and tunable fluorescence, nanodiamonds (NDs)
have shown enormous application potentials in the biomedical field. Herein, we
proposed, for the first time to our best knowledge, to integrate NDs on a
plasmonic interface constructed on a side-polished fiber using drop-casting
method. The added NDs engineers the plasmonic interface towards improving the
sensing field, thus enhancing the sensitivity, which, moreover, is
significantly dependent on the number of drop-casting cycles (DCs) and the used
concentration of NDs dispersion solution. Experimental results suggest that
properly increasing the NDs dispersion concentration is beneficial to obtain a
higher sensitivity while using a fewer number of DCs, but the excessive
concentration extremely deteriorates the resonance dip. Experimentally, using
the optimal 0.2 mg/mL concentration and 3 DCs, we achieve the highest RI
sensitivity of 3582 nm/RIU, which shows an enhancement of 73.8% compared to the
case without NDs modification. The sensitivity enhancement in biosensing is
also proved by employing bovine serum albumin as a demo. The behind mechanism
is explored via characterizations and simulations. This work opens up a new
application form for NDs, i.e. integrating NDs with a plasmonic interface
towards high-performance biosensing.
