Fluorescent Nanodiamond/Au@PDA Nanoparticle Composites as Fluorescent Sensors for the Detection of miRNA-21

Fluorescent nanodiamonds (FNDs) containing nitrogen vacancies (NVs) are a susceptible and multifunctional quantum sensor. FNDs have been used for temperature and magnetic field sensing at the nanometer level. The regulation of the quantum spin properties of NV centers using nanomaterials is a critical factor in the adequate preparation of quantum sensors. Herein, Au@PDA nanoparticles were prepared by coating a layer of polydopamine (PDA) on the surface of Au nanoparticles via a self-polymerization reaction. Au@PDA acts as a nanoheater to precisely control the quantum spin characteristics of the NV center. In the presence of Au@PDA, the fluorescence intensity, fluorescence lifetime, and relaxation time of the NV center decrease by 46.72, 70.87, and 64.02%, respectively. At a near-infrared laser power of 2.2 mW, compared with FNDs, the splitting value D of the optical detection magnetic resonance (ODMR) spectrum of the NV center of FND-Au@PDA increases by 3.35 MHz, and the temperature △T of FND increases by 44.01 K. Moreover, results show that FND-Au@PDA retains the quantum spin characteristics of the NV center and that a magnetic field can increase the relaxation time of the NV center. Furthermore, the miRNA-21 concentration detection limit of the FND-Au@PDA quantum sensor is 5.4 × 10–17 mol/L. Our findings indicate that FND-Au@PDA acts as a multifunctional quantum sensor in biological systems. This study provides an idea and an experimental basis for preparing and applying NV center quantum sensors.