Synthesis and Quantum Metrology of Metal–Organic Framework-Coated Nanodiamonds Containing Nitrogen Vacancy Centers

Fluorescent nanodiamonds (NDs) containing nitrogen vacancy centers (NV) have promising applications in quantum sensing, quantum computing, catalytic, and imaging applications. Functionalization of NDs with an ordered, porous coating can provide well-defined sites for ND immobilization and analyte interaction with the ND surface, furnishing a tunable environment for quantum applications and catalysis. Here, a facile strategy for functionalizing NV NDs with the biocompatible zeolitic imidazole framework-8 (ZIF-8) metal–organic framework (MOF) is demonstrated. The composites were structurally characterized by electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy, indicating the formation of well-dispersed ND three-dimensional structures supported by a MOF matrix. Crucially, the fluorescence and optically detected magnetic resonance properties were preserved following ZIF-8 encapsulation, while spin relaxometry studies indicate that MOF functionalization lengthens the spin longitudinal relaxation time T₁, a critical quantum parameter for sensing applications. We further demonstrate that the average number of NDs per MOF can be controlled by increasing the concentration of NDs used in the synthesis. The tunable design of NDs@MOF materials has important implications for quantum sensing, quantum computing, and related applications, and the synthetic strategy and optical characterization data presented here provide a foundation for future exploration of ND@MOF systems.