Processing-Defined Nanodiamonds: Material-State Control for Reliable Function

Nanodiamonds have attracted increasing interest owing to their unique optical, spin, thermal and chemical properties, enabling emerging applications in quantum technologies, biomedical diagnostics, thermal management and electrochemical sensing. However, the reported performance of nanodiamonds varies considerably among studies because synthesis routes, purification processes, defect populations, surface chemistry and interfacial structures generate distinct material states. A processing-defined material-state perspective is proposed to understand how these coupled characteristics determine functional properties and application performance. This perspective highlights that nanodiamond functionality is not governed by isolated parameters, but by the coupled evolution of defects, surfaces and interfaces during processing. Representative applications demonstrate that different functions require distinct material-state configurations, involving trade-offs among spin coherence, fluorescence stability, interfacial heat transfer and charge-transfer behaviour. Achieving reliable nanodiamond technologies therefore requires application-oriented optimization, standardized material-state reporting and reproducible processing strategies. This framework provides a pathway toward rational design and scalable integration of nanodiamonds for advanced functional applications.