Switchable and biodegradable nanostructures for safe and precise tumor diagnostics

stability, activation responsiveness and degradation kinetics. This tutorial review provides a mechanistic and translational overview of switchable and biodegradable nanostructures for cancer diagnostics, with an emphasis on current design strategies in the context of preclinical performance and translational constraints. We discuss how the physical principles of major imaging modalities guide specific design requirements and synthesize how key physicochemical parameters govern the balance between pharmacokinetics, activation, and degradation/clearance kinetics. Finally, we highlight emerging OFF-ON designs, including cascade amplification and logic-gated strategies, and discuss unresolved challenges in achieving consistent activation performance, sufficient stability and predictable clearance across different imaging scales, including single-cell and whole-body levels.