Extremely Small Iron Oxide Nanoparticles with pH-Dependent Solubility Transition as T₁/T₂ Switchable Contrast Agents for MRI

Extremely small iron oxide nanoparticles (ESIONPs), which have a switchable contrast signal and favorable biocompatibility, are gaining considerable attention as smart magnetic resonance imaging (MRI) agents (CAs). Adaptive MRI CAs could improve the accuracy of tumor diagnosis because they realize rapid conversion under an endogenous stimulus. Herein, based on hydrophilic to hydrophobic transition polymers, we propose pH-responsive T1/T2 ESIONP agent. ESIONPs functionalized at surface with adamantane groups through polyethylene glycol (PEG) chain, subsequently, stimuli-responsive polymer (PSDM) pH-dependent solubility is introduced host–guest interaction between β-cyclodextrin (β-CD). The obtained ESIONPs-PEG-PSDM equipped remarkable pH responsiveness, triggers aggregation acid condition, leading switch from T1 T2 In vivo experiments show that selectively enhanced location after injection ESIONPs-PEG-PSDM. Therefore, pH-induced potential agent for precise diagnosis.