Real-Time Single-Particle Tracking of Intracellular pH Dynamics during Ferroptosis Using Plasmonic Core–Satellite Nanostructures

Ferroptosis, an iron-dependent regulated cell death process, is characterized by lysosomal membrane permeabilization and pH dysregulation. Here, we report a DNA-programmed plasmonic nanoprobe based on i-motif-mediated gold core–satellite nanostructures (Au CSNSs) for single-particle resolution mapping of intracellular pH dynamics during ferroptosis. The i-motif DNA linker undergoes pH-dependent conformational switching, dynamically tuning the interparticle gap between 45 nm gold core nanoparticles (Au core NPs) and 15 nm gold satellite nanoparticles (Au satellite NPs). This architecture achieves a large localized surface plasmon resonance (LSPR) shift in the pH range of 5.6–6.8, enabling reversible and linear pH sensing (R² = 0.97) with excellent photostability. During ferroptosis induced by exogenous iron, Au CSNSs displayed rapid spectral shifts corresponding to lysosomal H⁺ leakage, corroborated by acridine orange staining. Notably, mitophagy activation via rapamycin pretreatment sensitized cells to low-dose iron (1 μM), triggering earlier and more pronounced pH changes. This work establishes a novel platform for investigating pH-dependent signaling in ferroptosis, with implications for understanding mitochondria–lysosome crosstalk and developing targeted cancer therapies.