Real-Time Tracking of Ion Migration Process at the Single-Nanoparticle Level

The ion migration behavior in nanomaterials is closely related to their photophysical properties. Real-time monitoring of ion migration process within individual nanoparticles is of great significance, but which faces a great challenge. Herein, in situ visualization of ion migration at the single-nanoparticle level is achieved using a powerful dark-field microscopy (DFM) platform. Specifically, silver (Ag⁺) ions, owing to their strong binding affinity with selenium and favorable Coulomb interaction, can permeate into selenium nanoparticles (SeNPs), triggering a phase transformation from trigonal selenium (t-Se) to cubic Ag₂Se. This transition leads to a distinct shift in scattered light from green to red due to the reduction of optical band gap, allowing real-time optical tracking of the ion migration behavior. The transformation of SeNPs into Ag₂Se enables a dual-purpose system: it functions not only as a sensitive probe for Ag⁺ detection but also generates a potent photothermal nanoreagent, demonstrating significant potential for cancer theranostics. This work not only provides direct visual insight into the dynamic photophysical processes underlying crystal phase transformation, but also establishes a general strategy for tracking ion migration process, facilitating the rational design and application of advanced functional nanomaterials.