Vapor I-Mediated Robust Aggregation/Etching of Silver Nanoparticles for Sensitive and On-Site SERS Monitoring of Iodine in Seawater.

While oceanic iodine plays a critical role in monitoring marine pollution and biogeochemical cycles, existing detection methods suffer from compromised sensitivity, laborious pretreatment, and field-incompatible operation. Herein, we present a vapor-phase molecular recognition strategy that leverages iodine (I)-induced structural transformation of silver nanoparticles (AgNPs) for surface-enhanced Raman scattering (SERS) indirect detection, with rhodamine 6G (Rh6G) as a Raman probe of seawater iodine. Spectroscopic and electron microscopic results showed that I induced stronger sequential aggregation and anisotropic etching of nanoparticles than I, effectively suppressing SERS enhancement. Theoretical calculations reveal that I exhibits a 3-fold stronger binding affinity with AgNPs compared to I. By integrating headspace sampling with paper-based SERS substrates, this method achieves matrix interference elimination through gas-solid phase separation while enhancing sensitivity via vapor preconcentration. The developed approach demonstrates a low detection limit of 15.1 nM for iodide (RSD = 5.0%, = 15), with a linear response across 50-1000 nM, and no significant interference with coexisting anions at 1000-fold higher concentrations. Field deployment along the Southeast China Sea coastline showed excellent correlation with standard mass spectrometry measurements. This work not only elucidates the molecular-level interaction between I and noble metal nanostructures but also establishes a new paradigm for in-field detection of marine radioactive isotopes through vapor-phase reaction engineering.