Nanoscale Terahertz Monitoring on Multiphase Dynamic Assembly of Nanoparticles under Aqueous Environment

Probing the kinetic evolution of nanoparticle (NP) growth in liquids is essential for understanding complex nano‐phases and their corresponding functions. Terahertz (THz) sensing, an emerging technology for next‐generation laser photonics, has been developed with unique photonic features, including label‐free, non‐destructive, and molecular‐specific spectral characteristics. Recently, metasurface‐based sensing platforms have helped trace biomolecules by overcoming low THz absorption cross‐sectional limits. However, the direct probing of THz signals in aqueous environments remains difficult. Here, the authors report that vertically aligned nanogap‐hybridized metasurfaces can efficiently trap traveling NPs in the sensing region, thus enabling us to monitor the real‐time kinetic evolution of NP assemblies in liquids. The THz photonics approach, together with an electric tweezing technique via spatially matching optical hotspots to particle trapping sites with a nanoscale spatial resolution, is highly promising for underwater THz analysis, forging a route toward unraveling the physicochemical events of nature within an ultra‐broadband wavelength regime.