[en] Highlights: • Asymmetricplasmonic structures with dual functionalities of water purification and pollution detection is formed by a self-assembly process. • The dark porousside of the APS can enable efficient solar steam generation (with energy transfer efficiency ~ 80%). • The shiny metallic side can enable sensitive chemicals detection (with detection limit down to ~ 10–12M). • This dual functional APS can enable on-site pollution detection and purification of water, with long time durable performance up to ~ 45 days. In the past decade, various rational designed plasmonic structures have demonstrated extraordinary functionalities from information, photothermal therapy to solar energy conversion. Recently, plasmon enhanced solar steam generation is attracting a lot of attention for its great potential in desalination, sterilization, etc. Here for the first time we demonstrate an asymmetric plasmonic structure (APS) formed by self-assembly of close packed silver nanoparticles into porous templates with dual functions, solar water purification and pollution detection. The dark porous side of the APS can enable efficient solar steam generation (with energy transfer efficiency ~ 80%) while the shiny metallic side can enable sensitive chemicals detection (with detection limit down to ~ 10^–12 M). Such impressive performance in solar thermal conversion and chemical sensing are stemmed from the broadband and efficient light absorption (solar absorptivity > 90%) as well as pronounced local field enhancement (maximal enhancement factor ~ 10⁹), respectively. As an example of functional integration, this dual functional APS can enable on-site pollution detection and purification of water: water sources contaminated with various kinds of common pollutants have been examined and purified. Both functions of detection and purification exhibit long time durable performance up to ~ 45 days, with < 20% decay in Raman intensity and < 10% decay in energy transfer efficiency, respectively.