A nano-structured reporter for high-sensitivity contaminant detection in groundwater

Groundwater remediation is vital for meeting the ever-growing demand for clean water. However, accurately delineating subsurface contamination by free-phase organic contaminants (FPOCs) remains a major remediation hurdle. Here, we design a nano-structured reporter featuring a hydrophobic contaminant probe embedded within the framework of polyvinyl alcohol (PVA)-grafted carboxylated carbon black, for ultrahigh-sensitivity FPOC detection. When injected into the subsurface, the reporter moves with groundwater as the PVA chains prevent nanoparticle aggregation and deposition. The presence of even FPOC traces (as thin films or small droplets) triggers the release of probe molecules, enabled by the super-responsive coiling of PVA chains at organic-water interfaces. Contaminant mass is directly proportional to the amount of probe partitioning into the FPOCs, which can be accurately determined by fitting transport data with a two-site transport model. We offer proof-of-concept that this approach overcomes hydrogeological and FPOC distribution complexities that hinder conventional characterization of contaminant source zones.