Solid-Phase Fluorescence Filter Effect: Toward Field and Ultrasensitive Detection of Iodine Speciation in Seawater

On-site analysis of iodine and its speciation in seawater is important for the prediction of radioactive iodine contamination. However, current methods, both colorimetric and instrumental, cannot meet the recent demand for field analysis and an increased reliability of results. Herein, a solid-phase fluorescence filter effect (SPFFE) induced by iodine was found and further used to develop a ratiometric fluorescence paper analysis device (RFPAD) for the analysis of iodine and its speciation in seawater. The proposed SPFFE-based assay surpasses the sensitivity and interference limitations arising from a specific extinction coefficient and multiple absorbers during real sample analysis, yielding an ultralow limit of detection of 550 pM for iodine. In conjunction with a smartphone, a developed program, and a sensing platform, both field-sensitive detection and speciation analysis of iodine could be achieved. An RFPAD was successfully used for the field speciation analysis of iodine and iodate in the South China Sea, showing excellent anti-interference capability and retaining promising potential for warning about radioactive iodine contamination in the ocean.