Ultrasensitive optical detection of strontium ions by specific nanosensor with ultrahigh binding affinity

The release and escape of radioactive materials has posed tremendous threats to the global environment. Among various radioactive elements, ⁹⁰Sr has attracted growing attention due to its long half-life and its tendency to accumulate in bone tissue. Nonetheless, the concentration of ⁹⁰Sr in radioactive waste is exceedingly low, far below the detection limits of currently available strontium-targeting chemical sensors. Herein, we propose an optical nanosensor (Sr²⁺-nanosensor) that exhibits an ultra-low detection limit of 0.5 nM, surpassing the ⁹⁰Sr in the treated radioactive water from the Fukushima. The sensor offers wide sensing range of eight orders of magnitude, rapid response of less than 10 s, and high selectivity against 31 common ions. These excellent performances are attributed to a specific ligand (Sr²⁺-ligand) for Sr²⁺ recognition. The Sr²⁺ is found to be bound by six oxygen atoms from the Sr²⁺-ligand with a stability constant at least two orders higher than that of other traditional ligands. This study offers invaluable insights for the design of Sr²⁺-sensing methodologies as well as a technique for detecting trace amounts of environmental radioactive pollution.