Zn(II) ion modulated red emitting copper nanocluster probe for the fluorescence turn on sensing of RDX

Field employed detection of hidden explosives has drawn intense attention as it poses significant threat to public safety and security. Among the explosives, the selective detection of heterocyclic nitramine compounds such as 1,3,5-trinitrotriazine (RDX) is still challenging since it lacks nitroaromatic rings, possess higher LUMO energies and even lower vapour pressure. In the present work, water soluble BSA stabilized copper nanocluster is synthesized by using sodium borohydride as reducing agent. The resultant nanocluster having size less than 3 nm showed intense red emission at 650 nm upon excitation at 440 nm. Fluorescence of the BSA stabilized copper nanocluster is effectively quenched by the addition of Zn(II) ion and the quenching is attributed to photoinduced electron transfer followed by aggregation. The limit of detection for Zn(II) ion is obtained as 15 nM and is much lower than that of the World Health organization permitted level of Zn(II) ion in drinking water which is 76 mu M. The fast recovery of the fluorescence is observed after addition of RDX to the quenched system which is attributed to the high affinity of Zn(II) ion with RDX. The limit of detection for RDX sensing is obtained at 1.62 nM. Additionally, a straight forward fluorescent paper strip sensor is developed to detect both Zn(II) and RDX, providing an onsite detecting platform for both homeland and environmental security.