Retention of lead sensitized terbium dopant emission in zinc sulfide nanoparticles in presence of co-existent metal ions: Detection of lead ion in aqueous media with nanomolar concentration by a facile post-synthetic reaction under pre-cation exchange condition

Suitable co-dopant(s) can electronically interact to tune the emission of inorganic nanoparticles (NPs). Such a case can be realized where post-synthetically added co-dopant Pb²⁺ act as a co-sensitizer (in addition to the NP’s sensitization effect) for Tb³⁺ emission in the terbium cation doped zinc sulfide [Zn(Tb)S] NPs in the pre-cation exchange reaction regimes under ambient conditions. This work evaluates possible practical utilization of this co-sensitization by this facile synthetic strategy for Pb²⁺ detection in aqueous media in presence of co-existent Mⁿ⁺ [Na⁺, K⁺, Mg²⁺, Ca²⁺, Cd²⁺, and Hg²⁺]. The Pb²⁺ induced Tb³⁺ emission enhancement is retained irrespective of these Mⁿ⁺ introduction in the media, with key mechanistic steps unperturbed. These outcomes ideally place using the Zn(Tb)S NPs to detect Pb²⁺ in aqueous media. A limit of detection (LOD) and limit of quantification (LOQ) for Pb²⁺ is estimated to be 3 ppb (15 nM) and 10 ppb (50 nM) from the pre-cation exchange conditions. The use of discussed strategy is verified using quantitatively contaminated drinking water and tap water by a spike recovery experiment. This provides a remarkable superiority by at least 2 orders of magnitude to detect Pb²⁺, over an alternate strategy using the cation exchange reaction conditions resulting from formation of lower band gap Pb(Tb)S NPs. The strategy presented unequivocally establishes that the rich light induced processes in the pre-cation exchange reaction conditions in the quantum dots can remarkably improve the Pb²⁺ detection by virtue of accessing lower concentrations.