Amine-Capped ZnS−Mn²⁺ Nanocrystals for Fluorescence Detection of Trace TNT Explosive

TLDR

Organic amine‑capped ZnS nanocrystals bind TNT species through acid–base interactions between electron‑rich amino ligands and electron‑deficient aromatic rings. Binding of TNT anions to the amino monolayer quenches Mn²⁺ photoluminescence via electron transfer from the ZnS conduction band to the TNT LUMO. These amine‑capped Mn²⁺‑doped ZnS nanocrystals detect ultratrace TNT down to 1 nM in solution or parts‑per‑billion vapor, with 2–5‑fold amplified quenching constants, high quantum yield, stability, and the ability to distinguish nitroaromatic analytes.

Abstract

Mn2+-doped ZnS nanocrystals with an amine-capping layer have been synthesized and used for the fluorescence detection of ultratrace 2,4,6-trinitrotoluene (TNT) by quenching the strong orange Mn2+ photoluminescence. The organic amine-capped nanocrystals can bind TNT species from solution and atmosphere by the acid−base pairing interaction between electron-rich amino ligands and electron-deficient aromatic rings. The resultant TNT anions bound onto the amino monolayer can efficiently quench the Mn2+ photoluminescence through the electron transfer from the conductive band of ZnS to the lowest unoccupied molecular orbital (LUMO) of TNT anions. The amino ligands provide an amplified response to the binding events of nitroaromatic compounds by the 2- to ∼5-fold increase in quenching constants. Moreover, a large difference in quenching efficiency was observed for different types of nitroaromatic analytes, dependent on the affinity of nitro analytes to the amino monolayer and their electron-accepting abilities. The amine-capped nanocrystals can sensitively detect down to 1 nM TNT in solution or several parts-per-billion of TNT vapor in atmosphere. The ion-doped nanocrystal sensors reported here show a remarkable air/solution stability, high quantum yield, and strong analyte affinity and, therefore, are well-suited for detecting the ultratrace TNT and distinguishing different nitro compounds.