A Luminescent Nanocrystal Marker for the Selective and Ultrasensitive Detection of Explosives

We developed a luminescent probe for the selective and sensitive detection of an explosive, i.e., picric acid (PA), based on the luminescence quenching of Ce^III and Tb^III co-doped Sr₂GdF₇ nanocrystals. A new colloidal synthesis route at low temperature (80 °C) was developed to synthesize the luminescent nanocrystals host matrix Sr₂GdF₇. The nanocrystals showed strong green emission under UV excitation (290 nm) by efficient energy transfer from Ce^III to Tb^III ions. The functionalization of the nanocrystals with l-cysteine (Cys) rendered the luminescent probe water dispersible. The presence of the −NH₂ groups of Cys allowed the selective interaction of the probe with PA among other nitro explosives. This caused a 92 % reduction of the photoluminescence intensity of Tb^III in the Sr₂GdF₇ nanocrystals, and led to the selective detection of PA with an unprecedented limit of detection (LOD) of approx. 4 nm.