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Detection of Trace-Level Nitroaromatic Explosives by 1-Pyreneiodide-Ligated Luminescent Gold Nanostructures and Their Forensic Applications.

By attaching the1-pyreneiodide ancillary ligand to the surface of polyvinylpyrrolidone-stabilized gold (Au:PVP) cluster or the cetyltrimethyl ammonium bromide-stabilized gold (Au:CTAB) nanorod, a new class of luminescent mixed ligand-stabilized gold nanostructures is synthesized. This postsynthetic surface modification method followed by us is a comparatively easier and hassle-free technique to acquire surface-active luminescent "functional nanomaterials". Careful analyses of transmission electron microscopy images revealed that the sizes of these Au-clusters or Au-nanorods remain unchanged without any noticeable aggregation in the medium. Owing to the formation of an excimer within the neighboring pyrenes mounted on the surface of core nanostructures (i.e., Au:PVP nanocluster and Au:CTAB nanorod), the resulting pyrene-grafted nanocomposites exhibit strong emission characteristics. The strong excimer emission is significantly quenched in the presence of electron-deficient chemical inputs, and this phenomenon can be used for analytical purposes. Using these luminescent Au-nanomaterials, we demonstrate a selective detection and sensing of trace-level nitroaromatic explosives (e.g., trinitrotoluene, trinitrophenol (TNP), dinitrotoluene, 4-nitrotoluene, etc.). It was observed that the Py-Au:PVP nanocluster is equally effective for explosive detection in both solution and solid phases with the limit of detection up to 10 nanomolar. A high Stern-Volmer constant of up to 3.88 × 106 M-1 was seen in the case of TNP in anhydrous methanol at 298 K. The deactivation pathway operating within the Py-Au:PVP nanocluster and the analytes is thought to be a result of a predominating static quenching process, where a nonfluorescent D-A supramolecular adduct is formed in the medium. Py-Au:PVP has also been successfully used to develop latent fingerprints from nonporous surfaces under an exposure of 365 nm UV light. The results suggest that these new composite materials could behave as potential "functional nanomaterials", which might be a promising alternative for on-the-spot detection of explosive traces as well as for easy visualization of latent fingerprints.