Trace-Level Detection of Secondary Explosives Using Hybrid Silver-Gold Nanoparticles and Nanostructures Achieved with Femtosecond Laser Ablation

Hybrid silver-gold targets were achieved by effortless mixing of pure silver (Ag) and gold (Au) metals at different ratios (Ag0.65Au0.35, Ag0.5Au0.5, and Ag0.35Au0.65) and embracing a manual melting process. The obtained targets were ablated by ultrafast (similar to 40 fs) laser pulses in acetone ensuing the fabrication of Ag-Au bimetallic nanoparticles (NPs) and nanostructures (NSs) in a single experiment. UV-visible extinction spectra of Ag-Au colloids demonstrated the tuning of localized surface plasmon resonance (LSPR) in the spectral range of 406-524 nm. The morphologies of NSs were investigated by the field emission scanning electron microscopy (FESEM) technique. Ag-Au NPs and NSs were utilized as surface enhanced Raman scattering (SERS) platforms to detect secondary explosive molecules such as 1,1-diamino-2,2-dinitroethene (FOX-7, 5 mu M concentration) and 1-nitro pyrazole (1NPZ, 20 nM concentration). Our experimental observations clearly demonstrated that the increment in gold percentage reduced the surface activity of Ag-Au NPs/NSs. The estimated enhancement factors (EFs) from the SERS data were typically >10(8). Our detailed investigations revealed that the NPs and NSs of Ag0.65Au0.35 exhibited significant EFs compared to other ratios and pure metals of Ag and Au.