2,4-dinitrotoluene detected using portable Raman spectrometer and femtosecond laser fabricated Au–Ag nanoparticles and nanostructures

Abstract

We report results from our studies on the fabrication of bimetallic nanoparticles (NPs) and nanostructures (NSs) using femtosecond (∼50 fs) laser ablation technique. The NPs and NSs were achieved by immersing bulk targets with different Au–Ag compositions in acetone followed by ablation. We demonstrate their application towards detection of an explosive molecule of 2, 4-Dinitrotoluene, DNT (25 μM) using a portable Raman spectrometer (785 nm). A tuneable surface plasmon peak observed in the UV-Visible absorption spectra with varying Au proportions confirmed the formation of bimetallic NPs. The size, shape and crystallographic phases were investigated by transmission electron microscope (TEM) and selected area diffraction pattern (SAED). The surface morphology of fabricated NSs was characterized using field emission scanning electron microscope (FESEM). Both NPs and NSs were employed as Surface Enhanced Raman Scattering (SERS) substrates for sensing Methylene Blue (MB) and DNT. From the results obtained in this investigation we concluded that Au70Ag30 NPs/NSs exhibited superior SERS performance compared to pure Ag, Au and other compositions. A detection limit of ∼10−9 M for MB and ∼10−6 M for DNT was achieved with corresponding enhancement factors of ∼107 and ∼104. Furthermore, we have also observed a ‘factor of 3’ increase in the SERS intensity by simply drop casting Ag NPs on the gaps of Au70Ag30 NSs. This clearly demonstrates that individual NPs, NSs and NPs on NSs (hybrid SERS targets) can be achieved in a single experiment and in combination provide efficient means of detecting trace quantities of explosive molecules.