We present a systematic study on
the fabrication, characterization
of versatile, and low-cost filter paper-based surface-enhanced Raman
spectroscopy (SERS) substrates loaded with salt-induced aggregated
Ag/Au nanoparticles (NPs). These were demonstrated as efficient SERS
substrates for the detection of multiple explosive molecules such
as picric acid (5 μM), 2,4-dinitrotoluene (1 μM), and
3-nitro-1,2,4-triazol-5-one (10 μM) along with a common dye
molecule (methylene blue, 5 nM). The concentrations of the dye and
explosive molecules in terms of mass represent 31.98 pg, 11.45 ng,
1.82 ng, and 13.06 ng, respectively. Silver (Ag) and gold (Au) colloidal
NPs were prepared by femtosecond laser (∼50 fs, 800 nm, 1 kHz)
ablation of Ag/Au-target immersed in distilled water. Subsequently,
the aggregated nanoparticles were achieved by mixing the pure Ag and
Au NPs with different concentrations of NaCl. These aggregated NPs
were characterized by UV–visible absorption and high-resolution
transmission electron microscopy techniques. The SERS substrates were
prepared by soaking the filter paper in aggregated NPs. The morphologies
of the paper substrates were investigated using field-emission scanning
electron microscopy technique. We have achieved superior enhancements
with high reproducibility and sensitivity for filter paper substrates
loaded with Ag/Au NPs mixed for an optimum concentration of 50 mM
NaCl.
Surface enhanced Raman spectroscopy (SERS) is a cutting edge analytical tool for trace analyte detection due to its highly sensitive, non-destructive and fingerprinting capability.
Herein we present results from our detailed studies on the fabrication of Ag@Au and Cu@Au alloy nanoparticles (NPs) using the femtosecond laser ablation in liquid technique. The NPs were obtained by ablating the pure Ag, Cu targets (bulk) in HAuCl 4 (5 mM) solution. The absorption properties of the obtained NPs colloids were characterized using UV-Visible absorption spectrometer and their size, shape, and crystallinity were investigated using the XRD, FESEM and TEM techniques. The fabricated NPs were utilized for sensing of explosive molecules such as 2,4,6-trinitrophenol (PA), 2,4-dinitrotoluene (DNT) and a common dye methylene blue (MB) using the surface enhanced Raman spectroscopy (SERS) technique. The detection limit in terms of weight was as low as few nano-grams in the case of nitroaromatic explosive compounds (PA, DNT) and few picograms in the case of a common dye molecule (MB). Typical enhancement factors achieved were estimated to be ∼10 4 , ∼10 5 , and ∼10 7 , respectively, for PA, DNT, and MB. The significance of the present work lies in exploring the performance of the prepared NPs being used as SERS substrates for explosives detection using a portable Raman instrument. Such capability enables one to carry the spectrometer to the point of interest in the field and evaluate any hazardous samples within a short period of time.
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