Laser ablation synthesis of bimetallic gold-palladium core@shell nanoparticles for trace detection of explosives

We report a facile synthesis strategy of bimetallic ultra-thin shell-wrapped gold-palladium (Au-Pd) core@shell nanoparticles (NPs) employing the liquid-assisted pulsed laser ablation (LA-PLA) technique. The bimetallic nanoparticles were prepared by double-step successive and single-step simultaneous laser ablation in the pres-ence of precursor solutions. The columbic attraction of the metal ions in the solution with the ablated metal nanoparticles ensures the uniform wrapping of ultra-thin shall layer through the electrostatic self-assembly. The (3-Aminopropyl)triethoxysilane (APTMS)-functionalized nanoparticles-based surface enhanced Raman scat-tering (SERS) substrates exhibit greatly amplified signals along with excellent signal reproducibility and repeatability with a relative standard deviation (RSD) value of less than 20 % for multiple substrates. The prepared core@shell NPs depict significantly improved SERS activity as compared to their corresponding monometallic samples for the methylene blue (MB) molecules down to the -1.38 x 10-12 M detectability. Owing to the ultra-thin Pd shell formation around the central Au core, the superior SERS activity was achieved with Au@Pd core@shell NPs through borrowing SERS activity for the trace-level detection of explosives ammonium nitrate (AN) and picric acid (PA) exhibiting detectability of -1.9 x 10-7 M and 3.49 x 10-8 M concentrations, respectively. To determine the influence of Au in the Pd@Au and Au@Pd core@shell NPs, nu-merical simulations were performed to explore the plasmonic response and electric-field distributions of bime-tallic NPs and compare them to monometallic PdNPs. Further, the Au@PdNPs-based substrates were utilized for the simultaneous identification of different concentrations of explosives from the fixed concentration of MB dye molecules with high specificity. The single-step laser ablation provides ultra-thin shell-coated Au@PdNPs with significantly improved and reproducible SERS activity compared to PdNPs.

Automated summary

We report a facile synthesis strategy of bimetallic ultra-thin shell-wrapped gold-palladium (Au-Pd) core@shell nanoparticles (NPs) employing the liquid-assisted pulsed laser ablation (LA-PLA) technique. The bimetallic nanoparticles were prepared by double-step successive and single-step simultaneous laser ablation in the presence of precursor solutions. The columbic attraction of the metal ions in the solution with the ablated metal nanoparticles ensures the uniform wrapping of ultra-thin shell layer through the electrostatic self-assembly.