Hierarchical Laser-Patterned Silver/Graphene Oxide\nHybrid SERS Sensor for Explosive Detection

Abstract

We demonstrate an ultrafast laser-ablated\nhierarchically patterned\nsilver nanoparticle/graphene oxide (AgNP/GO) hybrid surface-enhanced\nRaman scattering (SERS) substrate for highly sensitive and reproducible\ndetection of an explosive marker 2,4-dinitrotoluene (2,4-DNT). A hierarchical\nlaser-patterned silver sheet (Ag–S) is achieved by ultrafast\nlaser ablation in air with pulse energies of 25, 50, and 100 μJ.\nMultiple laser pulses at a wavelength of 800 nm and a pulse repetition\nrate of 50 fs at 1 kHz are directly focused on Ag–S to produce\nand deposit AgNPs onto Ag–S. The surface morphology of ablated\nAg–S was evaluated using atomic force microscopy, optical profilometry,\nand field emission scanning electron microscopy (FESEM). A rapid increase\nin the ablation rate with increasing laser energy was observed. Selected\narea Raman mapping is performed to understand the intensity and size\ndistribution of AgNPs on Ag–S. Further, GO was spin-coated\nonto the AgNPs produced by ultrafast ablation on Ag–S. The\nhierarchical laser-patterned AgNP/GO hybrid structure was characterized\nusing FESEM, high-resolution transmission electron microscopy, X-ray\ndiffraction, Fourier transform infrared spectroscopy, and Raman spectroscopy.\nFurther, hierarchical laser-patterned AgNP/GO hybrid structures have\nbeen utilized as SERS-active substrates for the selective detection\nof 2,4-DNT, an explosive marker. The developed SERS-active sensor\nshows good stability and high sensitivity up to picomolar (pM) concentration\nrange with a Raman intensity enhancement of ∼10¹⁰ for 2,4-DNT. The realized enhancement of SERS intensity is due to\nthe cumulative effect of GO coated on Ag–S as a proactive layer\nand AgNPs produced by ultrafast ablation.