Determining the laser-induced release probability of a nanoparticle from a soft substrate.

This Letter presents a study of laser-induced nanoparticle release from a soft substrate in air under different conditions. A continuous wave (CW) laser heats a nanoparticle and causes a rapid thermal expansion of the substrate, which gives an upward momentum that releases the nanoparticle from the substrate. The release probability of different nanoparticles from different substrates under different laser intensities is studied. The effects of surface properties of substrates and surface charges of the nanoparticles on the release are also investigated. The mechanism of nanoparticle release demonstrated in this work is different from that of laser-induced forward transfer (LIFT). Owing to the simplicity of this technology and the wide availability of commercial nanoparticles, this nanoparticle release technology may find applications in nanoparticle characterization and nanomanufacturing.

Laser beam steering automation with an Arduino-based CNC shield for standoff femtosecond filament-induced breakdown spectroscopic studies.

In this study, we report a novel, to the best of our knowledge, instrumentation procedure in the automation of laser beam steering for raster/spiral scanning of the samples used in standoff femtosecond laser-induced breakdown spectroscopy (LIBS) experiments. We have used a readily available and easy-to-handle Arduino-based computerized numerical control (CNC) shield along with the free software, universal G-code sender, for the automation. Standoff femtosecond filamentation-induced breakdown spectra (St-Fs-FIBS) of metals, three compositions of Ag-Au alloy, and polyvinyl chloride, unplasticized polyvinyl chloride, and chlorinated polyvinyl chloride plastic samples were recorded using the developed automated experimental setup. The St-Fs-FIBS spectra were recorded at a standoff distance of ∼5m utilizing a simple hand-held spectrometer. Furthermore, principal component analysis technique was utilized for the successful classification of three compositions of Au-Ag alloy spectra using their St-Fs-FIBS spectral data.

SERS based detection of multiple analytes from dye/explosive mixtures using picosecond laser fabricated gold nanoparticles and nanostructures.

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 report the detection of multiple analytes from various mixtures using gold nanoparticles (NPs) and nanostructures (NSs) as SERS platforms. NPs and NSs were achieved through the simple approach of laser ablation in liquids (LAL) and their morphological studies were conducted with a UV-Visible absorption spectrometer, a high resolution transmission electron microscope (HRTEM) and a field emission scanning electron microscope (FESEM). The fabricated NPs/NSs allowed the sensitive and selective detection of different mixed compounds containing (i) rhodamine 6G (Rh6G) and methylene blue (MB), (ii) crystal violet (CV) and malachite green (MG), (iii) picric acid (explosive) and MB (dye), (iv) picric acid and 3-nitro-1,2,4- triazol-5-one (explosive, NTO) and (v) picric acid and 2,4-dinitrotoluene (explosive, DNT) using a portable Raman spectrometer. Thus, the obtained results demonstrate the capability of fabricated SERS substrates in identifying explosives and dyes from various mixtures. This could pave a new way for simultaneous detection of multiple analytes in real field applications.

Femtosecond laser induced breakdown spectroscopy based standoff detection of explosives and discrimination using principal component analysis.

We report the standoff (up to ~2 m) and remote (~8.5 m) detection of novel high energy materials/explosive molecules (Nitroimidazoles and Nitropyrazoles) using the technique of femtosecond laser induced breakdown spectroscopy (LIBS). We utilized two different collection systems (a) ME-OCT-0007 (commercially available) and (b) Schmidt-Cassegrain telescope for these experiments. In conjunction with LIBS data, principal component analysis was employed to discriminate/classify the explosives and the obtained results in both configurations are compared. Different aspects influencing the LIBS signal strength at far distances such as fluence at target, efficiency of collection system etc. are discussed.

Effect of wavelength and liquid on formation of Ag, Au, Ag/Au nanoparticles via picosecond laser ablation and SERS-based detection of DMMP.

The present study investigates the effects of input wavelength (1064, 532, and 355 nm) and surrounding liquid environment (distilled water and aqueous NaCl solution) on the picosecond laser ablation on silver (Ag), gold (Au), and Ag/Au alloy targets. The efficacy of the laser ablation technique was meticulously evaluated by analyzing the ablation rates, surface plasmon resonance peak positions, and particle size distributions of the obtained colloids. The nanoparticles (NPs) were characterized using the techniques of UV-visible absorption, transmission electron microscopy, and energy-dispersive X-ray spectroscopy. Furthermore, NPs of various sizes ranging from 6 to 35 nm were loaded onto a filter paper by a simple and effective drop-casting approach to achieve flexible surface-enhanced Raman spectroscopy (SERS) substrates/sensors. These substrates were tested using a simple, portable Raman device to identify various hazardous chemicals (malachite green, methyl salicylate, and thiram). The stability of the substrates was also systematically investigated by determining the decay percentages in the SERS signals over 60 days. The optimized SERS substrate was subsequently employed to detect chemical warfare agent (CWA) simulants such as methyl salicylate (a CWA simulant for sulfur mustard) and dimethyl methyl phosphonate (has some structural similarities to the G-series nerve agents) at different laser excitations (325, 532, and 633 nm). A notably higher SERS efficiency for CWA simulants was observed at a 325 nm Raman excitation. Our findings reveal that a higher ablation yield was observed at IR irradiation than those obtained at the other wavelengths. A size decrease of the NPs was noticed by changing the liquid environment to an electrolyte. These findings have significant implications for developing more efficient and stable SERS substrates for chemical detection applications.

Femtosecond laser patterned silicon embedded with gold nanostars as a hybrid SERS substrate for pesticide detection.

We have developed simple and cost-effective surface-enhanced Raman scattering (SERS) substrates for the trace detection of pesticide (thiram and thiabendazole) and dye (methylene blue and Nile blue) molecules. Surface patterns (micro/nanostructures) on silicon (Si) substrates were fabricated using the technique of femtosecond (fs) laser ablation in ambient air. Different surface patterns were achieved by tuning the number of laser pulses per unit area (4200, 8400, 42 000, and 84 000 pulses per mm2) on Si. Subsequently, chemically synthesized gold (Au) nanostars were embedded in these laser-patterned areas of Si to achieve a plasmonic active hybrid SERS substrate. Further, the SERS performance of the as-prepared Au nanostar embedded Si substrates were tested with different probe molecules. The as-prepared substrates allowed us to detect a minimum concentration of 0.1 ppm in the case of thiram, 1 ppm in the case of thiabendazole (TBZ), 1.6 ppb in the case of methylene blue (MB), and 1.8 ppb in case of Nile blue (NB). All these were achieved using a simple, field-deployable, portable Raman spectrometer. Additionally, the optimized SERS substrate demonstrated ∼21 times higher SERS enhancement than the Au nanostar embedded plain Si substrate. Furthermore, the optimized SERS platform was utilized to detect a mixture of dyes (MB + NB) and pesticides (thiram + TBZ). The possible reasons for the observed additional enhancement are elucidated.

Picosecond Laser-Ablated Nanoparticles Loaded Filter Paper for SERS-Based Trace Detection of Thiram, 1,3,5-Trinitroperhydro-1,3,5-triazine (RDX), and Nile Blue.

Recently, filter paper (FP)-based surface-enhanced Raman scattering (SERS) substrates have stimulated significant attention owing to their promising advantages such as being low-cost, easy to handle, and practically suitable for real-field applications in comparison to the solid-based substrates. Herein, a simple and versatile approach of laser-ablation in liquid for the fabrication of silver (Ag)-gold (Au) alloy nanoparticles (NPs). Next, the optimization of flexible base substrate (sandpaper, printing paper, and FP) and the FP the soaking time (5−60 min) was studied. Further, the optimized FP with 30 min-soaked SERS sensors were exploited to detect minuscule concentrations of pesticide (thiram-50 nM), dye (Nile blue-5 nM), and an explosive (RDX-1,3,5-Trinitroperhydro-1,3,5-triazine-100 nM) molecule. Interestingly, a prominent SERS effect was observed from the Au NPs exhibiting satisfactory reproducibility in the SERS signals over ~1 cm2 area for all of the molecules inspected with enhancement factors of ~105 and relative standard deviation values of <15%. Furthermore, traces of pesticide residues on the surface of a banana and RDX on the glass slide were swabbed with the optimized FP substrate and successfully recorded the SERS spectra using a portable Raman spectrometer. This signifies the great potential application of such low-cost, flexible substrates in the future real-life fields.

Hybrid Surface-Enhanced Raman Scattering Substrates for the Trace Detection of Ammonium Nitrate, Thiram, and Nile Blue.

We report the fabrication and performance evaluation of hybrid surface-enhanced Raman scattering (SERS) substrates involving laser ablation and chemical routes for the trace-level detection of various analyte molecules. Initially, picosecond laser ablation experiments under ambient conditions were performed on pure silver (Ag) and gold (Au) substrates to achieve distinct nanosized features on the surface. The properties of the generated surface features on laser-processed portions of Ag/Au targets were systematically analyzed using UV-visible reflection and field emission scanning electron microscopy studies. Later, hybrid-SERS substrates were achieved by grafting the chemically synthesized Au nanostars on the plain and laser-processed plasmonic targets. Subsequently, we employed these as SERS platforms for the detection of a pesticide (thiram), a molecule used in explosive compositions [ammonium nitrate (AN)], and a dye molecule [Nile blue (NB)]. A comparative SERS study between the Au nanostar-decorated bare glass, silicon, Ag, Au, and laser-processed Ag and Au targets has been established. Our studies and the obtained data have unambiguously determined that laser-processed Ag structures have demonstrated reasonably good enhancements in the Raman signal intensities for distinct analytes among other substrates. Importantly, the fabricated hybrid SERS substrate of "Au nanostar-decorated laser-processed Ag" exhibited up to eight times enhancement in the SERS intensity compared to laser-processed Ag (without nanostars), as well as up to three times enhancement than the Au nanostar-loaded plain Ag substrates. Additionally, the achieved detection limits from the Au nanostar-decorated laser-processed Ag SERS substrate were ∼50 pM, ∼5 nM, and ∼5 µM for NB, thiram, and AN, respectively. The estimated enhancement factors accomplished from the Au nanostar-decorated laser-processed Ag substrate were ∼106, ∼106, and ∼104 for NB, thiram, and AN, respectively.

Instantaneous trace detection of nitro-explosives and mixtures with nanotextured silicon decorated with Ag-Au alloy nanoparticles using the SERS technique.

The development of recyclable surface enhanced Raman scattering (SERS) based sensors has been in huge demand for trace level explosives detection. A simple, hybrid Silicon (Si) nanotextured target-based SERS platform is fabricated through patterning micro square arrays (MSA) on Si using femtosecond (fs) laser ablation technique at different fluences. Using the hybrid target Si MSA substrate loaded/decorated with Ag-Au alloy NPs (obtained using femtosecond ablation in liquids) we demonstrate the trace level detection of organic nitro-explosives [picric acid (PA), 2,4-dinitrotoluene (DNT), and 1, 3, 5-trinitroperhydro-1, 3, 5-triazine (RDX)] and their mixtures. The microstructures/nanostructures of MSA fabricated at an input fluence of 9.55 J/cm2, and decorated with Ag-Au alloy NPs, exhibited exceptional SERS enhancement factors (EFs) up to ∼1010 for MB, ∼106 for PA, and ∼104 for RDX with the detection limits obtained being âˆ¼5 pM, ∼36 nM, and ∼400 nM for MB, PA and RDX respectively. Furthermore, we demonstrate these SERS substrates possess good reproducibility (RSD values < 15%) and a superior performance compared to a commercial Ag substrate (SERSitive, Poland). Three binary mixtures, i.e. MB-PA, MB-DNT, PA-DNT at different concentrations, were also investigated using the same SERS substrate to test the efficacy. Further, the SERS spectra of dyes, explosives, and complex mixtures were utilized for discrimination/classification using principal component analysis.

Ag/Au Nanoparticle-Loaded Paper-Based Versatile Surface-Enhanced Raman Spectroscopy Substrates for Multiple Explosives Detection.

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.