The controlled pulsed laser deposition of Ag nanoparticle arrays for surface enhanced Raman scattering

Role of pH on Nanostructured SERS Active Substrates for Detection of Organic Dyes

Surface Enhanced Raman Spectroscopy is commonly used as analytical improvement to conventional Raman spectroscopy, able to respond to qualitative diagnostic enquiries, which involve low-concentrated molecular species in complex matrix. In this paper, we described fabrication, characterization and testing of a type of SERS-active substrates realized specifically to detect pigments in work of art. In particular, we detailed the SERS activity of nanostructured noble metal films deposited by pulsed laser ablation onto glass and polishing sheets substrates. The SERS response of the substrates was tested against the presence of some organic dyes in aqueous solutions. Measurements were performed at different pH values, in acidic or basic range, in order to investigate its role in the adsorption mechanism, thus fostering the SERS amplification. In addition, we checked the possible deterioration of the structural properties of the substrates that could occur in presence of alkaline or acidic environment. SERS activity of the substrates was tested against a commonly dye used as a SERS standard (Blue Methylene). Thereafter, substrates have been tested on two organic dyes (Alizarine red-S and Brazilwood), which had proven to be Raman active but present also either a weak Raman scattering cross section and/or a high fluorescence emission. The substrates have proven effective in amplifying Raman scattering of all dyes, quenching troubling fluorescence effects. Furthermore, they have proven to be stable in the pH range between 3 and 11. Furthermore, we carry out of vibrational DFT-calculation of dyes that provide a complete description of the observed SERS spectra.

An overview of surface-enhanced Raman scattering substrates by pulsed laser deposition technique: fundamentals and applications

Metallic nanoparticles (NPs), as an efficient substrate for surface-enhanced Raman scattering (SERS), attract much interests because of their various shapes and sizes. The appropriate size and morphology of metallic NPs are critical to serve as the substrate for achieving an efficient SERS. Pulsed laser deposition (PLD) is one of the feasible physical methods employed to synthesize metallic NPs with controllable sizes and surface characteristics. It has been recognized to be a successful tool for the deposition of SERS substrates due to its good controllability and high reproducibility in the manufacture of metallic NPs. This review provides an overview about the recent advances for the preparation of SERS substrates by PLD technique. The influences of parameters on the sizes and morphologies of metallic NPs during the deposition processes in PLD technique including laser output parameters, gas medium, liquid medium, substrate temperature, and properties of 3D substrate are presented. The applications of SERS substrates produced by PLD in the environmental monitoring and biomedical analysis are summarized. This knowledge could serve as a guideline for the researchers in exploring further applications of PLD technique in the production of SERS substrate.

Metal Nanoparticle Film Deposition by Femtosecond Laser Ablation at Atmospheric Pressure

Nanoparticle gold films were deposited using femtosecond laser ablation in argon at atmospheric pressure in an arrangement where a flat Au target was irradiated through a transparent substrate in close proximity. Spatially extended films were made by rastering the target and substrate assembly together in the laser beam. Fast imaging clearly showed pronounced narrowing of the ablation plume, which can be understood in terms of laser induced multiphoton ionisation and heating of the gas near the ablation site. Deposition was possible for target-substrate separation up to 2 mm. The equivalent thickness of the nanoparticle film was controlled in the range 0.4-28 nm by changing the target-substrate separation and the shot-to-shot spacing of ablation spot raster. The mean Feret diameter varied in the range 14-40 nm depending on the deposition conditions, and all the films showed a surface plasmon resonance at about 525 nm, which was nearly independent of the equivalent thickness. The technique can readily be applied to other materials for the fabrication of nanoparticulate films at atmospheric pressure.

Template growth of Au/Ag nanocomposites on phosphorene for sensitive SERS detection of pesticides

We report template growth and dense packing of noble metallic nanoparticles (NPs) on few-layer phosphorene for sensitive surface-enhanced Raman scattering (SERS) detection. Phosphorene obtained by electrochemical exfoliation serves as both the template and reductant in the fabrication of noble metallic NPs which are dispersed on phosphorene without aggregation or pile-up. The BP/Ag/Au and BP/Au/Ag nanocomposites with a nanogap structure exhibit excellent SERS sensitivity and reproducibility with respect to Rhodamine 6G. The BP/Au/Ag nanocomposite is further utilized as the SERS substrate for the detection of two fungicides, thiabendazole and thiram, and detection limits of 10^-7 and 10^-8 M are achieved. Template growth of Au/Ag nanocomposites is demonstrated to be a green strategy for the fabrication of SERS substrates and has large potential in applications such as pesticide detection.

SERS and DFT study of indigo adsorbed on silver nanostructured surface

Surface-enhanced Raman spectroscopy has emerged as a widely used tool in the identification of organic dyes in works of art. Indigo is among the most used organic pigment, its identification can therefore give important information about the provenience and the making of the investigated work of art. In this work, we combine Surface Enhanced Raman Spectroscopy (SERS) experiments with density functional theory (DFT) computations of the Raman frequencies of indigo and an indigo molecule adsorbed onto a silver surface made of 16 silver atoms. The SERS spectrum of a molecule adsorbed on a metallic surface, in fact, can differ from the corresponding Raman one. The knowledge and the comprehension of the SERS spectrum then are mandatory in dyes identification. Experimental SERS spectra were acquired using ad hoc SERS active substrates consisting of pulsed laser ablated silver nanoparticles deposited onto a polishing sheet. The polishing sheet surface roughness is able to remove some pigments grains from the surface of a work of art without damage. DFT calculations provide a good description of the observed SERS spectra, in particular, the indigo-Ag₁₆ structure gives a better description with respect to structures where only one or two silver atoms attached to the indigo molecule are considered.

Ultrafast laser printing of self-organized bimetallic nanotextures for multi-wavelength biosensing

Surface-enhanced spectroscopy (SES) techniques, including surface-enhanced photoluminescence (SEPL), Raman scattering (SERS) and infrared absorption (SEIRA), represent powerful biosensing modalities, allowing non-invasive label-free identification of various molecules and quantum emitters in the vicinity of nanotextured surfaces. Enhancement of multi-wavelength (vis-IR) excitation of analyte molecules of interest atop a single textured substrate could pave the way toward ultimate chemosensing performance and further widespread implementation of the SES-based approaches in various crucial areas, such as point-ofcare diagnostics. In this paper, an easy-to-implement ultrafast direct laser printing via partial spallation of thermally-thick silver films and subsequent large-scale magnetron deposition of nanometer-thick Au layers of variable thickness was implemented to produce bimetallic textured surfaces with the cascaded nanotopography. The produced bimetallic textures demonstrate the strong broadband plasmonic response over the entire visible spectral range. Such plasmonic performance was confirmed by convenient spectroscopy-free Red-Green-Blue (RGB) color analysis of the dark-field (DF) scattering images supported by numerical calculations of the electromagnetic (EM) “near-fields”, as well as comprehensive DF spectroscopic characterization. Bimetallic laser-printed nanotextures, which can be easily printed at ultrafast (square millimeters per second) rate, using galvanometric scanning, exhibited strong enhancement of the SEPL (up to 75-fold) and SERS (up to 10⁶ times) yields for the organic dye molecules excited at various wavelengths. Additionally, comprehensive optical and sensing characterization of the laser-printed bimetallic surface structures allows substantiating the convenient spectroscopy-free RGB color analysis as a valuable tool for predictive assessment of the plasmonic properties of the various irregularly and quasi-periodically nanotextured surfaces.

Catalytic Activity of Silicon Nanowires Decorated with Gold and Copper Nanoparticles Deposited by Pulsed Laser Ablation

Silicon nanowires (SiNWs) decorated by pulsed laser ablation with gold or copper nanoparticles (labeled as AuNPs@SiNWs and CuNPs@SiNWs) were investigated for their catalytic properties. Results demonstrated high catalytic performances in the C_aryl-N couplings and subsequent carbonylations for gold and copper catalysts, respectively, that have no precedents in the literature. The excellent activity, attested by the very high turn over number (TON) values, was due both to the uniform coverage along the NW length and to the absence of the chemical shell surrounding the metal nanoparticles (MeNPs). A high recyclability was also observed and can be ascribed to the strong covalent interaction at the Me-Si interface by virtue of metal "silicides" formation.

Decoration of silicon nanowires with silver nanoparticles for ultrasensitive surface enhanced Raman scattering

Silicon nanowires (Si NWs), produced by the chemical etching technique, were decorated with silver nanoparticles (NPs) produced at room temperature by the pulsed laser deposition (PLD) technique. Silver NPs were obtained by means of nanosecond pulsed laser ablation of a target in the presence of a controlled Ar atmosphere. Two different laser pulse numbers and Si NWs having different lengths were used to change the NP number density on the Si NW surface. The resulting Ag NP morphologies were studied by scanning electron microscopy imaging. The results show that this industrially compatible technological approach allows the coverage of the Si NW walls with Ag NPs with a strong control of the NP size distribution and spatial arrangement. The obtained Ag NP decorated Si NWs are free from chemicals contamination and there is no need of post deposition high temperature processes. The optical properties of Si NW arrays were investigated by reflectance spectroscopy that showed the presence of a plasmon related absorption peak, whose position and width is dependent on the Ag NP surface morphology. Coupling the huge surface-to-volume ratio of Si NW arrays with the plasmonic properties of silver nanoparticles resulted in a 3D structure suitable for very sensitive surface enhanced Raman scattering (SERS) applications, as demonstrated by the detection of Rhodamine 6G in aqueous solution at a concentration level of 10(-8) M.

Functionalization of silicon nanowire arrays by silver nanoparticles for the laser desorption ionization mass spectrometry analysis of vegetable oils

In this work, novel hybrid nanostructured surfaces, consisting of dense arrays of silicon nanowires (SiNWs) functionalized by Ag nanoparticles (AgNP/SiNWs), were used for the laser desorption/ionization time-of-flight mass spectrometry (LDI-TOF MS) analysis of some typical unsaturated food components (e.g. squalene, oleic acid) to assess their MS performance. The synthesis of the novel platforms is an easy, cost-effective process based on the maskless wet-etching preparation at room temperature of SiNWs followed by their decoration with AgNPs, produced by pulsed laser deposition. No particular surface pretreatment or addition of organic matrixes/ionizers was necessary. Moreover, oil extracts (e.g. extra virgin olive oil, peanut oil) could be investigated on AgNP/SiNWs surfaces, revealing their different MS profiles. It was shown that such substrates operate at reduced laser energy, typically generating intense silver cluster ions and analyte adducts. A comparison with bare SiNWs was also performed, indicating the importance of AgNP density on NW surface. In this case, desorption/ionization on silicon was invoked as probable LDI mechanism. Finally, the influence of SiNW length and surface composition on MS results was assessed. The combination of typical properties of SiNWs (hydrophobicity, antireflectivity) with ionization ability of metal NPs can be a valid methodology for the further development of nanostructured surfaces in LDI-TOF MS applications. Copyright © 2016 John Wiley & Sons, Ltd.

Self-assembled plasmonic templates produced by microwave annealing: applications to surface-enhanced Raman scattering

Perhaps the simplest method for creating metal nanoparticles on a substrate is by driving their self-assembly with the thermal annealing of a thin metal film. By properly tuning the annealing parameters one hopes to discover a recipe that allows the pre-determined design of the NP arrangement. However, thermal treatment is known for detrimental effects and is not really the manufacturer's route of choice when it comes to large-scale applications. An alternative method is the use of microwave annealing, a method that has never been applied for metal processing, due to the high reflectance of microwave radiation at the surface of a metal. However, in this work we challenge the widely used nanostructuring methods by proving the microwave's annealing ability to produce plasmonic templates, out of extremely thin metal films, by simply using a domestic microwave oven apparatus. We show that this process is generic and independent of the deposition method used for the metal and we further quantify the suitability of these plasmonic templates for use in surface-enhanced Raman scattering applications.

Methods and strategies for the synthesis of diverse nanoparticles and their applications: a comprehensive overview

Various methods to synthesize diverse nanoparticles with their different applications.

Comparison of nanosecond and femtosecond pulsed laser deposition of silver nanoparticle films

Nanoparticle (NP) films of silver were prepared using nanosecond (ns) and femtosecond (fs) pulsed laser deposition (PLD) in vacuum. The flux and energy distribution of the ions in the plasma part of the ablation plume were measured using a Langmuir ion probe. The deposition energy efficiencies of ns and fs silver PLD were also compared. For equivalent thickness up to ∼3 nm the NPs made by ns-PLD are well separated and roughly circular, but for higher thicknesses the NPs begin to coalesce. For equivalent thickness up to 7 nm the fs films are comprised of well separated NPs, though the mean NP size and the surface coverage increase with equivalent thickness. The mean Feret diameter for both ns- and fs-PLD films increases with increasing equivalent solid-density thickness. The surface plasmon resonance peak was observed to red shift for both ns- and fs-PLD films as the equivalent solid-density thickness was increased from 1 nm to 7 nm.

Nanolayer biofilm coated on magnetic nanoparticles by using a dielectric barrier discharge glow plasma fluidized bed for immobilizing an antimicrobial peptide

Using the monomer of acrylic acid and the novel technique of using a dielectric barrier discharge glow plasma fluidized bed (GPFB), a nanolayer biofilm of polyacrylic acid (PAA) was uniformly coated on the surface of magnetic nickel nanoparticles (NPs). Transmission electron microscopy, Fourier transform infrared spectroscopy, and x-ray photoelectron spectroscopy, etc, were used to characterize the modified NPs. The thickness of the biofilm was about 2 nm when the NPs were treated using the GPFB once, and the discharging conditions affected the density of the carboxyl group obviously. The PAA acting as an adhesion layer was used to immobilize the antimicrobial peptide LL-37, to kill the bacteria of Escherichia coli (E. coli), and the results indicated that the modified nickel NPs immobilizing a certain concentration of LL-37 could kill the bacteria effectively.