Performance enhancement of paper-based SERS chips by shell-isolated nanoparticle-enhanced Raman spectroscopy

Paper-based flexible surface-enhanced Raman scattering (SERS) chips have been demonstrated to have great potential for future practical applications in point-of-care testing (POCT) due to the potentials of massive fabrication, low cost, efficient sample collection and short signal acquisition time. In this work, common filter paper and Ag@SiO₂core-shell nanoparticles (NP) have been utilized to fabricate SERS chips based on shell‐isolated nanoparticle‐enhanced Raman spectroscopy (SHINERS). The SERS performance of the chips for POCT applications was systematically investigated. We used crystal violet as the model molecule to study the influence of the size of the Ag core and the thickness of the SiO₂coating layer on the SERS activity and then the morphology optimized Ag@SiO₂core-shell NPs was employed to detect thiram. By utilizing the smartphone as a miniaturized Raman spectral analyzer, high SERS sensitivity of thiram with a detection limit of 10⁻⁹M was obtained. The study on the stability of the SERS chips shows that a SiO₂shell of 3 nm can effectively protect the as-prepared SERS chips against oxidation in ambient atmosphere without seriously weakening the SERS sensitivity. Our results indicated that the SERS chips by SHINERS had great potential of practical application, such as pesticide residues detection in POCT.     

Silver nanoparticles deposited on anodic aluminum oxide template using magnetron sputtering for surface-enhanced Raman scattering substrate

Low-cost and highly sensitive surface-enhanced Raman scattering (SERS) substrates have been fabricated by a simple anodizing process and a magnetron sputtering deposition. The substrates, which consist of silver nanoparticles embedded on anodic aluminum oxide (AAO) templates, are investigated by a scanning electron microscope and a confocal Raman spectroscopy. The SERS activities are demonstrated by Raman scattering from adsorbed solutions of methylene blue and pyridine on the SERS substrate surface. The most optimized SERS substrate contains the silver nanoparticles, with a size distribution of 10-30 nm, deposited on the AAO template. From a calculation, the SERS enhancement factor is as high as 8.5 × 10⁷, which suggests strong potentials for direct applications in the chemical detection and analyses.     

Ag nanoclusters synthesized by successive ionic layer deposition method and their characterization

The possibilities of successive ionic layer deposition technology for synthesizing the Ag nanoclusters and nanolayers were analyzed in present article. It was shown that this technology, based on successive treatments of appropriate substrates in solution of cations and anions, is acceptable for the controllable forming of the Ag nanoparticles at the surface of different substrates. Results related to characterization of the Ag nanoclusters synthesized using Ag(NH₃)₂NO₃ or AgNO₃ precursors were discussed. It was found that the concentration and the size of the Ag nanoparticles deposited on a surface of fused quartz, silica gel, and monocrystalline silicon can be controlled by varying composition and pH of the reagent solutions as well as the number of the deposition cycles. It was established that the size of Ag nanoclusters depending on a synthesis conditions may vary from 1–5 nm to 500 nm. Model explained the growth of Ag clusters during successive ionic layer deposition was discussed as well.     

Surface-enhanced Raman scattering substrate of silver nanoparticles depositing on AAO template fabricated by magnetron sputtering

In this report, we describe a fabrication process of low-cost and highly sensitive SERS substrates by using a simple anodizing setup and a low-energy magnetron sputtering method. The structure of the SERS substrates consists of silver nanoparticles deposited on a layer of anodic aluminum oxide (AAO) template. The fabricated SERS substrates are investigated by a scanning electron microscope (SEM), a transmission electron microscope (TEM), and a confocal Raman spectroscope. We have verified from the surface morphology that the fabricated SERS substrates consist of high-density round-shape silver nanoparticles where their size distribution ranges from 10 to 30 nm on the top and the bottom of nanopores. The surface-enhanced Raman scattering activities of these nanostructures are demonstrated using methylene blue (MB) as probing molecules. The detection limit of 10⁻⁸ M can be achieved from this SERS substrate.     

Surface-enhanced Raman scattering substrate of silver nanoparticles depositing on AAO template fabricated by magnetron sputtering

In this report, we describe a fabrication process of low-cost and highly sensitive SERS substrates by using a simple anodizing setup and a low-energy magnetron sputtering method. The structure of the SERS substrates consists of silver nanoparticles deposited on a layer of anodic aluminum oxide (AAO) template. The fabricated SERS substrates are investigated by a scanning electron microscope (SEM), a transmission electron microscope (TEM), and a confocal Raman spectroscope. We have verified from the surface morphology that the fabricated SERS substrates consist of high-density round-shape silver nanoparticles where their size distribution ranges from 10 to 30 nm on the top and the bottom of nanopores. The surface-enhanced Raman scattering activities of these nanostructures are demonstrated using methylene blue (MB) as probing molecules. The detection limit of 10⁻⁸ M can be achieved from this SERS substrate.     

Fabrication and characterization of Ag-SiO2 composite hollow nanospheres

Ag-SiO₂ composite hollow nanospheres were synthesized by impregnation of hollow silica nanospheres (HSNSs), which were prepared by templating CaCO₃ nanoparticles, in [Ag(NH₃)₂]NO₃ aqueous solution followed by heat treatment. The straightforward process generates composite materials containing Ag nanoparticles, with the average size of 6–10 nm in diameter, uniformly dispersed and mainly distributed on the shells or between the spaces of the HSNSs. The Ag-supported HSNSs were characterized through TEM, EDS, and XPS. Furthermore, ASS, XRD and UV-Vis analyses demonstrated that higher loading efficiency could be achieved under the optimum loading conditions of a silver precursor solution of 0.08 M, pH = 9.0 and HSNSs with a BET surface area of 830.4 m²/g.     

Magnetron Sputtering Deposition of Ag/TiO2 Nanocomposite Thin Films for Repeatable and Multicolor Photochromic Applications on Flexible Substrates

It is reported on a reactive magnetron sputtering‐based deposition method to synthesize, at room temperature, photochromic nanocomposite thin films consisting of Ag nanoparticles sandwiched between nanoporous TiO₂ layers. The fabrication process is compatible with large‐scale production and functional flexible substrates. It is shown that when TiO₂ is deposited in the metallic mode, the formation of Ag metal nanoparticles induces localized surface plasmon resonances in the visible range and therefore the as‐deposited samples are colored. In contrast, when TiO₂ is deposited in the compound mode, the trilayer samples are colorless because silver oxidizes during TiO₂ deposition. It is demonstrated that the colorless samples can be colored under ultraviolet (UV) laser exposure at 244 nm due to the reduction of oxidized silver and the formation of metallic Ag nanoparticles. Moreover, irradiation at 647 nm wavelength of colored samples (as‐prepared or after UV exposure) gives rise to changes in the particle morphology that strongly modifies the film absorbance and results in a color transition from blue to orange. The choice of the irradiation wavelength allows controlling the color saturation of the sample up to the complete discoloration by using a visible laser at 488 nm. All these photochromic mechanisms are repeatable during cyclic processes.     

Directly ultraviolet photochemical deposition of silver nanoparticles on silica spheres: Preparation and characterization

A simple method was developed to directly deposit silver nanoparticles on the surface of silica spheres. The photochemical reduction was carried out by ultraviolet irradiation in air atmosphere at room temperature. The [Ag(NH₃)₂]⁺was reduced to silver atoms upon ultraviolet irradiation. Silver atoms subsequently deposited on the surface of silica spheres and agglomerated into silver nanoparticles. Silica spheres with silver nanoparticles of different size and density can be simply controlled by adjusting the UV-light irradiation time. The silver nanoparticles deposited on silica spheres were characterized by X-ray photoelectron spectroscopy, X-ray diffraction, transmission electron microscopy, and field emission scanning electron microscopy.     

Dependence of surface-enhanced infrared absorption (SEIRA) enhancement and spectral quality on the choice of underlying substrate: a closer look at silver (Ag) films prepared by physical vapor deposition (PVD)

Silver (Ag) films of varying thickness were simultaneously deposited using physical vapor deposition (PVD) onto six infrared (IR) substrates (BaF(2), CaF(2), Ge, AMTIR, KRS-5, and ZnSe) in order to correlate the morphology of the deposited film with optimal SEIRA response and spectral band symmetry and quality. Significant differences were observed in the surface morphology of the deposited silver films, the degree of enhancement provided, and the spectral appearance of para-nitrobenzoic acid (PNBA) cast films for each silver-coated substrate. These differences were attributed to each substrate's chemical properties, which dictate the morphology of the Ag film and ultimately determine the spectral appearance of the adsorbed analyte and the magnitude of SEIRA enhancement. Routine SEIRA enhancement factors (EFs) for all substrates were between 5 and 150. For single-step Ag depositions, the following ranking identifies the greatest SEIRA enhancement factor and the maximum absorption of the 1345 cm(-1) spectral marker of PNBA at the optimal silver thickness for each substrate: BaF(2) (EF = 85 ± 19, 0.059 A, 10 nm Ag) > CaF(2) (EF = 75 ± 30, 0.052 A, 10 nm Ag) > Ge (EF = 45 ± 8, 0.019 A, 5 nm Ag) > AMTIR (EF = 38 ± 8, 0.024 A, 15 nm Ag) > KRS-5 (EF = 24 ± 1, 0.015 A, 12 nm Ag) > ZnSe (EF = 9 ± 5, 0.008 A, 8 nm Ag). A two-step deposition provides 59% larger EFs than single-step depositions of Ag on CaF(2). A maximum EF of 147 was calculated for a cast film of PNBA (surface coverage = 341 ng/cm(2)) on a 10 nm two-step Ag film on CaF(2) (0.102 A, 1345 cm(-1) symmetric NO(2) stretching band). The morphology of the two-step Ag film has smaller particles and greater particle density than the single-step Ag film.     

Fabrication and characterization of silver/polystyrene nanospheres with more complete coverage of silver nano-shell

In the present work, the silver/polystyrene nanospheres with more uniform particle size and more complete coverage of silver nano-shell have been prepared. The formation of the silver/polystyrene nanospheres was realized by adopting a “one-pot” route. The styrene monomer was at first emulsified by OP-10 to form micelle. The mercaptoethanol played an important role in the process of forming silver/polystyrene shell-core structure. Polymerization of styrene was initiated by the redox system composed of AgNO₃/NaBH₄. When Ag⁺ ion was reduced to Ag, it deposited on the surface of the polystyrene nanoparticle to form uniform metallic nanoshell. The morphology of the silver/polystyrene nanospheres have been characterized by Fourier transform infrared spectrometry, X-ray diffraction, transmission electron microscopy, atomic force microscopy, dynamic light scattering and UV-visible absorption measurements.     

The effects of nanoparticle shape on electrical conductivity of Ag nanomaterials

Silver nanomaterials have a wide application in printed electronics due to their excellent electrical conductivity. However, less studies were done to investigate the effects of nanoparticle shape on conductance. In this work, silver nanocubes with edge length of 45 nm and silver nanospheres with the same diameter of 45 nm were successfully prepared via polyol synthesis, and then characterized by scan electron microscopy, transmission electron microscopy, ultraviolet–visible spectrophotometry and dynamic light scattering. Subsequently, the electric conductivities of pastes filled with Ag nanocubes and Ag nanospheres were measured using four point probe resistance measurement by coating on glasses, the result of which showed that, the conductance of Ag nanospheres paste was much superior to that of Ag nanocubes paste with the same silver content and with or without the same mass ratio of m_(Ag)/m_(PVP). The possible underlying mechanism was further deeply analyzed.     

Investigation of low resistance transparent MoO3/Ag/MoO3 multilayer and application as anode in organic solar cells

Depending on the resistivity and transmittance, transparent conductive oxides (TCO) are widely used in thin film optoelectronic devices. Thus doped In₂O₃ (ITO), ZnO, SnO₂ are commercially developed. However, the deposition process of these films need sputtering and/or heating cycle, which has negative effect on the performances of the organic devices due to the sputtering and heat damages. Therefore a thermally evaporable, low resistance, transparent electrode, deposited onto substrates room temperature, has to be developed to overcome these difficulties. For these reasons combination of dielectric materials and metal multilayer has been proposed to achieve high transparent conductive oxides. In this work the different structures probed were: MoO₃ (45 nm)/Ag (x nm)/MoO₃ (37.5 nm), with x = 5-15 nm. The measure of the electrical conductivity of the structures shows that there is a threshold value of the silver thickness: below 10 nm the films are semiconductor, from 10 nm and above the films are conductor. However, the transmittance of the structures decreases with the silver thickness, therefore the optimum Ag thickness is 10 nm. A structure MoO₃ (45 nm)/Ag (10 nm)/MoO₃ (37.5 nm) resulted with a resistivity of 8 × 10^− 5 Ω cm and a transmittance, at around 600 nm, of 80%. Such multilayer structure can be used as anode in organic solar cells according to the device anode/CuPc/C₆₀/Alq₃/Al. We have already shown that when the anode of the cells is an ITO film the introduction of a thin (3 nm) MoO₃ layer at the interface anode (ITO)/organic electron donor (CuPc) allows reducing the energy barrier due to the difference between the work function of ITO and the highest occupied molecular orbital of CuPc [1]. This property has been used in the present work to achieve a high hole transfer efficiency between the CuPc and the anode. For comparison MoO₃/Ag/MoO₃/CuPc/C₆₀/Alq₃/Al and ITO/MoO₃/CuPc/C₆₀/Alq3/Al solar cells have been deposited in the same run. These devices exhibit efficiency of the same order of magnitude.     

Nanoparticle‐Enhanced Silver‐Nanowire Plasmonic Electrodes for High‐Performance Organic Optoelectronic Devices

Improved performance in plasmonic organic solar cells (OSCs) and organic light‐emitting diodes (OLEDs) via strong plasmon‐coupling effects generated by aligned silver nanowire (AgNW) transparent electrodes decorated with core–shell silver–silica nanoparticles (Ag@SiO₂NPs) is demonstrated. NP‐enhanced plasmonic AgNW (Ag@SiO₂NP–AgNW) electrodes enable substantially enhanced radiative emission and light absorption efficiency due to strong hybridized plasmon coupling between localized surface plasmons (LSPs) and propagating surface plasmon polaritons (SPPs) modes, which leads to improved device performance in organic optoelectronic devices (OODs). The discrete dipole approximation (DDA) calculation of the electric field verifies a strongly enhanced plasmon‐coupling effect caused by decorating core–shell Ag@SiO₂NPs onto the AgNWs. Notably, an electroluminescence efficiency of 25.33 cd A^?1 (at 3.2 V) and a power efficiency of 25.14 lm W^?1 (3.0 V) in OLEDs, as well as a power conversion efficiency (PCE) value of 9.19% in OSCs are achieved using hybrid Ag@SiO₂NP–AgNW films. These are the highest values reported to date for optoelectronic devices based on AgNW electrodes. This work provides a new design platform to fabricate high‐performance OODs, which can be further explored in various plasmonic and optoelectronic devices.     

Tunable and highly reproducible surface-enhanced Raman scattering substrates made from large-scale nanoparticle arrays based on periodically poled LiNbO3 templates

Abstract

This work describes novel surface-enhanced Raman scattering (SERS) substrates based on ferroelectric periodically poled LiNbO₃ templates. The templates comprise silver nanoparticles (AgNPs), the size and position of which are tailored by ferroelectric lithography. The substrate has uniform and large sampling areas that show SERS effective with excellent signal reproducibility, for which the fabrication protocol is advantageous in its simplicity. We demonstrate ferroelectric-based SERS substrates with particle sizes ranging from 30 to 70 nm and present tunable SERS effect from Raman active 4-mercaptopyridine molecules attached to AgNPs when excited by a laser source at 514 nm.     

Preparation of silver nanoparticles dispersed in polyacrylonitrile nanofiber film spun by electrospinning

Ag nanoparticles dispersed in polyacrylonitrile (PAN) nanofiber film spun by electrospinning were in situ prepared by reduction of silver ions in N₂H₅OH aqueous solution. The Ag/PAN nanocomposite film was characterized by UV absorption spectroscopy, transmission electron microscopy (TEM) and surface-enhanced Raman scattering (SERS) spectroscopy. UV spectrum and TEM image show that silver nanoparticles with average diameter of 10 nm were obtained and dispersed homogeneously in PAN nanofibers. SERS spectrum indicates that the structure of PAN has been changed after Ag nanoparticles are dispersed in PAN.     

Nanogap Engineered Plasmon‐Enhancement in Photocatalytic Solar Hydrogen Conversion

Graphitic carbon nitride modified with plasmonic Ag@SiO₂ core–shell nanoparticles (g‐C₃N₄/Ag@SiO₂) are proposed for enhanced photocatalytic solar hydrogen evolution under visible light. Nanosized gaps between the plasmonic Ag nanoparticles (NPs) and g‐C₃N₄ are created and precisely modulated to be 8, 12, 17, and 21 nm by coating SiO₂ shells on the Ag NPs. The optimized photocatalytic hydrogen production activity for g‐C₃N₄/Ag@SiO₂ is achieved with a nanogap of 12 nm (11.4 μmol h⁻¹) to be more than twice as high as that of pure g‐C₃N₄ (5.6 μmol h⁻¹). The plasmon resonance energy transfer (PRET) effect of Ag NPs is innovatively proved from a physical view on polymer semiconductors for photoredox catalysis. The PRET effect favors the charge carrier separation by inducing electron–hole pairs efficiently formed in the near‐surface region of g‐C₃N₄. Furthermore, via engineering the width of the nanogap, the PRET and energy‐loss Förster resonance energy transfer processes are perfectly balanced, resulting in considerable enhancement of photocatalytic hydrogen production activity over the g‐C₃N₄/Ag@SiO₂ plasmonic photocatalyst.     

Nearly perfect (001)-oriented Ag/[CoPt/C]5/Ag composite films deposited on glass substrates

Sandwich Ag/[CoPt(3 nm)/C(3 nm)]₅/Ag films were deposited on glass substrates by magnetron sputtering. After annealing at 600 °C for 30 min, a nearly-perfect (001)-oriented L1₀ CoPt film with extremely high perpendicular anisotropy was obtained when the thickness of Ag top- and underlayer were both equal to 5 nm. The strain energy caused by the Ag layer together with the diffusion of Ag and C atoms, resulted in the enhancement of the ordering degree of the L1₀ CoPt phase and the development of the (001) texture of the films.     

Solvothermal synthesis of the special shape (deformable) hollow g-C3N4 nanospheres

Special shaped (deformable) hollow g-C₃N₄ nanospheres were synthesized by the solvothermal technique using silica spheres as template. The X-ray diffraction (XRD) peaks of the product were indexed to g-C₃N₄ materials. Field-Emission Scanning Electron Microscopy and Transmission Electron Microscopy confirmed that the external diameter of the hollow nanospheres is about 130-150 nm and thickness of the wall is about 20-30 nm. The FTIR spectrum showed absorption peak at 810 cm^-1 can be attributed to the s-triazine (C₃N₃) breathing mode. Raman spectrum exhibited two broad peaks approximately at 1360 cm^-1 (D band) and 1580 cm^-1 (G band). The deformed pie shape or mortars like hollow spheres were first reported. The flexility of the deformable hollow g-C₃N₄ nanospheres may be used in special field such as drug delivery carriers adjusting the delivery ratio by the external pressure, and a good material for studying the mechanical properties of the sp² hybrid g-C₃N₄. The photoluminescence spectrum of the product indicates that the deformable hollow g-C₃N₄ nanospheres may have potential applications in nano-optical device fields.     

Transmission electron microscope study of the topotactic reaction of (0 0 1), (0 1 1) and (1 1 1) Ag films and Te

The formation, structure and morphology of silver telluride was investigated in the reaction of (0 0 1), (0 1 1) and (1 1 1) single crystalline Ag films with vacuum deposited Te. Silver films 30–40 nm in thickness were deposited by thermal evaporation onto water- and chlorine-treated NaCl. Onto this silver 1–40 nm of tellurium were deposited at 100 and 200 °C. The Ag–Te reaction occurred during Te deposition. Accordingly, formation of the compound phase was investigated from the nucleation stage through complete tellurization on either side of the polymorphic phase transformation temperature (T_c=150 °C). Transmission electron microscope and selected area electron diffraction showed that monoclinic silver telluride (Ag₂Te) of different morphology and texture was always formed. The orientation of silver and monoclinic phase upon differently oriented monocrystalline Ag films and at deposition temperatures around T_c is discussed.     

Silvering of magnesium by contact deposition in aqueous solutions and DMFA medium

We study the deposition of thin silver films onto a magnesium surface in aqueous solutions of silver complexes and in organic aprotic solvents. We show that compact silver films with good adhesion are deposited in aqueous solutions of [Ag(CN)₂]⁻ cyanocomplex under hydrodynamic conditions. In solutions of less stable complexes {thiocyanate [Ag(CNS)₄]³⁻ and thiocarbamide [Ag(thio)₄]⁺}, the contact deposition of only disperse silver is observed. In dimethylformamide solutions of [Ag(CNS)₄]³⁻ complexes, thin silver films with good adhesion to a magnesium surface are formed. We also describe some specific features of the morphology of silver deposits, formed on a magnesium surface. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 42, No. 5, pp. 95–97, September–October, 2006.