Silver Nanoparticle Arrays Research Articles

Bideposited silver nanocolloid arrays with strong plasmon-induced birefringence for SERS application

Silver nano-rod, nano-zigzag, nano-saw, and nano-particle arrays are fabricated with glancing angle bideposition. The structure-dependent anisotropic optical properties of those bideposited nanostructured arrays are measured and investigated. The equivalent birefringence values of nano-rod and nano-zigzag arrays are much larger than crystals found in nature and liquid crystal used in display products. The fact that induced localized plasmon-magnetic field between nanorods dominates the strong phase retardation between p-polarized and s-polarized transmitted wave. For the nano-saw, the strong localized electric field induced between the saw teeth leads to strong SERS signals. Although the bideposited nanoparticles own weak morphological anisotropy, strong optical phase retardation is still detected at wavelengths near 400 nm.

Gas aggregated Ag nanoparticles as the inorganic matrix for laser desorption/ionization mass spectrometry

We report here on a nanoparticle-assisted laser desorption/ionization time-of-flight mass spectrometry (NP-LDI-TOF MS) for the detection of small molecules. This technique is based on the overcoating of a dried analyte by an array of silver nanoparticles produced by gas aggregation source. This allows for the spatially homogeneous distribution of nanoparticles over the analyte that may fully substitute a conventional organic matrix routinely used for the matrix-assisted laser desorption/ionization mass spectrometry and thus limit the possible interference of matrix with the low-mass molecules. Furthermore, it is shown that the intensity of the detected signal strongly correlates with the number of deposited Ag nanoparticles. At its optimum, that was found to correspond to the nanoparticle surface density of 3x103 NPs.µm−2, the detection limit was 3x10-8 g.L-1 for riboflavin. Such a high detection limit, together with good reproducibility, excellent signal stability, and imaging capability, makes this technique a valuable alternative to other laser desorption/ionization-based detection methods.

Comparison of hot carrier generation between self-assembled gold and silver nanoparticle arrays tailored to the same hybrid plasmon resonance

We evaluated the properties of hot carrier generation on Au and Ag nanoparticle (NP) 2D arrays by monitoring chemical transformation. The arrays were fabricated by assembling the Au and AgNPs, respectively, with a diameter of ∼30 nm. The plasmon resonance peaks of both the arrays were tuned to around 671 nm, where the intraband transition was the dominant pathway for the surface plasmon excitation since the incident photon energy is below the interband transition threshold for both Au and Ag. Time-resolved surface-enhanced Raman scattering (SERS) spectroscopy was utilized to monitor the changes in the molecular structure sensitively. We selected para-aminothiophenol as the molecule, which was well known to transform to 4,4′-dimercaptoazobenzene (DMAB) by hot carriers generated from the plasmonic excited surface. It was observed that the peak intensity of DMAB increased as the total exposure increased due to the increase in the number of DMAB molecules for both metals, similar to our previous reports. The analysis of the SERS spectra showed that larger laser intensity progressed the transformation more rapidly. The analysis also clarified that the chemical transformation occurs more efficiently on the AgNP array compared to the AuNP array. The superiority in the efficiency for Ag may be derived from contribution of more hot carriers generated in the material with the smaller plasmon damping constant.

Rapid identification of nicotine in electronic cigarette liquids based on surface-enhanced Raman scattering.

Nicotine-containing electronic cigarette liquid (e-liquid) is prohibited in many countries, creating requirements for rapid detection approaches for on-site inspection or screening for large amounts of samples. Here, we demonstrate a simple way to identify nicotine using surface-enhanced Raman scattering (SERS) with substrates made of silver nanoparticle arrays imbedded in anodic aluminum oxide nanochannels (Ag/AAO). Compared with the reported colloidal nanoparticle-based SERS, that required serial dilutions to enable colloid aggregation in the viscous e-liquid, a small amount of undiluted e-liquid sample can be directly added onto our solid-phase Ag/AAO substrate without any pre-treatment. The sensitivity of our SERS measurements is 2–3 orders of magnitude higher than that required for identification of nicotine in e-liquid, which is typically around 1000–18,000 ppm. Using such nanoparticle array-based SERS, we have tested 22 commercially available e-liquid products, using the corresponding gas chromatography-mass spectrometry (GC–MS) reports as the reference. The SERS measurements were done within one hour and successfully identified 20 samples. Only 2 samples showed SERS interference from ingredients that were not suitable for SERS analysis.

Surface-Enhanced Raman Spectroscopy for Trace Detection of Tetracycline and Dicyandiamide in Milk Using Transparent Substrate of Ag Nanoparticle Arrays

Tetracycline (TC) is an antibiotic utilized in dairy livestock, which can leave trace residues in milk and other dairy products. Dicyandiamide (DCD), a grassland fertilizer, but also potentially an adulterant to increase milk apparent protein content, has been found in milk products that were subsequently banned. Both these chemicals can pose human health risks via the consumption of dairy foods, and therefore rapid, simple detection methodologies are necessary. Herein, we fabricated a transparent and homogeneous substrate by fabricating silver nanoparticle (Ag NP) arrays based on the anodic aluminum oxide (AAO) template-assisted electrochemical deposition approach. The periodic nanostructure was optimized to obtain high SERS activity by varying nanopore diameters and Ag NP sputtering duration to have Ag NP nanogaps in the sub 10 nm regime so that the high sensitivity was achieved with detecting R6G analytes at the 1 × 10–10 M level. The substrate was also used to detect TC and DCD in milk at low concentration levels of 1 × 10–9 M and 1 × 10–7 M, respectively, with good linear correlation between concentration and intensity (TC R2 = 0.96; DCD R2 = 0.99). The assignments of Raman bands of tetracycline and dicyandiamide were also given by density-functional-theory (DFT) calculations. The advantage of this transparent SERS substrate is that it is especially useful for measurement of analytes at the interface between Ag NP substrate layer and the opaque liquid containing the analytes without special pretreatment of the sample. Thus, this method may provide an alternative practical and reliable platform for rapid detection of contaminants in foods.

Hot Carrier Generation in Two-Dimensional Silver Nanoparticle Arrays at Different Excitation Wavelengths under On-Resonant Conditions

We evaluated the hot carrier generation in two-dimensional (2D) silver nanoparticle (AgNP) arrays under light illumination at different wavelengths, 458, 532, 671, and 785 nm. The 2D AgNP arrays we...

Strongly Coupled Exciton-Surface Lattice Resonances Engineer Long-Range Energy Propagation.

Achieving propagation lengths in hybrid plasmonic systems beyond typical values of tens of micrometers is important for quantum plasmonics applications. We report long-range optical energy propagation due to excitons in semiconductor quantum dots (SQDs) being strongly coupled to surface lattice resonance (SLRs) in silver nanoparticle arrays. Photoluminescence (PL) measurements provide evidence of an exciton-SLR (ESLR) mode extending at least 600 μm from the excitation region. We also observe additional energy propagation with range well beyond the ESLR mode and with dependency on the coupling strength, g, between SQDs and SLR. Cavity quantum electrodynamics calculations capture the nature of the PL spectra for consistent g values, while coupled dipole calculations show a SQD number-dependent electric field decay profile consistent with the experimental spatial PL profile. Our results suggest an exciting direction wherein SLRs mediate long-range interactions between SQDs, having possible applications in optoelectronics, sensing, and quantum information science.

Molecular-Level Control over Plasmonic Properties in Silver Nanoparticle/Self-Assembling Peptide Hybrids.

The plasmonic properties of silver nanoparticle (AgNP) arrays are directly controlled by AgNP size, shape, and spatial arrangement. Reported here is a strategy to prepare chiral AgNP arrays templated by two constitutionally isomeric aromatic peptide amphiphiles (APAs), KSC'EKS and C'EKSKS (KS = S-aroylthiooxime-modified lysine, C' = citrulline, and E = glutamic acid). In phosphate buffer, both APAs initially self-assembled into nanoribbons with a similar geometry. However, in the presence of silver ions and poly(sodium 4-styrenesulfonate) (PSSS), one of the nanoribbons (KSC'EKS) turned into nanohelices with a regular twisting pitch, while the other (C'EKSKS) remained as nanoribbons. Both were used as templates for synthesis of arrays of ∼8 nm AgNPs to understand how small changes in molecular structure affect the plasmonic properties of these chiral AgNP/APA hybrids. Both hybrids showed improved colloidal stability compared to pure AgNPs, and both showed enhanced sensitivity as surface-enhanced Raman spectroscopy (SERS) substrates for model analytes, with nanohelices showing better SERS performance compared to their nanoribbon counterparts and pure AgNPs.

Resonant Optical Phenomena in Heterogeneous Plasmon Nanostructures of Noble Metals: A Review

The interaction of electromagnetic radiation with ordered and disordered arrays of noble metal nanoparticles, leading to the excitation of various modes of surface plasmon states in them, is analyzed. The dipole localized surface plasmon resonance in isolated nanoparticles and the influence of various size effects on its optical response are considered. The effect of dipole-dipole interaction between gold and silver nanoparticles on the optical properties of various nanosized and nanostructured objects is discussed. It is shown that both localized and delocalized (propagated) surface plasmon modes can be excited in composite gold and silver nanosystems, in particular, in porous films. The prospects for the practical application of nanostructures with arrays of gold and silver nanoparticles in sensor technology, surface-enhanced Raman spectroscopy, and modern optoelectronics are examined.

Enhancement of localized surface plasmon resonances of silver nanoparticles array upon the presence of graphene coatings: LSPR biosensor

We study, in this article, the resonance of localized surface plasmon (LSPR) on silver nanoparticles (AgNPs) deposited on a glass substrate and coated with a graphene. The resonance peaks in the absorption spectra of the nanostructure SiOx/AgNPs/Graphene, show significantly different profiles such as the thickness of the graphene, and the refractive index of the surrounding environment which is, gradually, varied. Numerical simulation reveals that movements in plasmon resonance peaks result from coupling between the AgNPs networks and the covering graphene layer. In addition, the LSPR modes shift to red from 412 nm to 548 nm when the thickness of the graphene layer deposited on silver nanoparticles changes from 0.34 nm to 9 nm. Light coupled with LSPR modes propagating along a AgNPs-graphene interface is calculated and compared to a conventional AgNPs-based LSPR biosensor. The result of the comparison depicts an improvement in the sensitivity of the biosensor from 26 to 106 nm/RIU.

Colorimetric aggregation assay based on array of gold and silver nanoparticles for simultaneous analysis of aflatoxins, ochratoxin and zearalenone by using chemometric analysis and paper based analytical devices.

A paper based sensor array ispresented to discriminate and determine five mycotoxins classified into three categories, namely aflatoxins, ochratoxins and zearalenone. The gold and silver nanoparticles, synthesized by three different reducing or capping agents, were employed as sensing elements of thefabricated device. These nanoparticles were poured onto hydrophilic circular zones embedded on the hydrophobic substrate. The response of the assay is dependent on the aggregation of nanoparticles for interaction with mycotoxins. Due to aggregation, the gold and silver nanoparticles changed to purple and brown, respectively. Color changes provide unique colorimetric signatures conducive to recognizing the type of mycotoxin, identifying its chemical structure, and finding the fungi that produce it. The discrimination ability of the assay was investigated by both supervised (linear discriminate analysis) and unsupervised (principle component analysis and hierarchical cluster analysis) pattern recognition methods. The assay was applied to the point of need determination of aflatoxin B1, aflatoxin G1, aflatoxin M1, ochratoxin A and zearalenone with a detection limit of 2.7, 7.3, 2.1, 3.3 and 7.0ng.mL-1, respectively. The fabricated device has highpotential of simultaneously determining the mycotoxins in pistachio, wheat, coffee and milk with the help of partial least square method. The root mean square errors for prediction of PLS model were 5.7, 5.2, 1.5, 7.2 and 2.9 for aflatoxin B1, aflatoxin G1, aflatoxin M1, ochratoxin A and zearalenone, respectively. Graphical abstractSchematic representation of paper based colorimetric sensor array based on gold and silver nanoparticles for both qualitative and quantitative analysis of aflatoxins, ochratoxin and zearalenone.

Fabrication of uniform arrays of silver nanoparticles on silicon by electrodeposition in ethanol solution and their use in SERS detection of difenoconazole pesticide.

Surface-Enhanced Raman Scattering (SERS) is a technique currently widely used in the identification and quantification of organic and biological molecules at low concentrations, in which an important application is the detection of pesticide residues in food. To accomplish this task, SERS substrates with high Raman enhancement factor and good reproducibility are required. One of the most commonly used SERS substrates is the SERS substrate made of silver nanoparticles immobilized on a solid substrate. In this report we first present the results of electrochemical deposition of silver nanoparticles on the silicon surface using ethanol electrolyte solution. Thanks to both factors, electrochemical deposition (instead of electroless) and ethanol electrolyte (instead of aqueous), under optimal conditions, on the surface of silicon a monolayer of silver nanoparticles grew, which are uniform in shape and size and are arranged very close to each other with nanometer separation. Next we report on the use of fabricated arrays of silver nanoparticles in the role of a SERS substrate. To test the performance of the SERS substrate, the probe molecules used were molecules of difenoconazole, a well-known fungicide. Results showed that difenoconazole could be detected with a detection limit of 0.023 ppm (5.6 × 10−8 M).

The Influence of Laser Sintering Modes on the Conductivity and Microstructure of Silver Nanoparticle Arrays Formed by Dry Aerosol Printing

The demand for the development of local laser sintering of nanoparticle arrays is explained by the expanding needs for printed electronics for functional microstructure formation, on heat-sensitive substrates in particular. This work is based on the research into the sintering of arrays of silver nanoparticles synthesized in a spark discharge and deposited on a substrate by focused aerosol flow. The sintering was done by continuous and pulsed lasers with wavelengths 527, 980 and 1054 nm. Sintered samples were studied by measuring the resistivity, cross-section profile area and microstructure features. The highest average conductivity, equal to the half of the bulk silver conductivity, was achieved when sintering by continuous radiation with a wavelength 980 nm. The results showed that when using pulsed radiation the direct heating of nanoparticles in the sample surface layer dominates with the formation of a pore-free conductive layer of around 0.5 μm thick and crystallite of 70–80 nm size. It was found that laser sintering by radiation with a wavelength 527 nm required an order of magnitude lower specific energy costs as compared to the longwave laser radiation. The high energy efficiency of laser sintering is explained by special conditions for radiation absorption at plasmon resonance.

Dielectric tensor of a rectangular arrangement of Ag nanoparticles in anisotropic [formula omitted]: Analysis of the negative epsilon conditions

In the present paper we report the optical response of an ordered array of silver (Ag) nanoparticles (NPs) using the uniaxial LiNbO3 as a model case. We investigate the anisotropic effects on the effective dielectric tensor taking into account the charges interaction of particles. The Ag NPs dielectric function is described through a modified Drude model whereas the LiNbO3 dielectric functions are deduced from their experimentally established Sellmeier equations. The effective dielectric tensor components of the ensemble aggregates of Ag NPs and uniaxial LiNbO3 crystal are treated through the extended Maxwell–Garnett approximation. Following the asymmetric behaviour of uniaxial crystals, Ag NPs are sited in the ordinary plane of the crystal, giving rise to different responses in the x, y and z directions of applied electric field. Real and imaginary parts of the effective dielectric tensor components of the aggregate ensemble are investigated in terms of different structural parameters, such as the interparticle spacings, the NPs filling factor and sizes of spherically embedded nanoparticles. We demonstrate that an adequate choice of structural parameters such as NPs sizes, interparticle separation gaps or the filling factor can determine the optical properties of layered Ag–embedded uniaxial crystals such as LiNbO3. We show that the negative epsilon (NE) condition is satisfied from a critical size of Ag NPs when the filling factor and the interparticles distances (a and b) have particular values. This condition defines an interval of energies, called NE range, which clearly depend on values of structural parameters defined in the model. This NE range shows some type of bandwidth anisotropy when it is compared among the x-, y-, z- and xy-components of the effective dielectric tensor. We analyze some anisotropic features such as the bandwidth and shift resonance energies in the real and imaginary parts of the dielectric tensor when structural parameters change.

Термическая стабилизация геометрических параметров массива наночастиц серебра, полученного вакуум-термическим испарением на ненагретую подложку

Термическая стабилизация геометрических параметров массива наночастиц серебра, полученного вакуум-термическим испарением на ненагретую подложку

Laser sintering of silver nanoparticles deposited by dry aerosol printing

This work is devoted to the sintering of silver nanoparticle arrays in the form of lines by the local treatment with laser radiation with wavelengths of 527, 1054 and 1064 nm in pulsed and continuous laser modes. The silver nanoparticle lines were formed by the dry aerosol printing, free from organic solvents and surfactants. To form the lines with a width of 25–300 μm and a thickness of 0.1–15 μm a focused stream of nanoparticles with an average size of about 60 nm was used. It is shown that when using continuous laser radiation with a wavelength of 1064 nm, the minimal specific resistance of silver nanoparticle lines was achieved 3 times higher than that for the bulk material was reached.

Nanostructures based on functionalized porous silicon for promising solar energy systems

The promising application of functionalized composite materials based on porous silicon (PS) for perspective solar energy conversion systems is considered in this paper. PS-based nanostructures are suggested for further realization of photon-enhanced thermionic emission for solar concentrators and thermionic electrodes due to the remarkable properties displayed by these materials. Nanostructured layers functionalized with silver (PS/Ag) are obtained via electrochemical etching and deposition processes. The investigation of acquired materials functionalized with fractal-like silver agglomerates is performed. Electronic absorption spectroscopy is utilized in order to characterize the surface structure of PS/Ag layers. Localized surface plasmon resonance phenomenon taking place within the array of silver nanoparticles is observed. Two distinct absorption bands located in the visible spectrum are detected; their emergence is related to the resonance effect taking place in the two nanoparticle arrays appearing during the synthesis process. The intensity of these bands can be manipulated with synthesis parameters of porous silicon matrix.

Photoelectrochemical response of Ag-graphene heterostructures: insight into the localized surface plasmon enhanced photocurrent generation process

We present Ag-graphene heterostructures by combining few layer graphene (FLG) with plasmonic silver nanoparticle (AgNP) arrays to boost the photoelectrochemical (PEC) efficiency of graphene-based nanostructures. AgNP arrays with controlled coverage and size distribution were fabricated on the graphene surface by means of gas phase cluster beam deposition. The photocurrent generation process in the FLG-based nanostructures was analyzed with a PEC amperometric measurement. A significant photocurrent enhancement was observed in the AgNPs-FLG heterostructures compared with bare FLG. It was found that the PEC performance was strongly related to the wavelength and power of the incident light, as well as the density and size of the AgNPs. The enhancement of the PEC response was attributed to the effect of the surface plasmon local fields of the AgNPs, which induce efficient generation and quick separation of the electron–hole pairs in FLG.

Design and analysis of thin film GaAs solar cells using silver nanoparticle plasmons

In this paper, we present a design and analysis of thin film GaAs solar cells using silver nanoparticle array. In the front surface design of GaAs solar cells, we assembled silver nanoparticle array on the top of quarter wavelength antireflection layers. For rear surface design, a reflection layer structure is designed using surface plasmon effects induced by the silver nanoparticle array. The transmittance of light for front and rear surfaces is monitored by using finite difference time domain (FDTD) method in the wavelength range of 400–900 nm. The simulation results confirm that the utilization of light within solar cells may be increased by optimizing the structural parameters associated with silver nanoparticle array. This analysis also revealed that grating characteristics of silver nanoparticle array and surface plasmon effects induced by silver nanoparticles play important roles for effective design of GaAs solar cells.

Excitation of Bloch surface wave using silver nanoparticles for sensitivity enhanced biosensor

A silver nanoparticles array is introduced on the top layer of all-porous-silicon refractive index sensor. Bloch surface wave (BSW) resonance is realized at the interface between air and multilayer porous silicon structure, which can be excited by different coupling schemes: the Kretschmann prism and silver nanoparticles array. In addition to sustaining the BSW mode, the silver nanoparticles add an additional degree of freedom to the phase-matching conditions. We demonstrated the sharp BSW reflectivity dip with an ultra-narrow linewidth. The performance of the designed BSW sensor is numerically calculated by the rigorous coupled wave analysis (RCWA) method under s-polarized light. The optimized silver nanoparticles coupled BSW (AgNPs-BSW) sensor has a much higher figure of merit () than conventional prism-coupled BSW sensors. The azimuthal sensitivity can reach about 703°/RIU or even higher. The proposed silver nanoparticles coupled BSW (AgNPs-BSW) sensor exhibits the capacity to eliminate the adverse effects of inhomogeneous penetration of analytes. With such excellent performance, our study demonstrates its potential applications in the field of chemical and biological sensors in the future.