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.     

Preparation of silver nanoparticles by photo-reduction for surface-enhanced Raman scattering

A substrate for surface-enhanced Raman scattering (SERS) has been developed. Based on the surface-catalyzed reduction of Ag⁺ by citrate on the silver nanoparticles surface under light irradiation, small silver seeds on a quartz slide can be enlarged. The optical properties and characteristics of the silver films have been investigated by ultraviolet-visible spectroscopy, scan electron microscope and atomic force microscopy (AFM). The results indicate that the particle size and shape are different at different reduction time. At the first 3 h, some triangular and hexagonal nanoparticles formed; with the reduction proceeding, the shape of the silver particles became irregular and the size became larger. The silver films obtained are very suitable as SERS active substrate. The relationship between SERS intensity and the reduction time has been investigated for 1,4-bis[2-(4-pyridyl)ethenyl]-benzene molecule adsorbed on the silver film. The SERS intensity reached a maximum at 8 h reduction. The AFM measurements indicate that roughness features with an average size of 100 nm are present on the surface, which yielded the strongest SERS signal. Pyridine was used as a probe molecule to investigate the enhancement factor (EF) of the silver films. According to the formalism of Tian and co-workers, the EF of the silver films is estimated to be 3.4 × 10⁵. The silver film that can remain active for more than 50 days would seem to be suitable for various analytical applications.     

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.     

New pathway to prepare surface-enhanced Raman scattering-active silver nanoparticles based on electrochemical methods

In this work, we report a new strategy to prepare silver (Ag) nanoparticles (NPs) from bulk Ag substrates. First, positively charged Ag ions were prepared by electrochemical methods in 0.1 N HNO₃ aqueous solutions. Then the solutions were heated from room temperature to 100 °C at a heating rate of 6 °C/min to prepare Ag nanoparticles. The average particle size of the prepared Ag NPs with predominant (111) face is ca. 10 nm. Experimental results indicate that the prepared Ag (111) nanoparticles in solutions are surface-enhanced Raman scattering (SERS)-active, which are examined by probe molecules of Rhodamine 6G.     

SERS effects in silver-decorated cylindrical nanopores

Optimization of pore diameter, the placement of nanoparticles, and the transmission of surface-enhanced Raman scattering (SERS) substrates are found to be very critical for achieving high SERS activity in porous alumina-membrane-based substrates. SERS substrates with a pore diameter of 355 nm incorporating silver nanoparticles show very high SERS activity with enhancement factors of 10(10) .     

High-density silver nanoparticle film with temperature-controllable interparticle spacing for a tunable surface enhanced Raman scattering substrate

The formation of high-density silver nanoparticles and a novel method to precisely control the spacing between nanoparticles by temperature are demonstrated for a tunable surface enhanced Raman scattering substrates. The high-density nanoparticle thin film is accomplished by self-assembling through the Langmuir-Blodgett (LB) technique on a water surface and transferring the particle monolayer to a temperature-responsive polymer membrane. The temperature-responsive polymer membrane allows producing a dynamic surface enhanced Raman scattering substrate. The plasmon peak of the silver nanoparticle film red shifts up to 110 nm with increasing temperature. The high-density particle film serves as an excellent substrate for surface-enhanced Raman spectroscopy (SERS), and the scattering signal enhancement factor can be dynamically tuned by the thermally activated SERS substrate. The SERS spectra of Rhodamine 6G on a high-density silver particle film at various temperatures is characterized to demonstrate the tunable plasmon coupling between high-density nanoparticles.     

Novel method for preparing controllable and stable silver particle films for surface-enhanced Raman scattering spectroscopy

A new surface-enhanced Raman scattering (SERS) active substrate has been developed based on our previous study. Small silver nanoparticles on a quartz slide can be enlarged by using a mixture of commercially available reagents called Silver Enhancer and Initiator. The optical properties and characteristics of the new substrate have been investigated by ultraviolet-visible (UV-Vis) spectroscopy and atomic force microscopy (AFM). The results indicate that the small silver nanoparticles grow and some silver aggregates emerge on the quartz slide after the slide is immersed into the Silver Enhancer and Initiator Mixture (SEIM). The average diameter of the silver nanoparticles on the substrate becomes approximately double after the immersion into SEIM for 20 s. 1,4-bis[2-(4-pyridyl)ethenyl]-benzene (BPENB) was used as a Raman probe to evaluate the enhancement ability of the new silver substrate. It has been found that the SERS intensity can be increased about 10 times by using the substrate treated by SEIM compared with that without being treated by SEIM. Interestingly enough, the SERS enhancement increases with time. This may be due to the reorganization of silver nanoparticles on the quartz surface. The new substrate can remain active for more than 90 days. The adsorption mode of BPENB on the new substrate and the dependence of the BPENB configurations on the concentration of BPENB in methanol solution have also been investigated by SERS or UV-Vis spectroscopy. The SERS spectra of a self-assembled monolayer (SAM) BPENB film adsorbed on a silver substrate treated by SEIM show that BPENB molecules are chemically absorbed through the Ag-N bond. Consequently, a nearly perpendicular orientation of BPENB on the silver surface is proposed. The SERS spectra of BPENB SAMs on the new substrates fabricated from methanol solutions with different concentrations are compared. The concentration dependence of the SERS spectra reveals that the BPENB molecules are adsorbed on the silver film as monomers when the film is prepared from the solution with a lower concentration (<4 x 10(-6) M) and as aggregates when it is prepared from the solution with a higher concentration (>1 x 10(-5) M).     

In situ growth of silver nanoparticles in porous membranes for surface-enhanced raman scattering

We demonstrate the in situ growth of silver nanoparticles in porous alumina membranes (PAMs) for use as a surface-enhanced Raman scattering (SERS) detection substrate. This fabrication method is simple, cost-effective, and fast, while providing control over the size of silver nanoparticles through the entire length of the cylindrical nanopores with uniform particle density inside the pores unachievable by the traditional infiltration technique. The in situ growth of silver nanoparticles was conducted from electroless-deposited nanoscale seeds on the interior of the PAM and resulted in the formation of numerous hot spots, which facilitated significantly higher SERS enhancement for these substrates compared with previously reported porous substrates.     

A novel method for fabricating the surface-enhanced Raman scattering substrates and its enhanced properties

We have got large area surface-enhanced Raman scattering (SERS) substrates with uniform high enhancement factors by the so-called moulage method for the first time. A silver film (99.99%) with several millimeters thickness was thermally evaporated on the porous anodic alumina templates and the SERS substrate was got after moving off the templates. Surface-enhanced Raman scattering spectra of pyridine (0.01 Mol/L) were measured under 632.8 nm excitation. The experimental enhancement factors were more than 10(5) and S/N(p-p) around 100 was obtained. We have compared the SERS spectra of pyridine collected from different locations on the same SERS substrate and different substrates, which illustrate the well uniform enhance properties and the reproducibility of this method, respectively. The comparison of the SERS spectra, obtained from the SERS substrates and Ag film evaporated directly on glass slide, have proved that the electromagnetic coupling between two adjacent nanoparticles was important to the SERS effect. We also used rhodamine 6G as the probe molecules and found that the different molecules were very sensitive to the morphology of the SERS substrates.     

High Surface‐Enhanced Raman Scattering Performance of Individual Gold Nanoflowers and Their Application in Live Cell Imaging

Molecular imaging techniques based on surface‐enhanced Raman scattering (SERS) face a lack of reproducibility and reliability, thus hampering its practical application. Flower‐like gold nanoparticles have strong SERS enhancement performance due to having plenty of hot‐spots on their surfaces, and this enhancement is not dependent on the aggregation of the particles. These features make this kind of particle an ideal SERS substrate to improve the reproducibility in SERS imaging. Here, the SERS properties of individual flower‐like gold nanoparticles are systematically investigated. The measurements reveal that the enhancement of a single gold nanoparticle is independent of the polarization of the excitation laser with an enhancement factor as high as 10⁸. After capping with Raman signal molecules and folic acid, the gold nanoflowers show strong Raman signal in the living cells, excellent targeting properties, and a high signal‐to‐noise ratio for SERS imaging.     

Surface-enhanced Raman scattering dendritic substrates fabricated by deposition of gold and silver on silicon

This paper reports a study on the preparation of gold nanoparticles and silver dendrites on silicon substrates by immersion plating. Firstly, gold was deposited onto silicon wafer from HF aqueous solution containing HAuCl4. Then, the silicon wafer deposited gold was dipped into HF aqueous solution of AgNO3 to form silver coating gold film. Scanning electron microscopy reveals a uniform gold film consisted of gold nanoparticles and rough silver coating gold film containing uniform dendritic structures on silicon surface. By SERS (surface-enhanced Raman scattering) measurements, the fabricated gold and silver coating gold substrates activity toward SERS is assessed. The SERS spectra of crystal violet on the fabricated substrates reflect the different SERS activities on gold nanoparticles film and silver coating gold dendrites film. Compared with pure gold film on silicon, the film of silver coating gold dendrites film significantly increased the SERS intensity. As the fabrication process is very simple, cost-effective and reproducible, and the fabricated silver coating gold substrate is of excellent enhancement ability, spatial uniformity and good stability.     

Raman scattering and Rutherford backscattering studies on InN films grown by plasma-assisted molecular beam epitaxy

A series of InN thin films was grown on sapphire substrates via plasma-assisted molecular beam epitaxy (PA-MBE) with different nitrogen plasma power. Various characterization techniques, including Hall, photoluminescence, Raman scattering and Rutherford backscattering, have been employed to study these InN films. Good crystalline wurtzite structures have been identified for all PA-MBE grown InN films on sapphire substrate, which have narrower XRD wurtzite (0002) peaks, showed c-axis Raman scattering allowed longitudinal optical (LO) modes of A₁ and E₁ plus E₂ symmetry, and very weak backscattering forbidden transverse optical (TO) modes. The lower plasma power can lead to the lower carrier concentration, to have the InN film close to intrinsic material with the PL emission below 0.70 eV. With increasing the plasma power, high carrier concentration beyond 1 × 10²⁰ cm^− 3 can be obtained, keeping good crystalline perfection. Rutherford backscattering confirmed most of InN films keeping stoichiometrical In/N ratios and only with higher plasma power of 400 W leaded to obvious surface effect and interdiffusion between the substrate and InN film.     

Improved SERS Intensity from Silver‐Coated Black Silicon by Tuning Surface Plasmons

An economical method of fabricating large‐area (up to a 100‐mm wafer) silver (Ag)‐coated black silicon (BS) substrates is demonstrated by cryogenic deep reactive ion etching with inductively coupled plasma. This method enables a simple adjustment of the spike structure (e.g., height, width, sidewall slope and density of the spikes) on the silicon substrate, which thus offers the advantages of accurate tuning the density and amplitude of the localized surface plasmons after Ag coating. Using this method, an enhancement factor of 10⁹ is achieved for the probe molecule of rhodamine 6G (around two orders of magnitude higher than previous results based on Ag‐coated BS) in surface‐enhanced Raman scattering (SERS) measurement. The presented results pave the way to make Ag‐coated BS substrates as economic and large‐area platforms for diverse surface plasmon related applications (such as SERS and surface plasmon based biosensors).     

Silver nanoclusters films for single molecule detection using Surface Enhanced Raman Scattering (SERS)

A highly efficient Surface Enhanced Raman Scattering (SERS) substrate was prepared using a nanocluster deposition system that enabled detection of Crystal Violet molecules down to a single molecule level. The large SERS signal enhancement can be attributed to the presence of nano gaps on the surface of the nanoclusters which create abundant hot spots for electric field enhancement. Observed variations in the Raman peaks at very low molar concentrations in the range 4 × 10⁻¹⁴–3.2 × 10⁻¹⁸ M suggest that the spectra are due to a single molecule. Possible mechanisms for ultrahigh SERS sensitivity of the substrates are discussed. These substrates take the detection limit of CV down by two orders of magnitude as compared to those reported in literature.     

负载银簇的硅基杂化纳米颗粒制备及其SERS性能

本研究发展了一种简便的"原位还原"策略构建负载银簇的硅基杂化纳米颗粒(Ag@SHNPs)。首先利用两亲性嵌段共聚物PS₈₉-b-PAA₁₆自组装行为和3-巯基丙基三甲氧基硅烷(MPTMS)在亲水链段PAA区域的水解缩聚反应形成有机硅胶束杂化纳米结构,再利用有机硅骨架中丰富的巯基作为还原位点,原位将银盐转化为银簇,最终得到负载银簇的硅基杂化纳米颗粒,并对该杂化纳米颗粒的形貌、结构以及成分组成作了分析。通过测试材料对不同细胞系的毒性验证了其良好的生物相容性。最后以4-巯基苯甲酸(4-MBA)为探针分子,对硅基杂化颗粒基底的表面增强拉曼散射(SERS)活性进行检测。在532 nm波长的激光激发下, 4-MBA标记的硅基杂化纳米颗粒展示出明显的拉曼信号增强特性,增强因子约为10⁵。因此,该硅基杂化基底材料在SERS生物成像和高灵敏检测方面具有潜在的应用前景。     

Pen‐on‐Paper Approach Toward the Design of Universal Surface Enhanced Raman Scattering Substrates

The translation of a technology from the laboratory into the real world should meet the demand of economic viability and operational simplicity. Inspired by recent advances in conductive ink pens for electronic devices on paper, we present a “pen‐on‐paper” approach for making surface enhanced Raman scattering (SERS) substrates. Through this approach, no professional training is required to create SERS arrays on paper using an ordinary fountain pen filled with plasmonic inks comprising metal nanoparticles of arbitrary shape and size. We demonstrate the use of plasmonic inks made of gold nanospheres, silver nanospheres and gold nanorods, to write SERS arrays that can be used with various excitation wavelengths. The strong SERS activity of these features allowed us to reach detection limits down to 10 attomoles of dye molecules in a sample volume of 10 μL, depending on the excitation wavelength, dye molecule and type of nanoparticles. Furthermore, such simple substrates were applied to pesticide detection down to 20 ppb. This universal approach offers portable, cost effective fabrication of efficient SERS substrates at the point of care. This approach should bring SERS closer to the real world through ink cartridges to be fixed to a pen to create plasmonic sensors at will.     

Spherical Nanoparticle Arrays with Tunable Nanogaps and Their Hydrophobicity Enhanced Rapid SERS Detection by Localized Concentration of Droplet Evaporation

Periodic hexagonal spherical nanoparticle arrays are fabricated by a sacrificial colloidal monolayer template route by chemical deposition and further physical deposition. The regular network‐structured arrays are first templated by colloidal monolayers and then they are changed to novel periodic spherical nanoparticle arrays by further sputtering deposition due to multiple direction deposition and shadow effect between adjacent nanoparticles. The nanogaps between two adjacent spherical nanoparticles can be well tuned by controlling deposition time. Such periodic nanoparticle arrays with gold coatings demonstrate a very stable and high sensitive surface‐enhanced Raman scattering spectroscopy (SERS) performance. The periodic nanoparticle arrays with 10 nm gaps display much stronger SERS enhancement due to electromagnetic coupling. The chemically modified nanoparticle arrays show good hydrophobicity, which shorten process of detecting probe molecules using them as SERS‐active substrates by localized concentration of droplet evaporation and a low detection limit of 10⁻¹² m R6G can be achieved without solution wasting in a short time. The hydrophobic substrate offers a simple, convenient, and economical method to examine SERS performance by rapid concentration of solution on it and it is highly helpful to improve its practical applications in portable Raman detecting devices to detect organic molecules.     

Highly-ordered, 3D petal-like array for surface-enhanced Raman scattering

Despite the great potential of the application of surface-enhanced Raman scattering (SERS), the difficulty in fabricating suitable SERS substrates is still a problem. Based on the self-assembly of silica nanoparticles, a simple method is here proposed to fabricate a highly-ordered, 3D, petal-like arrayed structure (3D PLAS) that serves as a promising SERS substrate for both its high reproducibility and enormous SERS enhancement. Such a novel structure is easily achieved by anisotropically etching a self-assembly bilayer of silica nanoparticles, followed by metal deposition. The SERS performance of the 3D PLAS and its relationship with the main parameters, including the etching time, the diameter of silica nanoparticles, and the deposited metal film, are characterized using 632.8 nm incident light. With Rhodamine 6G as a probe molecule, the spatially averaged SERS enhancement factor is on the order of 5 × 10(7) and the local enhancement factor is much higher, both of which can be improved further by optimizing the parameters.     

Atomic layer deposition of platinum thin films on anodic aluminium oxide templates as surface-enhanced Raman scattering substrates

Platinum thin films are deposited on anodic aluminium oxide (AAO) templates by atomic layer deposition (ALD). The highly ordered island-like platinum nanostructures formed on the AAO template produce a high Raman scattering signal because of the periodical hexagonal arrangement. As an illustration, dramatic enhancement is achieved using Rhodamine 6G (R6G) as a molecular probe.Field-emission scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM) show that the gap between the island-like structures is below 10 nm. Owing to activation by the incident laser beam, the localized electromagnetic field on the platinum island surface can be dramatically enhanced by the sub-10 nm regime subsequently amplifying the Raman signal. Finite-difference time-domain (FDTD) calculation matches the experimental phenomena suggesting that the excellent surface-enhanced Raman scattering (SERS) characteristics of the platinum structure arise from the high density and abundance of hot spots. Because the platinum film is inert in air, the SERS enhancing substrate can be used reliably in many trace chemical and biological detection applications.