Raman Probe Molecule Research Articles

Assessment of SERS activity and enhancement factors for highly sensitive gold coated substrates probed with explosive molecules

The surface enhanced Raman spectroscopy (SERS) is one of the most sensitive tools for trace analysis and the fabrication of effective and robust SERS substrates is the subject of intensive research in view of their possible applications. In this Letter, the SERS activity of an ordered structure of inverted pyramids (Klarite, Ltd) was examined by using nitro-based explosives, as Raman probe molecules. Enhancement factors up to 106 and detection limits of tens of pg were measured with an excellent run to run reproducibility. These findings provide new opportunities for the utilization of SERS for analytical detection at trace level.

Differently Environment Stable Bio-Silver Nanoparticles: Study on Their Optical Enhancing and Antibacterial Properties

Generally, limited research is extended in studying stability and applicational properties of silver nanoparticles (Ag NPs) synthesized by adopting ‘green chemistry’ protocol. In this work, we report on the synthesis of stable Ag NPs using plant-derived materials such as leaf extract of Neem (Azadirachta indica) and biopolymer pectin from apple peel. In addition, the applicational properties of Ag NPs such as surface-enhanced Raman scattering (SERS) and antibacterial efficiencies were also investigated. As-synthesized nanoparticles (NPs) were characterized using various instrumentation techniques. Both the plant materials (leaf extract and biopolymer) favored the synthesis of well-defined NPs capped with biomaterials. The NPs were spherical in shape with an average particle size between 14-27 nm. These bio-NPs exhibited colloidal stability in most of the suspended solutions such as water, electrolyte solutions (NaCl; NaNO3), biological solution (bovine serum albumin), and in different pH solutions (pH 7; 9) for a reasonable time period of 120 hrs. Both the bio-NPs were observed to be SERS active through displaying intrinsic SERS signals of the Raman probe molecule (Nile blue A). The NPs were effective against the Escherichia coli bacterium when tested in nutrient broth and agar medium. Scanning and high-resolution transmission electron microscopy (SEM and HRTEM) images confirmed cellular membrane damage of nanoparticle treated E. coli cells. These environmental friendly template Ag NPs can be used as an antimicrobial agent and also for SERS based analytical applications.

Surface-enhanced Raman scattering of 4-aminobenzenethiol on silver nanoparticles substrate

Active surface-enhanced Raman scattering (SERS) silver nanoparticles substrate was prepared by multiple depositions of Ag nanoparticles on glass slides. The substrate is based on five depositions of Ag nanoparticles on 3-aminopropyl-trimetoxisilane (APTMS) modified glass slides, using APTMS sol–gel as linker molecules between silver layers. The SERS performance of the substrate was investigated using 4-aminobenzenethiol (4-ABT) as Raman probe molecule. The spectral analyses reveal a 4-ABT Raman signal enhancement of band intensities, which allow the detection of this compound in different solutions. The average SERS intensity decreases significantly in 4-ABT diluted solutions (from 10−4 to 10−6molL−1), but the compound may still be detected with high signal/noise ratio. The obtained results demonstrate that the Ag nanoparticles sensor has a great potential as SERS substrate.

Facile one-step synthesis of Ag@Fe3O4 core–shell nanospheres for reproducible SERS substrates

A facile approach has been developed to synthesize Ag@Fe3O4 core–shell nanospheres, in which the Ag nanoparticle core was well wrapped by a permeable Fe3O4 shell. An in situ reduction of AgNO3 and Fe(NO3)3 was the basis of this one-step method with ethylene glycol as the reducing agent. The as-obtained Ag@Fe3O4 nanospheres were a highly efficient surface-enhanced Raman scattering (SERS) substrate; high reproducibility, stability, and reusability were obtained by employing 4-aminothiophenol (4-ATP) and rhodamine 6G (R6G) as the Raman probe molecules. It was revealed that the SERS signals of 4-ATP and R6G on the Ag@Fe3O4 nanospheres were much stronger than those on the pure Ag nanoparticles, demonstrating that the magnetic enrichment procedures can improve SERS detection sensitivity efficiently. A highly efficient and recyclable SERS substrate was produced by the new model system that has potential applications in chemical and biomolecular assays.

Ag–Y2O3:Eu3+ composite nanotubes: synthesis, tunable photoluminescence and surface-enhanced Raman scattering

Ag–Y2O3:Eu3+ composite nanotubes were synthesized by growing Ag nanoparticles on the surface of Y2O3:Eu3+ nanotubes. The effects of the Ag content on the photoluminescence properties of the Ag–Y2O3:Eu3+ composite nanotubes were investigated in detail. In addition to the charge transfer from the 2p orbital of O2− to the 4f orbital of Eu3+, several sharp lines corresponding to the f–f transitions of Eu3+ were also observed in the excitation spectra of the Y2O3:Eu3+ nanotubes monitored at different emission wavelengths. However, only one excitation band centered at 535 nm was observed in the excitation spectrum of Ag–Y2O3:Eu3+ monitored at 590 nm, which is different from that monitored at 614 nm. We suggest that the change in the excitation spectra between Y2O3:Eu3+ and Ag–Y2O3:Eu3+ is attributed to the interaction between Ag and Ag–Y2O3:Eu3+. In particular, the inhomogeneous linewidth of the 5D0 → 7F1 transition from Ag–Y2O3:Eu3+ was observed to broaden when the excitation wavelength was set at 535 nm. Decay dynamics were performed to study the photoluminescence of the Ag–Y2O3:Eu3+ composite nanotubes, and the decay curve can be well fitted with a second order exponential decay function. Moreover, the surface-enhanced Raman scattering effect of the Ag aggregates was evaluated by using 4-aminothiophenol as a Raman probe molecule. It was demonstrated that a high SERS signal can be observed by increasing the Ag : Ln3+ ratios in the Ag–Y2O3:Eu3+ composite nanotubes.

Improving correlated SERS measurements with scanning electron microscopy: an assessment of the problem arising from the deposition of amorphous carbon

For surface-enhanced Raman scattering (SERS) substrates with nonspherical symmetry, it is critical to correlate spectroscopy measurements with imaging by scanning electron microscopy (SEM). However, the deposition of carbon resulting from e-beam exposure during SEM imaging contaminates the surface of nanoparticles, potentially preventing their further functionalization with Raman probe molecules. In addition, the deposited carbon leads to unwanted background SERS signals. In this study, we systematically investigated the deposition of carbon during SEM imaging and examined how it affects the functionalization of nanoparticles with probe molecules and impacts the detection of SERS signals. Significantly, we found that the carbon could be removed or replaced from the surface of Ag nanoparticles through chemical or physical means, rendering the nanoparticles the capability for correlated SEM/SERS studies.

Graphene Oxide Sheath on Ag Nanoparticle/Graphene Hybrid Films as an Antioxidative Coating and Enhancer of Surface-Enhanced Raman Scattering

Surface-enhanced Raman scattering (SERS) has been extensively investigated since its discovery on rough Ag surface because of high sensitivity and resolution. Ag nanostructures are considered highly active for SERS but their liability to oxidization impedes their practical applications as a SERS-based sensing platform. Here, we show that graphene oxide (GO) coating on the polyallylamine hydrochloride (PAA) functionalized Ag nanoparticles (PAA-AgNP) immobilized on PAA-functionalized reduced GO (PAA-RGO) films (GO/PAA-AgNP/PAA-RGO, sandwich structure) protect AgNPs from oxidation under ambient condition for prolonged time up to 72 days with increased and reproducible SERS signals and fast adsorption kinetics of rhodamine 6G, a model Raman probe molecule. The present strategy for GO coating on top of the immobilized AgNPs will be useful for the development of an efficient SERS-based chemical and biosensor because of its simplicity, cost-effectiveness, long-term stability, and high reproducibility.

Novel Molecular Specific Detection of Glucose Using a Raman Probe Molecule with Surface Enhanced Raman Scattering

We report on two new and improved glucose detection techniques based on surface enhanced Raman scattering (SERS) spectroscopy that are molecular specific to glucose and sensitive in the physiological concentration range (0.9 to 30 mM). Two novel methods were designed and evaluated to enhance the SERS signal of a Raman probe molecule towards glucose detection. The first method utilizes solid gold nanoparticle-coated zinc oxide nanowires (AuNP–ZnONWs) as a SERS substrate together with a Raman probe molecule, 3,3 � boronic benzyl viologen (BBV), designed to bind specifically to glucose for its detection via SERS of BBV. The second method, utilizing silver nanoparticles (AgNPs) as a SERS substrate with BBV, enables glucose detection down to a concentration of 0.25 mM with high reproducibility, specificity, and sensitivity. The fundamental mechanism behind each of these approaches is analyzed and discussed. Electrostatic interaction between the substrate and BBV is found to be most critical in determining SERS activity. This work holds potential for development of a molecular specific, sensitive, and noninvasive glucose detection method for monitoring diabetes.

Highly Sensitive and Transparent Surface Enhanced Raman Scattering Substrates Made by Active Coldly Condensed Ag Nanorod Arrays

We report a simple and robust method to fabricate highly sensitive and transparent silver nanorod (AgNR) array substrates for surface enhanced Raman scattering (SERS) using low temperature oblique angle deposition technique. These highly sensitive AgNR SERS substrates consist of tilted AgNRs deposited on glass slides at a substrate temperature T = 140 K. The results show that the substrate temperature plays a crucial role in determining both the morphology and the length of AgNRs. The SERS enhancement activity of these substrates was determined using trans-1,2-bis(4-pyridyl) ethylene as a Raman probe molecule. The highest SERS response was obtained from 1 μm long AgNRs fabricated at T = 140 K. Such a deposition reduces the deposition time to 1/4 when compared to similar length AgNRs deposited at room temperature. The effect of the manifestly different surface morphology of low temperature deposited AgNRs on the SERS enhancement is demonstrated by finite-difference time-domain calculations of local field enhancements. The AgNRs arrays grown at 140 K exhibit uniform SERS response and good optical transmission and are cost-effective, which makes this fabrication method a practical choice as a next generation alternative for SERS substrate fabrication.

Multifunctional ZnO/Ag nanorod array as highly sensitive substrate for surface enhanced Raman detection

A multifunctional ZnO/Ag nanorod arrays has been prepared to construct SERS-active and photocatalytic substrate by a hydrothermal method. The morphology, microstructure and optical properties of ZnO/Ag nanorod arrays are characterized by X-ray diffraction spectra, field emission scanning electron microscopy, energy-dispersive, ultraviolet–visible (UV–vis) absorption and photoluminescence measurement to confirm the successful Ag deposition on the ZnO nanorod arrays. Such arrays exhibit strong and reproducible SERS signals of the Raman probe molecules. The mechanism of SERS enhancement was discussed due to the formation of interfacial electric field between ZnO nanorods and Ag. Furthermore, ZnO/Ag nanorod arrays also show catalytic properties by photocatalytic degradation of target molecules adsorbed to the substrate, which provides promising application for detecting and eliminating organic pollutant.

Surface-Enhanced Raman Spectroscopy of Carbon Nanotubes in Aqueous Solution

Carbon nanotubes (CNTs) exhibit intrinsic spectroscopic properties and are potential Raman and NIR florescence probes for bioimaging. However, the weak Raman intensity greatly obstructs such applications. Surface-enhanced Raman scattering (SERS) has shown to be an effective way to increase the Raman signal. SERS has been widely studied for solid samples. However, solid state is distinctly different from the environment in biosystems. Herein, we studied the SERS of Au- nanoparticle-decorated CNTs in aqueous solution, which offers a similar environment to biosystems. We found that the func- tionalization of CNTs with -SH groups can improve the attachment of Au nanoparticles on tube surfaces thus benefit the SERS effect. The particle size is another important issue for SERS. Particles of 50 nm show much stronger enhancement than those of 12 nm. The Raman intensity of CNTs increases with the increase of the concentration of Au nanoparticles. Hexame- thylene diamine molecules can act as the bi-linkers between Au nanoparticles, compressing the interparticle distance. This was proved by the red-shift of the band at ca. 540 nm and the appearance of a broad band around 700 nm in the absorption spectra of Au nanoparticles. Therefore the addition of hexamethylene diamine can further increase the Raman signal of CNTs by the strong coupling of the surface plasma from the Au nanoparticles with very small interparticle distances. Two kinds of commonly used small molecule Raman probes p-aminothiophenol and Rhodamine B both show remarkably enhanced Raman intensity when added to the aqueous dispersion of Au/CNT hybrids. This shows that these Raman probe molecules can ab- sorb onto the Au/CNT hybrids and their Raman spectra are able to be greatly enhanced by Au nanoparticles decorated on CNTs. Because various Raman bands from either CNTs or Raman probe molecules can be used for Raman imaging, this kind of Raman probe molecule/Au/CNT tri-component hybrid systems may be used as a potential nanostructured platform for multiplexed Raman imaging based on SERS effect. Keywords carbon nanotubes; gold nanoparticles; surface enhanced Raman scattering (SERS); Raman spectroscopy for aqueous solution

Flexible and mechanical strain resistant large area SERS active substrates

We report a cost effective and facile way to synthesize flexible, uniform, and large area surface enhanced Raman scattering (SERS) substrates using an oblique angle deposition (OAD) technique. The flexible SERS substrates consist of 1 μm long, tilted silver nanocolumnar films deposited on flexible polydimethylsiloxane (PDMS) and polyethylene terephthalate (PET) sheets using OAD. The SERS enhancement activity of these flexible substrates was determined using 10(-5) M trans-1,2-bis(4-pyridyl) ethylene (BPE) Raman probe molecules. The in situ SERS measurements on these flexible substrates under mechanical (tensile/bending) strain conditions were performed. Our results show that flexible SERS substrates can withstand a tensile strain (ε) value as high as 30% without losing SERS performance, whereas the similar bending strain decreases the SERS performance by about 13%. A cyclic tensile loading test on flexible PDMS SERS substrates at a pre-specified tensile strain (ε) value of 10% shows that the SERS intensity remains almost constant for more than 100 cycles. These disposable and flexible SERS substrates can be integrated with biological substances and offer a novel and practical method to facilitate biosensing applications.

One‐pot synthesis of silver particle aggregation as highly active SERS substrate

AbstractSilver particles with different degrees of aggregation were synthesized through a sodium dodecyl sulfate‐assisted one‐pot reaction in an aqueous medium. The products were characterized by transmission electron microscopy, scanning electron microscopy and UV‐visible spectroscopy. The results showed that the degree of aggregation of the Ag nanoparticles could be tuned by changing the reaction parameters, such as the reaction temperature and time. A possible formation process of the Ag aggregate is proposed on the basis of a series of experimental results. Moreover, the surface‐enhanced Raman scattering (SERS) effect of the Ag aggregates was evaluated by using rhodamine 6G as a Raman probe molecule. It was demonstrated that the SERS enhancement ability is related to the degree of aggregation of Ag particles, and a high SERS signal can be observed by selecting Ag nanoparticles with the proper degree of aggregation as substrates. Moreover, the aggregates showed good reproducibility and stability to SERS from organic molecules. Copyright © 2010 John Wiley & Sons, Ltd.

Silver-embedded zeolite crystals as substrates for surface-enhanced Raman scattering

This paper reports the preparation of a type of Ag-embedded zeolite crystals as surface-enhanced Raman spectroscopy (SERS) substrates by chemical reduction of Ag+-exchanged ZSM-5. Ag+ ions were loaded into the zeolite framework by ion exchange. Then the exchanged-Ag+ ions were reduced and metallic silver clusters formed inside the zeolite channel. The resulting Ag-embedded zeolite crystals are characterized by using a number of techniques including X-ray diffraction, scanning electron microscopy, and X-ray photoelectron spectroscopy to confirm silver formed inside the crystal channel. The fabricated Ag-embedded ZSM-5 zeolite substrates displayed strong and reproducible SERS activity for different Raman probe molecules such as Tris(2,2′-bipyridyl) ruthenium(II) chloride (RuBpy) and rhodamine 6G (R6G). Since silver embedded into the zeolite channel without changing the crystal surface property, the Ag–ZSM-5 zeolite crystal can be used to prepare different SERS-active substrate (SERS-tags), in which different probe molecules may be detected. Such Ag-embedded zeolite substrate would be useful in chemical and biological sensing and in the development of SERS-based analytical devices.

A durable plastic substrate for surface-enhanced Raman spectroscopy

A novel durable substrate has been prepared for surface-enhanced Raman spectroscopy (SERS). The substrate is fabricated by reduction of silver nitrate using poly(vinyl pyrrolidone) (PVP) polymer as stabilizers. The SERS-active particles are based on poly(methylmethacrylate) (PMMA) materials, producing stable and optically translucent substrates. The stability of silver particles on the substrate was demonstrated by characterizing the localized surface plasmon resonance (LSPR) band of the elemental silver particles. The SERS activity was evaluated by detecting the signal from Raman probe molecules, Rhodamine 6G (R6G). This plastic substrate material is easy to prepare, inexpensive, and sturdy for SERS applications.

Preparation and Molecular Recognition of SERS Probe Based on Gold Nanoparticles Constructed from PEG–Oligoamine Copolymer Possessing a Coumarin Group between PEG and Oligoamine

Abstract Novel gold nanoparticles (GNPs) as a SERS probe were prepared using two types of functional PEG/oligoamine polymers possessing biotin as biotag molecules at the PEG end or a coumarin moiety as a Raman probe molecule between the PEG and oligoamine segments. Eventually, the GNPs showed excellent dispersion stability under physiological conditions, as well as remarkable SERS signal resulting from molecular recognition between streptavidin and the biotin tag, even in the presence of bovine serum albumin (BSA).

A General Strategy to Prepare TiO(2)-core Gold-shell Nanoparticles as SERS-tags.

The synthesis and characterization of TiO(2)-based core-shell nanoparticles as surface-enhanced Raman Scattering (SERS) tags are reported. A hydrolysis approach is first used to generate colloidal TiO(2) nanoparticles, which are subsequently tagged with Raman probe molecules and encapsulated within a gold nanoshell. The resulting core-shell nanoparticles are characterized by using a number of techniques including UV-visible spectroscopy, transmission electron microscopy, and energy-dispersive X-ray spectroscopy (EDX) to confirm the successful coating of the Au shells. These core-shell nanoparticles exhibit very strong and reproducible SERS signals of the Raman probe molecules. Three different types of Raman probe molecules are used to prepare different SERS-active nanoparticles (SERS-tags), which demonstrates the versatility of the design. Such TiO(2)-based metal-coated core-shell nanoparticles will be useful as SERS-tags in biological assay and imaging applications. They may also provide a platform for fundamental studies in the ongoing investigations on the mechanisms of SERS.

Surface Enhanced Raman Scattering from an Ag Nanorod Array Substrate: The Site Dependent Enhancement and Layer Absorbance Effect

We have designed experiments to put Raman probe molecules on different locations of Ag nanorod array substrates and found that the apparent enhancement factor for surface enhanced Raman scattering (SERS) is about 50−200 times from the surface of the nanorods than that from the Ag thin film surface under an Ag nanorods array. When excited from the top of Ag nanorod array substrates, the ratio of SERS intensity excited by s-polarization to that excited by p-polarization is 1.8 to 2.2, while when excited from the bottom of Ag nanorod array substrates, this ratio becomes 0.77. These effects cannot be interpreted directly by the local electric field enhancement effect. By combining the local electric field effect calculated by the three-dimensional finite-difference time-domain method and the anisotropic optical absorbance of the SERS signal from the anisotropic Ag nanorod array, the numerical calculations semiquantitatively agree with the experimental results.

Polarization-Dependent Surface Enhanced Raman Scattering from Silver 1D Nanoparticle Arrays

Arrays of linear, one-dimensional (1D) silver nanoparticle rows have been synthesized that demonstrate strong surface enhanced Raman scattering (SERS) that is dependent on the polarization of the incident electromagnetic radiation. Ordered arrays of 1D rows of spherical silver nanoparticles were fabricated on highly oriented pyrolytic graphite (HOPG) by physical vapor deposition (PVD) at 400 °C. Scanning electron microscopy confirmed the formation of arrays of highly parallel rows of nanoparticles. The rows are typically hundreds of microns long with particle gaps less than 10 nm and 10−1000 nm spacing between adjacent 1D rows. The polarization dependence of the SERS was characterized using thiophenol as a Raman probe molecule that was adsorbed as a monolayer on the silver nanoparticle surfaces. When incident light is polarized along the axis of the nanoparticle rows, the intensity of the Raman-scattered light was ≈20 times stronger than Raman scattered light when the incident radiation was polarized perp...