Search

Despite the excellent surface-enhanced Raman scattering (SERS) activity, the poor chemical stability of Ag nanoparticles severely hinders their application as SERS substrates. In this paper, a two-step process was used to prepare highly sensitive and chemically stable Ag@Au hetero-architectures, in situ growth of Ag nanoparticles on a Si wafer followed by Au coating through ion sputtering. Owing to the chemical inertness of Au, the Ag@Au hetero-architecture substrates exhibited enhanced chemical stability compared to pure Ag nanoparticle substrates. In particular, the deposition of Au coatings could efficiently modulate the gap between the neighboring Ag nanoparticles and strengthen the surface plasmon coupling effect. As a consequence, the Ag@Au hetero-architecture substrates exhibited a higher SERS sensitivity than pure Ag nanoparticle substrates. Furthermore, a possible mechanism for the enhanced SERS sensitivity of the Ag@Au hetero-architecture substrates was proposed and discussed. The present work came up with an effective and facile way to tune SERS sensitivity and chemical stability of Ag nanoparticle substrate, and in the meantime, implied a promising SERS application in oxidative environments or biological systems. This journal is

Mitochondrial pH (pHmito) is intimately related to mitochondrial function, and aberrant values for pHmito are linked to several disease states. We report the design, synthesis, and application of mitokyne 1-the first small molecule pHmito sensor for stimulated Raman scattering (SRS) microscopy. This ratiometric probe can determine subtle changes in pHmito in response to external stimuli and the inhibition of both the electron transport chain and ATP synthase with small molecule inhibitors. In addition, 1 was also used to monitor mitochondrial dynamics in a time-resolved manner with subcellular spatial resolution during mitophagy providing a powerful tool for dissecting the molecular and cell biology of this critical organelle.

Surface enhanced Raman scattering (SERS) is a technique that demonstrates a number of advantages for the rapid, specific and sensitive detection of pathogenic microorganisms. In this review, an overview of label-free and label-based SERS approaches, including microfluidics, nucleic acid detection and immunoassays, for the multiplexed detection of pathogenic bacteria and viruses from the last decade will be discussed, as well as their transition into promising point-of-use detection technologies in industrial and medical settings., In this review we discuss surface enhanced Raman scattering (SERS) based techniques for the multiplexed detection of pathogenic microorganisms and their transition into point-of-use detection technologies in the field.

Plasmonic Ag nano-assemblies moving in a living cell were employed to visualize the spatiotemporal change of intracellular pH by surface-enhanced Raman scattering. Ag nano-assemblies were functionalized with 4-mercaptobenzoic acid (p-MBA) to monitor the variation of the surrounding pH. SERS spectra from the functionalized nano-assemblies that were transported in a cell were recorded to estimate the local pH on the pathways travelled by the nano-assemblies. 3D nanoparticle tracking and SERS measurements were simultaneously performed to trace the pH dynamics with a spatial accuracy of several tens of nanometers and a temporal resolution of 200 ms, which are sufficient to reveal pH changes associated with intracellular transportation. The pH trajectory of the functionalized nanoparticle can be used to visualize the dynamic change of the chemical environment caused by organelle interactions, such as endosomal trafficking and lysosomal fusion. This breakthrough creates a new paradigm for intracellular analysis using SERS and reveals new capability for rapid use of SERS in biological analysis.

Raman and near-infrared (NIR) chemical mapping are widely used methods in the pharmaceutical industry to understand the distribution of components within a drug product. Recent advancements in instrumentation have enabled the rapid acquisition of high-resolution images. The comparison of these techniques for the analysis of pharmaceutical tablets has not recently been explored and thus the relative performance of each technique is not currently well defined. Here, the differences in the chemical images obtained by each method are assessed and compared with scanning electron microscopy with energy dispersive X-ray microanalysis (SEM-EDX), as an alternative surface imaging technique to understand the ability of each technique to acquire a chemical image representative of the sample surface. It was found that the Raman data showed the best agreement with the spatial distribution of components observed in the SEM-EDX images. Quantitative and qualitative comparison of the Raman and NIR images revealed a very different spatial distribution of components with regards to domain size and shape. The Raman image exhibited sharper and better discriminated domains of each component, whereas the NIR image was heavily dominated by large pixelated domains. This study demonstrated the superiority of using Raman chemical mapping compared with NIR chemical mapping to produce a chemical image representative of the sample surface using routinely available instrumentation to obtain a better approximation of domain size and shape. This is fundamental for understanding knowledge gaps in current manufacturing processes; particularly relating the relationship between components in the formulation, processing condition, and final characteristics. By providing a means to more accurately visualize the components within a tablet matrix, these areas can all be further understood.

In order to improve patient survival and reduce the amount of unnecessary and traumatic biopsies, non-invasive detection of cancerous tumours is of imperative and urgent need. Multicellular tumour spheroids (MTS) can be used as an ex vivo cancer tumour model, to model in vivo nanoparticle (NP) uptake by the enhanced permeability and retention (EPR) effect. Surface enhanced spatially offset Raman spectroscopy (SESORS) combines both surface enhanced Raman spectroscopy (SERS) and spatially offset Raman spectroscopy (SORS) to yield enhanced Raman signals at much greater sub-surface levels. By utilizing a reporter that has an electronic transition in resonance with the laser frequency, surface enhanced resonance Raman scattering (SERRS) yields even greater enhancement in Raman signal. Using a handheld SORS spectrometer with back scattering optics, we demonstrate the detection of live breast cancer 3D multicellular tumour spheroids (MTS) containing SERRS active NPs through 15 mm of porcine tissue. False color 2D heat intensity maps were used to determine tumour model location. In addition, we demonstrate the tracking of SERRS-active NPs through porcine tissue to depths of up to 25 mm. This unprecedented performance is due to the use of red-shifted chalcogenpyrylium-based Raman reporters to demonstrate the novel technique of surface enhanced spatially offset resonance Raman spectroscopy (SESORRS) for the first time. Our results demonstrate a significant step forward in the ability to detect vibrational fingerprints from a tumour model at depth through tissue. Such an approach offers significant promise for the translation of NPs into clinical applications for non-invasive disease diagnostics based on this new chemical principle of measurement.

The development of viable point-of-care diagnostic formats is integral to achieving better patient care and improved outcomes. The need for robust and low-cost tests is especially important in under-resourced and rural settings. Perhaps the greatest challenge is ensuring that an untrained individual is capable of operating and interpreting the test, out with a care facility. Here we present a paper-based diagnostic device capable of sensing miR-29a using both colorimetric and surface enhanced Raman scattering (SERS) analysis. Rather, than carry out the two types of analyses in tandem, we envisage that the colorimetric output is easy enough to be interpreted by the untrained-individual administering the test to provide them with qualitative feedback. If deemed positive, the test can be further validated at a centralized care facility using a handheld-Raman spectrometer to provide a semi-quantitative result. Detection of miR-29a, a microRNA associated with myocardial infarction, was achieved at a level of pg μL-1 through the combination of three-dimensional paper-based microfluidics, colorimetric detection, and surface enhanced Raman scattering (SERS) analysis. RGB analysis of the colorimetric output generated from samples containing miR-29a at different concentrations (18-360 pg μL-1) showed differentiation from the control sample, however significant repeat variability indicated that it could not be used for quantifying miR-29a levels. However, the SERS analysis exhibited greater reproducibility at varying concentrations, achieving an LoD of 47 pg μL-1. The union of the paper-based device and the two analysis methods resulted in the production of a sensitive, reproducible and facile, point of care test (POCT), which paves the way for future implementation in the diagnosis of a range of diseases.

The discovery of the enhancement of Raman scattering by molecules adsorbed on nanostructured metal surfaces is a landmark in the history of spectroscopic and analytical techniques. Significant experimental and theoretical effort has been directed toward understanding the surface-enhanced Raman scattering (SERS) effect and demonstrating its potential in various types of ultrasensitive sensing applications in a wide variety of fields. In the 45 years since its discovery, SERS has blossomed into a rich area of research and technology, but additional efforts are still needed before it can be routinely used analytically and in commercial products. In this Review, prominent authors from around the world joined together to summarize the state of the art in understanding and using SERS and to predict what can be expected in the near future in terms of research, applications, and technological development. This Review is dedicated to SERS pioneer and our coauthor, the late Prof. Richard Van Duyne, whom we lost during the preparation of this article., Funding is acknowledged from the European Research Council (ERC Advanced Grant No. 787510-4DBIOSERS to L.M.L.-M., ERC Advanced Grant No. 789104-eNANO to F.J.G.A., ERC Starting Grant No. 259432-MULTIBIOPHOT to J.K., ERC Consolidator Grant No. 772108-DarkSERS); the Department of Education of the Basque Government (Grant No. IT1164-19 to J.A.); the Spanish MINECO (CTQ2017-88648-R to R.A.-P., MAT2016-77809-R to I.P.-S. and J.P.-J.); the EPSRC (EP/P034063/1 to S.B., EP/L027151/1 to J.B., EP/L014165/1 to D.G. and K.F.); IDUN-Danish National Research Foundation (DNRF122) and Villum Fonden (Grant No. 9301) to A.B.; the National Research Foundation of Korea (Grant No. 2019R1A2C3004375 to J.B.); the German Science Foundation, DFG (SFB 1278 Polytarget (Project B4) to V.D., Grant No. SCHL 594/13-1 to S.S., Germany’s Excellence Strategy (EXC 2089/1-390776260) to S.M.); the Federal Ministry of Education and Research, Germany (BMBF) (Grant InfectoGnostics 13GW0096F to D.C.-M. and J.P.); DARPA-16-35-INTERCEPT-FP-018 to L.F.; the UK BBSRC (Grant No. BB/L014823/1 to R.G.); the Department of Science and Technology (DST Nanomission Project SR/NM/NS-23/2016 to K.G.T.); the U.S. National Science Foundation (Grant No. CHE-1707859 to A.J.H., Center for Sustainable Nanotechnology CHE-1503408 (Centers for Chemical Innovation Program) to C.L.H., Center for Chemical Innovation Chemistry at the Space-Time Limit (CaSTL) CHE-1414466 to G.C.S. and R.P.V.D., Grant No. CHE-1807269 to K.A.W.); the Knut and Alice Wallenberg Foundation to M.K.; the Office of Naval Research (Grant No. N00014-18-1-2876 to N.A.K.); Royal Society of New Zealand Te Apa̅rangi to E.L.R. and B.A.; Singapore Ministry of Education, Tier 1 (RG11/18) to X.Y.L.; the Photoexcitonix Project in Hokkaido Univ., Japan, to K.M.; BioNano Health-Guard Research Center funded by the Ministry of Science and ICT (MSIT) of Korea as Global Frontier Project (Grant No. H-GUARD_2013M3A6B2078947) to J.-M.N.; NSFC of P. R. China (Grant No. 21705015 to Y.O., Grant No. 21633005 to B.R.); National Key R&D Program (2017YFA0206902) to C.X. This work was coordinated under the Maria de Maeztu Units of Excellence Program from the Spanish State Research Agency—Grant No. MDM-2017-0720.

The photothermal release of single stranded DNA (ssDNA) from the surface of gold nanoparticles of different shapes and sizes is a promising mode of delivering DNA for gene-therapy applications. Here, we demonstrate the first targeted photothermal release of ssDNA from hollow gold nanospheres (HGNs) and analyse the release of the ssDNA using quantitative surface enhanced Raman scattering (SERS). The HGNs used demonstrate a tunable localized surface plasmon resonance (LSPR) frequency while maintaining size consistency, allowing for selective ssDNA release based on matching the excitation frequency to the plasmon resonance. It is shown that HGNs with resonances at 760 and HGN 670 nm release significant amounts of ssDNA when excited via 785 nm and 640 nm lasers respectively. When excited with a wavelength far from the LSPR of the particles, the ssDNA release is negligible. This is the first demonstration of SERS to analyze the amount of ssDNA photothermally released from the surface of HGNs. In contrast to traditional fluorescence measurements, this SERS based approach provides quantitatively robust data for analysis of ssDNA release and lays a strong foundation for future studies exploiting plasmonically induced ssDNA release.

Duncan Graham opened a general discussion of the paper by Pavel Matousek: Regarding the temperature measurements, how did you do them? Stokes/anti-Stokes measurement? The values are not what I'd expect and seem lower. What was the wavelength and power of the laser and did you calculate what you thought the temperature measurement should be based on that? How far does the temperature gradient reach? The scattering absorption ration changes with nanoparticle size and composition. Have you thought about using more highly absorbing nanoparticles such as hollow gold nanoshells?

Infrared surface enhanced Raman scattering (SERS) is an attractive technique for the in situ detection of nanoprobes in biological samples due to the greater depth of penetration and reduced interference compared to SERS in the visible region. A key challenge is to understand the surface layer formed in suspension when a specific label is added to the SERS substrate in aqueous suspension. SERS taken at different wavelengths, theoretical calculations, and surface-selective sum frequency generation vibrational spectroscopy (SFG-VS) were used to define the surface orientation and manner of attachment of a new class of infrared SERS label with a thiopyrylium core and four pendant 2-selenophenyl rings. Hollow gold nanospheres (HGNs) were used as the enhancing substrate and two distinct types of SERS spectra were obtained. With excitation close to resonance with both the near infrared electronic transition in the label (max 826 nm) and the plasmon resonance maximum (690 nm), surface enhanced resonance Raman scattering (SERRS) was obtained. SERRS indicates that the major axis of the core is near to perpendicular to the surface plane and SFG-VS obtained from a dried gold film gave a similar orientation with the major axis at an angle 64°-85° from the surface plane. Longer excitation wavelengths give SERS with little or no molecular resonance contribution and new vibrations appeared with significant displacements between the thiopyrylium core and the pendant selenophene rings. Analysis using calculated spectra with one or two rings rotated indicates that two rings on one end are rotated towards the metal surface to give an arrangement of two selenium and one sulphur atoms directly facing the gold structure. The spectra, together with a space filled model, indicate that the molecule is strongly adsorbed to the surface through the selenium and sulphur atoms in an arrangement which will facilitate layer formation.

Resonant chalcogenpyrylium nanotags demonstrate an exceptional surface enhanced Raman scattering (SERS) performance for use in SORS applications. Using surface enhanced spatially offset Raman spectroscopy (SESORS), nanotags modified with a chalcogenpyrylium dye were observed at concentrations as low as 1 pM through 5 mm of tissue. Calculated limits of detection suggest that these SERS nanotags can be detected at 104 fM using surface enhanced spatially offset resonance Raman scattering (SESORRS) demonstrating their potential for in vivo applications.

Surface enhanced Raman scattering (SERS) can provide high sensitivity detection of an analyte, specific identification of the analyte in situ in a matrix and identification of several analytes in a solution without separation. The technique uses standard Raman spectrometers. It requires that the analyte is adsorbed on or close to a suitable roughened surface usually of silver or gold. Labeled nanoparticles and designed substrates have both been used successfully. Analysis using SERS detection requires that the experiment is correctly designed and this article outlines the basic theory and the practical requirements for successful analytical procedures to be developed.

To accurately predict atherosclerotic plaque progression, a detailed phenotype of the lesion at the molecular level is required. Here, we assess the respective merits and limitations of molecular imaging tools. Clinical imaging includes contrast-enhanced ultrasound (CEUS), an inexpensive and non-toxic technique but with poor sensitivity. Computed tomography (CT) benefits from high spatial resolution but poor sensitivity coupled with an increasing radiation burden that limits multiplexing. Despite high sensitivity, positron emission tomography (PET) and single-photon emission tomography (SPECT) have disadvantages when applied to multiplex molecular imaging due to poor spatial resolution, signal cross talk and increasing radiation dose. In contrast, magnetic resonance imaging (MRI) is non-toxic, displays good spatial resolution but poor sensitivity. Pre-clinical techniques include near-infrared fluorescence (NIRF), which provides good spatial resolution and sensitivity; however, multiplexing with NIRF is limited, due to photobleaching and spectral overlap. Fourier transform infrared spectroscopy (FT-IR) and Raman spectroscopy are label-free techniques that detect molecules based on the vibrations of chemical bonds. Both techniques offer fast acquisition times with Raman showing superior spatial resolution. Raman signals are inherently weak; however, leading to the development of surface-enhanced Raman spectroscopy (SERS) that offers greatly increased sensitivity due to utilising metallic nanoparticles that can be functionalised with biomolecules targeted against plaque ligands while offering high multiplexing potential. This asset combined with high spatial resolution makes SERS an exciting prospect as a diagnostic tool. The ongoing refinements of SERS technologies such as deep tissue imaging and portable systems making SERS a realistic prospect for translation to the clinic.

Surface enhanced Raman scattering (SERS) tags are in situ probes that can provide sensitive and selective probes for optical analysis in biological materials. Engineering tags for use in the near infrared (NIR) region is of particular interest since there is an uncongested spectral window for optical analysis due to the low background absorption and scattering from many molecules. An improved synthesis has resulted in the formation of hollow gold nanoshells (HGNs) with a localised surface plasmon resonance (LSPR) between 800 and 900 nm which provide effective SERS when excited at 1064 nm. Seven Raman reporters containing aromatic amine or thiol attachment groups were investigated. All were effective but 1,2-bis(4-pyridyl)ethylene (BPE) and 4,4-azopyridine (AZPY) provided the largest enhancement. At approximately monolayer coverage, these two reporters appear to pack with the main axis of the molecule perpendicular or nearly perpendicular to the surface giving strong SERS and thus providing effective 1064 nm gold SERS nanotags.

Surface enhanced Raman scattering (SERS) can generate characteristic spectral "fingerprints" from metal complexes, thus providing the potential for the development of methods of analysis for the identification and quantitation of a range of metal ions in solution. The advantages include sensitivity and the use of one ligand for several metals without the need for a specific chromophore. Aqueous solutions of Fe(II), Ni(II), Zn(II), Cu(II), Cr(III) and Cd(II) in the presence of excess 2,2'-bipyridyl (bipy) were analysed using SERS. Specific marker bands enabled the identification of each metal ion and the limit of detection for each metal ion was estimated. Two of the ions, Zn(II) and Cu(II), could be detected below the World Health Organisation's (WHO) recommended limits for drinking water at levels of 0.22 and 0.6 mg L(-1), respectively.

Surface-enhanced Raman scattering (SERS) is of interest for biomedical analysis and imaging because of its sensitivity, specificity and multiplexing capabilities. The successful application of SERS for in vivo biosensing requires probes to be biocompatible and procedures to be minimally invasive, challenges that have respectively been met by developing new nanoprobes and instrumentation. This Review presents recent developments in these areas, describing case studies in which sensors have been implemented, as well as outlining shortcomings that must be addressed before SERS sees clinical use. Surface-enhanced Raman scattering (SERS) is a physical phenomenon first discovered in 1974. SERS has since been exploited for bioanalysis because of its high sensitivity and multiplexing capabilities. This Review describes the progress made and problems faced with respect to using in vivo SERS in humans.

This is the first report of the use of a hand-held 1064 nm Raman spectrometer combined with red-shifted surface-enhanced Raman scattering (SERS) nanotags to provide an unprecedented performance in the short-wave infrared (SWIR) region. A library consisting of 17 chalcogenopyrylium nanotags produce extraordinary SERS responses with femtomolar detection limits being obtained using the portable instrument. This is well beyond previous SERS detection limits at this far red-shifted wavelength and opens up new options for SERS sensors in the SWIR region of the electromagnetic spectrum (between 950 and 1700 nm).

Since its discovery in 1974, surface-enhanced Raman scattering (SERS) has gained momentum as an important tool in analytical chemistry. SERS is used widely for analysis of biological samples, ranging from in vitro cell culture models, to ex vivo tissue and blood samples, and direct in vivo application. New insights have been gained into biochemistry, with an emphasis on biomolecule detection, from small molecules such as glucose and amino acids to larger biomolecules such as DNA, proteins, and lipids. These measurements have increased our understanding of biological systems, and significantly, they have improved diagnostic capabilities. SERS probes display unique advantages in their detection sensitivity and multiplexing capability. We highlight key considerations that are required when performing bioanalytical SERS measurements, including sample preparation, probe selection, instrumental configuration, and data analysis. Some of the key bioanalytical measurements enabled by SERS probes with application to in vitro, ex vivo, and in vivo biological environments are discussed.

Jurgen Popp opened a general discussion of the paper by Roy Goodacre: What is the advantage of using SERS instead of ordinary Raman spectroscopy?

Surface enhanced Raman scattering (SERS) is a sensitive and selective spectroscopic technique for the detection and characterization of analytes, which are adsorbed on suitable metal surfaces. The effect was first discovered experimentally in 1974 by Fleischmann et al., who reported very intense Raman bands from pyridine adsorbed onto an electrochemically roughened silver surface. They attributed this strong signal to the presence of a large number of pyridine molecules present at the roughened electrode surface due to its large surface area. However, in 1977 Jeanmaire and Van Duyne, and Albrecht and Creighton, independently recognized that the increase in intensity could not be accounted for simply by the number of scatterers present. They observed that compared with Raman scattering from the equivalent concentration of pyridine in solution, SERS gives an enhancement of ∼ 106 and concluded that an intrinsic surface enhancement effect played a fundamental role in producing the enhanced Raman scattering. In the basic process of SERS, the analyte is adsorbed onto a roughened metal surface of a suitable metal, usually silver or gold. On excitation of this surface with a laser beam, a change in polarizability of the analyte occurs in a direction perpendicular to the surface, leading to the enhanced scattering. The rough surface required for scattering can be provided in many ways. Common methods use aggregated colloidal particles, roughened electrodes, or thin cold-deposited metal films. However there are now many specially designed surfaces some of which are available commercially. With a technique which was discovered experimentally and which involves both the physics and chemistry of the interaction of light with a roughened surface and of the adsorption an analyte on a metal surface in water, air or vacuum at the molecular level it was perhaps inevitable that in the early stages of development the theory would be hotly disputed. However the process is now much better understood and it is possible to use the advantages of SERS to develop very sensitive and informative detection methods.

Discussions.

Ultrasensitive direct SERS analysis offers a powerful analytical tool for the structural characterization and classification of nucleic acids. However, acquisition of reliable spectral fingerprints of such complex biomolecules poses important challenges. In recent years, many efforts have been devoted to overcome these limitations, mainly implementing silver colloids as plasmonic substrates. However, a reliable cross-comparison of results reported in the recent literature is extremely hard to achieve, mostly due to the broad set of different surface properties of the plasmonic nanoparticles. Herein, we perform a thorough investigation of the role played by the metal/liquid interface composition of silver colloids in the direct label-free SERS analysis of DNA. Target molecules of increasing complexity, from short homopolymeric strands to long genomic duplexes, were used as probes. We demonstrate how apparently subtle changes in the colloidal surface chemistry can dramatically modify the affinity and the final SERS spectral profile of DNA. This has significant implications for the future design of new analytical strategies for the detection of DNA using SERS without labels.

This collection of surface-enhanced Raman scattering (SERS) papers has been put together to reflect the importance of the technique in modern analytical chemical research. A number of papers featuring SERS over the years have gone into understanding the phenomena and even now there are still debates about the exact mechanism of the surface enhancement depending on the nature of the system being investigated.

Surfaced enhanced Raman scattering (SERS) can discriminate between metal complexes due to the characteristic “spectral fingerprints” obtained. As a result, SERS has the potential to develop relatively simple and sensitive methods of detecting and quantifying a range of metal ions in solution. This could be beneficial for the environmental monitoring of potentially toxic metals (PTMs). Here, salen (C16H16N2O2) was used as a ligand to form complexes of Ni(II), Cu(II), Mn(II) and Co(II) in solution. The SERS spectra showed characteristic spectral differences specific to each metal complex, thus allowing the identification of each of these metal ions. This method allows a number of metal ions to be detected using the same ligand and an identical preparation procedure. The limit of detection (LOD) was determined for each metal ion, and it was found that Ni(II), Cu(II) and Mn(II) could be detected below the WHO’s recommended limits in drinking water at 1, 2 and 2 µg L-1, respectively. Co(II) was found to have an LOD of 20 µg L-1, however no limit has been set for this ion by the WHO as the concentration of Co(II) in drinking water is generally

The same interactions that a pathogen uses for establishment in a host can be exploited in its detection. The carbohydrates comprising the intestinal cell surface GM1-ganglioside, are targeted by vibrio cholerae via the lectin, cholera toxin, to initiate infection. We report on the preparation of mixed-monolayer, carbohydrate-coated silver nanoparticles (glyconanoparticles) for the sensitive (56 ng/mL), low volume detection of cholera toxin B-subunit (CTB) in synthetic freshwater samples and in 5 minutes by surface enhanced Raman spectroscopy (SERS). The detection limit falls within the recommended detection range and matches WHO approved test limits. PEGylated galactose and sialic acid are added in a specific ratio to coat the particles in GM1-ganglioside mimics for interaction with CTB and display a synergic effect greater than either glycan alone. This demonstrates the first use of a mixed-monolayer glyconanoparticle which mimics the GM1 ligand, allowing selective interaction with CTB.

Richard Dluhy opened a general discussion of the paper by Duncan Graham: In your example of a heterogeneous solution-based assay for multicomponent analysis, what is the concentration of the target fungal ssPCR DNA that is used, and how do you manage the kinetics of the reaction such that the target reaches the probe in a time frame appropriate for a clinical assay?

Hollow gold nanospheres (HGNs) provide a tunable surface plasmon resonance from 550 to 820 nm by controlling their inner diameter and wall thickness. Although they have been used for biological imaging based on their optical properties in the near-infrared region, their surface-enhanced Raman scattering (SERS) performance has not been thoroughly studied. Herein, HGNs with different surface plasmon resonances were synthesized and functionalized with different Raman reporters. HGNs coupled with Raman reporters, on and off resonant with the laser excitation wavelength, were systematically interrogated in isolated and partially aggregated situations. HGNs with thicker shells generated higher SERS responses than thinner shells no matter whether they were isolated, or partially aggregated, or whether their surface plasmon resonances were resonant with the excitation wavelength or not. This study gives insight into the basis of the SERS properties for these kinds of materials.

The increasing popularity of surface plasmon resonance (SPR) and surface enhanced Raman scattering (SERS) sensor design based on nanotriangle or nanohole arrays, and the possibility to manufacture substrates at the transition between these plasmonic substrates, makes them ideal candidates for the establishment of structure-property relationships. This work features near diffraction-limited Raman images and FDTD simulations of nanotriangle and nanohole arrays substrates, which clearly demonstrate that the localization of the hot spot on these SERS substrates is significantly influenced by the ratio of diameter/periodicity (D/P). The experimental and simulation data reveal that the hot spots are located around nanotriangles (D/P = 1), characteristic of localized SPR. Decreasing the D/P ratio to 0.75-0.7 led to the creation of nanohole arrays, which promoted the excitation of a propagating surface plasmon (SP) delocalized over the metal network. The optimal SERS intensity was consistently achieved at this transition from nanotriangles to nanoholes, for every periodicity (650 nm to 1.5 μm) and excitation wavelength (633 and 785 nm) investigated, despite the presence or absence of a plasmonic band near the laser excitation. Further decreasing the D/P ratio led to excitation of a localized SP located around the rim of nanohole arrays for D/P of 0.5-0.6, in agreement with previous reports. In addition, this manuscript provides the first evidence that the hot spots are positioned inside the hole for D/P of 0.4, with the center being the region of highest electric field and Raman intensity. The compelling experimental evidence and FDTD simulations offer an overall understanding of the plasmonic properties of nanohole arrays as SERS and SPR sensors, which is of significant value in advancing the diversity of applications from such surfaces.

Surface-enhanced (resonance) Raman spectroscopy (SE(R)RS) holds great promise for the in vivo detection of multiple disease markers. Nanotags consisting of a metallic nanoparticle decorated with reporter molecules encapsulated in either an inert or biofunctionalized shell, for inactive or active targeting, have been developed. To improve the tissue depth from which the signal can be detected, it is preferable to operate with excitation in the near-infrared wavelengths; however, this reduces the inherent Raman signal intensity. The signal strength can be reestablished by matching the absorbance of the nanoparticle with the laser excitation. However, nanoparticles must get physically larger to support absorbances in the near-infrared region, which can have an adverse affect on cellular uptake. In this paper we compare the use of silver nanoparticles with plasmon absorbances at longer wavelengths with clusters (2–4 nanoparticles) formed from much smaller nanoparticles which support so-called “hot spots”. We ...

Single-molecule detection by surface-enhanced resonance Raman scattering (SERRS) spectroscopy has been demonstrated for a variety of molecules. The detection of single molecules that do not have a resonance contribution, SERS, has been shown in the case of adenine. However, when colloidal particles isolated on planar substrates are used as the enhancing medium, the presence of anomalous signals significantly complicates the analysis of the spectra. Selection of a silver colloid that minimizes these spurious signals should improve the ultra-sensitive detection of non-resonant single molecules by SERS. A range of silver colloids, prepared by different methods, were investigated with respect to their activity and stability. Minimal anomalous signals were obtained from hydroxylamine-reduced silver colloids, which suggests that this colloid will be better for ultra-sensitive SE(R)RS experiments compared to the more common citrate- and borohydride-reduced silver colloids.

Surface-enhanced Raman scattering (SERS) and surface-enhanced resonance Raman scattering (SERRS) can provide positive identification of an analyte or an analyte mixture with high sensitivity and selectivity. Better understanding of the theory and advances in the understanding of the practice have led to the development of practical applications in which the unique advantages of SERS/SERRS have been used to provide effective solutions to difficult analytical problems. This review presents a basic theory and illustrates the way in which SERS/SERRS has been developed for practical use.

Surface enhanced raman scattering (SERS) based molecular diagnostic assays for the detection of specific DNA sequences have been developed in recent years to compete with the more common fluorescence based approaches. Current SERS assays either require time-consuming separation steps that increase assay cost and can also increase the risk of contamination or they are negative assays, where the signal intensity decreases in the presence of target DNA. Herein, we report a new separation free SERS assay with an increase in signal intensity when target DNA is present using a specifically designed SERS primer. The presence of specific bacterial DNA from Staphylococcus epidermidis was detected using polymerase chain reaction (PCR) and SERS and indicates a new opportunity for exploration of SERS assays requiring minimal handling steps.

Surface enhanced Raman scattering (SERS) "hot spots" are the regions where the electromagnetic field is significantly enhanced, resulting in much greater SERS activity than other areas. Therefore, the engineering and characterization of "hot spots" have attracted much attention. Herein, we have synthesized nanoworms formed by connecting hollow gold nanospheres and investigated their composition as well as their SERS properties, including their potential for simultaneous analysis of multiple species. The three-dimensional nanostructures that led to different SERS activities were investigated using correlated optical/SERS and SEM imaging. Gold nanoworms with hollow nanosphere segments and partial tube formation were confirmed. All highly SERS-active structures were found to be three-dimensional arrays consisting of inter-/intrananoworm interactions; no individual nanospheres were found to give significant SERS signal under the experimental conditions. The major SERS contribution was found to be the electromagnetic coupling effect within the three-dimensional arrays and the localized surface plasmon resonance of the nanostructure was found to have a minimal effect. This study gives insight into the basis of enhancement for these nanoworm structures and adds to the growing body of evidence in relation to nanostructures and surface enhancement of Raman scattering. © 2011 American Chemical Society.

The first Human Papilloma Virus (HPV) genotyping assay using surface-enhanced Raman scattering (SERS) is reported. Validated PCR primers were used to generate amplification products from plasmids, a control cell line and clinical specimens enabling subsequent identification of specific HPV genotypes using type specific probes across six channels.

This chapter looks at various aspects of quantitative DNA analysis using surface enhanced resonance raman scattering

A novel wide-field approach for the real-time Surface Enhanced Raman Scattering (SERS) imaging of multiple silver nanoparticle clusters suspended in solution is described. This method enables direct correlation of the SERS activity of a single nanoparticle aggregate and its size through measurement of the cluster diffusion coefficient and can also be performed in a high-throughput basis. As a first demonstration, we investigate the salt-induced aggregation of silver nanoparticles in the presence of a reporter tag molecule, which has a high affinity for the nanoparticle surface. In addition to tracking individual particles, direct comparison of Rayleigh and SERS videos of the same colloid solution enabled measurement of the fraction of individual clusters that are SERS active and the dependence of this value on the relative concentration of the tag molecule. Furthermore, given the ability to also rapidly profile any nonuniformity in particle size distributions, we expect this approach will not only provide a new tool for the fundamental understanding of SERS but also significantly contribute to the development of an array of emerging nanoparticle-enhanced biomolecule and imaging detection platforms.

The control of the assembly of nanostructures of dye-coded oligonucleotide−silver nanoparticle (DOSN) conjugates (silver nanoparticles cofunctionalized with thiol modified DNA and a Raman reporter molecule) in a sandwich assay format with single base discrimination in an unmodified target oligonucleotide is reported. Rational placement of a single base mismatch in the 18 base duplex formed between target and DOSN conjugates completely controls the hybridization event, preventing or allowing nanostructure formation. The assembly process was monitored using UV−vis spectrometry and surface-enhanced resonance Raman scattering (SERRS). These two supporting analysis techniques show that there is an initial formation of small, highly SERRS active assemblies followed by the formation of larger superaggregates. The rapid increase in SERRS intensity obtained from DOSN conjugate hybridization has been utilized for the near-immediate discrimination of a single base mismatch using SERRS. This report highlights the exq...

We present a multi-component optimisation strategy for a range of commonly used Ag colloids as surface-enhanced Raman scattering (SERS) spectroscopy substrates. The concentration-dependent interactions of a wide range of parameters, including colloid and aggregating agent species, were considered in order to achieve optimal SERS enhancements. Few papers in the literature discuss the optimisation of these parameters, never mind multi-component optimisation, and suboptimal responses result in SERS not being utilised to its true capabilities. Significant differences in enhancement factor were observed as a consequence of colloid-aggregating agent interactions and these are shown to be analyte specific. Both the cation and anion of the aggregating agent were found to play an important role in the optimisation process. We show that through the optimisation of experimental conditions, the reliability and applicability of SERS can be significantly improved.

SERRS (surface-enhanced resonance Raman scattering) is a vibrational spectroscopy which allows extremely sensitive and selective detection of labelled DNA sequences with detection limits which rival, and in most cases surpass, that of fluorescence. SERRS relies on a visible chromophore adsorbing on to an enhancing surface. DNA itself is not SERRS-active, as it lacks a suitable visible chromophore and has poor adsorption properties on to the surfaces used for enhancement. The surface normally used for enhancement in these sorts of studies are metallic nanoparticles and, through modification of DNA probes by the addition of suitable SERRS labels, signals can be obtained that are highly sensitive and very selective. The aggregation state of the nanoparticles is critical to the sensitivity, and, in the present paper, we show how straightforward detection of labelled DNA probes can be achieved using SERRS in a quantitative manner and with a variety of different commercially available labels. In a second approach, we show how the properties of aggregation to turn on the SERRS effect can be exploited through DNA hybridization to give identification of a particular DNA sequence. This approach lends itself to closed-tube formats and is a promising way forward for molecular diagnostics using SERRS.

A series of surface-enhanced resonance Raman scattering (SERRS) based probes for the detection of lipase activity are reported. A number of novel SERRS-active 8-hydroxylquinolinyl azo dyes have been prepared and via synthetic esterification or subsequent enzymatic hydrolysis at the 8-hydroxyl position the SERRS signal can be "switched" on or off. In the first instance, the technique has been demonstrated for the successful detection of lipase from Pseudomonas cepacia, and these new compounds offer a limit of detection of 0.2 ng mL-1 enzyme, up to a 100-fold lower limit than observed for benzotriazolyl dyes used in previous studies. The chemical synthesis is straightforward and allows for facile introduction of a wide range of different masking groups, using commonly known synthetic methodologies. The potential for multiplexing analysis of enzyme activity using this technology is presented within.

Surface-enhanced resonance Raman scattering (SERRS) from silver nanoparticles using 514.5-nm excitation has been shown to offer huge potential for applications in highly sensitive multiplexed DNA assays. If the technique is to be applied to real biological samples and integrated with other methods, then the use of gold nanoparticles and longer wavelengths of excitation are desirable. The data presented here demonstrate that dye-labeled oligonucleotide sequences can be directly detected by SERRS using gold nanoparticles in a quantitative manner for the first time. The performance of gold and silver nanoparticles as SERRS substrates was assessed using 514.5-, 632.8-, and 785-nm excitation and a range of 13 commercially available dye-labeled oligonucleotides. The quantitative response allowed the limit of detection to be determined for each case and demonstrates that the technique is highly effective, sensitive, and versatile. The possibility of excitation at multiple wavelengths further enhances the multiplexing potential of the technique. The importance of effectively combining the optical properties of the nanoparticle and the dye label is demonstrated. For example, at 632.8-nm excitation, the dye BODIPY TR-X and gold nanoparticles make a strong SERRS combination with very little background fluorescence. This study allows the choice of nanoparticle and dye label for particular experimental setups, and significantly expands the applicability of enhanced Raman scattering for use in many disciplines.

A number of silver particles and aggregates of particles were studied using surface enhanced resonance Raman spectroscopy (SERRS), high resolution transmission electron microscopy (HRTEM) and electron energy-loss spectroscopy (EELS). The SERRS mapping/TEM collage method developed previously in our group allows each SERRS active or inactive species to be reliably identified and analysed by each of the techniques in three different instruments. Our aim is to correlate SERRS activity, particle microstructure, chemical composition and electronic properties of each species to gain an insight into the enhancement mechanism. To date, our findings do not reveal any clear link between particle microstructure and SERRS activity. Additionally, the direction of the polarisation of the incident excitation or the presence of interparticle junctions between aggregated particles was not correlated with SERRS activity. However, spectral variations in the EELS data from structurally similar particles and SERRS active and inactive particles suggest that each species is chemically/electronically distinct. Differences in the spectra of single particles, dimers and clusters were also observed. Further analysis of the data, including extraction of the complex dielectric function from the EELS data, will provide an insight into the relationship between these observations and SERRS activity.

Beads labelled using surface enhanced resonance Raman scattering (SERRS) are highly sensitive and specific tags, with potential applications in biological assays, including molecular diagnostics. The beads consist of a nucleus containing dye labelled silver-nanoparticle aggregates surrounded by a polymer core. The nuclei generate strong SERRS signals. To illustrate the coding advantage created by the sharp, molecularly specific SERRS signals, four specially designed SERRS dyes have been used as labels and three of these have been combined in a multiplex analysis. These dyes use specific groups such as benzotriazole and 8-hydroxyquinoline to improve binding to the surface of the silver particles. The aggregation state of the particles is held constant by the polymer core, this nucleus also contains many dye labels, yielding a very high Raman scattering intensity for each bead. To functionalise these beads for use in biological assays an outer polymer shell can be added, which allows the attachment of oligonucleotide probes. Oligonucleotide modified beads can then be used for detection of specific oligonucleotide targets. The specificity of SERRS will allow for the detection of multiple targets within a single assay.

The detection of dye labelled DNA by surface enhanced resonance Raman scattering (SERRS) is reported. The dye labels used are commercially available and have not previously been used as SERRS dyes. Detection limits using two excitation frequencies were determined for each label. This expands the range of labels which can be used for surface enhanced resonance Raman scattering with silver nanoparticles.

Polymer films developed for distance detection, containing dye-coated silver particles for ultra-sensitive analysis using surf ace-enhanced resonance Raman scattering (SERRS), identified the need for effective SERRS labels that interact strongly with the metal surfaces. Many dyes that are currently used for SERRS can be displaced from the surface owing to the relatively weak surface attachment, and therefore they do not adhere strongly enough to the surface for many practical applications, i.e. to withstand incorporation into environments such as paints, resins and polymers. Rhodamine dyes are very effective in SERRS under ideal laboratory conditions, as shown by the detection of single molecules. The synthesis of 19-[4-(benzotriazole-5-ylsulfamoyl)-2-methylphenyl]-6-diethylaminoxanthen-3-ylidene]diethylammonium (benzotriazole rhodamine B, BTRB), which was designed to give much stronger surface adhesion, was evaluated using SERRS in comparison with two commercially available rhodamine dyes, rhodamine 6G and rhodamine B. The increased strength of interaction with the roughened metal surface was shown to increase the versatility of BTRB in terms of the choice of aggregating agent and also the type of sample prepared. Therefore, the modification of rhodamine dyes to incorporate a benzotriazole group widens the range of practical applications for which they are suitable for detection using SERRS.

Track it down: A recognized surface-enhanced Raman scattering (SERS) nanotag signal was monitored from a thin, dispersed layer of bisphosphonate-functionalized nanotags on a bone sample, through a 20 mm thick specimen of porcine muscle tissue by surface-enhanced spatial offset Raman spectroscopy (SESORS; see picture). The result demonstrates the great potential for non-invasive in vivo bisphosphonate drug tracking.

Surface enhanced Raman scattering (SERS) and surface enhanced resonance Raman scattering (SERRS) from a silver colloid suspension are compared using a dye designed to bond strongly to a silver surface. Titration of the dye into a silver colloid suspension caused aggregation in a controlled manner without an aggregating agent being added. Concentrations of dye equivalent to between 5 x 10(-9) and 10(-3) M in the final dilution before adsorption to the silver were used. The results suggest that nionolayer coverage of the surface occurs at approximately 10(-6) M. Above this concentration, the suspensions are less stable, and the relationship between intensity and concentration is complex. Below this concentration, three main regions can be identified by electronic absorption spectroscopy. At dye concentrations up to 7.5 x 10(-8) M, there is little evidence of aggregation, although there are changes in the spectra ascribed here. to surface changes caused by dye adsorption. Between 7.5 x 10(-8) M and 2.5 x 10(-7) M, a well-defined small aggregate appears to occur and above 2.5 x 10(-7) M larger less well-defined aggregates form. SERRS gave linear concentration dependence below 7.5 x 10(-8) M suggesting scattering from single particles. A changeover region occurs close to where the first evidence of aggregation is detected by electronic spectroscopy, and at higher concentrations up to about monolayer coverage a second linear region was obtained. SERS below the concentration at which aggregation is detected by electronic spectroscopy was weak and difficult to obtain. At higher concentrations, the SERS gradients are steeper and the maximum enhancement observed is within a factor of 4 of that obtained in SERRS. The study shows that there is a different mechanism in SERRS compared to SERS with single particle enhancement being much greater in SERRS.

We report the manufacture of ordered silver and copper nanorod arrays for surface-enhanced Raman scattering using oblique angle deposition (OAD) on prepatterned polymer sheets. It was found that the patterned polymer substrate defined nucleation sites which guided subsequent growth of nanorods. Enhanced surface-enhanced Raman spectroscopy (SERS) intensities of the Raman probe molecule trans-1,2-bis(4-pyridyl)ethylene (BPE) were found for Ag arrays on polymer, up to about 10 times that of the Ag-silica control. The SERS response of Ag nanorod arrays of different structures was investigated alongside results obtained from discrete dipole approximation simulations. This revealed that narrow gaps between nanorods, formed by guided nucleation during OAD, were responsible for this dramatic enhancement. Ordered Cu nanorod arrays were also successfully fabricated, producing a SERS intensity about 3 times that of Cu on silicon for both BPE and another Raman probe - rhodamine B isothiocyanate (RBITC) - highlighting the potential of this large-scale, low-cost, SERS-active substrate.

Spherical and monodispersed silver nanoparticles (AgNPs) are ideal for fundamental research as the contribution from size and shape can be accounted for in the experimental design. In this paper a seeded growth method is presented, whereby varying the concentration of sodium borohydride-reduced silver nanoparticle seeds, different sizes of stable spherical nanoparticles with a low polydispersity nanoparticles are produced using hydroquinone as a selective reducing agent. The surface-enhanced Raman scattering (SERS) enhancement factor for each nanoparticle size produced (17, 26, 50, and 65 nm) was then assessed using three different analytes, rhodamine 6G (R6G), malachite green oxalate (MGO) and thiophenol (TP). The enhancement factor gives an indication of the Raman enhancement effect by the nanoparticle. Using non-aggregated conditions and two different laser excitation wavelength (633 nm and 785 nm) it is shown that an increase in particle size results in an increased enhancement for each analyte used.