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Biofilms are complex environments where matrix effects from components such as extracellular polymeric substances and proteins can strongly affect SERS performance. Here the interactions between SERS-enhancing Ag and Au particles were studied using ex situ biofilms (es-biofilms), which were more homogenous than in situ biofilm samples. This allowed systematic quantitative studies, where samples could be accurately diluted and analysed, to be carried out. Strong signals from intrinsic marker compounds were found for the Pseudomonas aeruginosa and Staphylococcus aureus extracted es-biofilms, which the standard addition method showed were due to 2 × 10–3 mol dm−3 pyocyanin or the equivalent of 1 × 10–4 mol dm−3 adenine, respectively. The es-biofilms hindered aggregation of Ag colloids more than Au but for both Au and Ag nanospheres the presence of es-biofilm reduced SERS signals through a combination of poorer aggregation and blocking of surface sites. For Ag, the effect of lower aggregation was to reduce the signals by a factor of ca. 2×, while site blocking gave a further 10× reduction for adenine. Similar results were found for Au nanospheres with adenine, although these particles gave low enhancement with pyocyanin. Nanostars were found to be unaffected by reduced aggregation and also showed lower site blocking effects, giving more reproducible signals than those from aggregated particles, which compensated for their lower enhancement factor. These results provide a rational basis for selecting enhancing substrates for use in in situ studies, where the further complexity means that it is important to begin with well-understood and controllable enhancing media.

Electron/proton transfers in water proceeding from ground/excited states are the elementary reactions of chemistry. These reactions of an iconic class of molecules─polypyridineRu(II)─are now controlled by capturing or releasing three of them with hosts that are shape-switchable. Reversible erection or collapse of the host walls allows such switchability. Some reaction rates are suppressed by factors of up to 120 by inclusive binding of the metal complexes. This puts nanometric coordination chemistry in a box that can be open or shut as necessary. Such second-sphere complexation can allow considerable control to be exerted on photocatalysis, electrocatalysis, and luminescent sensing involving polypyridineRu(II) compounds. The capturing states of hosts are symmetry-matched to guests for selective binding and display submicromolar affinities. A perching complex, which is an intermediate state between capturing and releasing states, is also demonstrated.

DNA/RNA synthesis precursors are especially vulnerable to damage induced by reactive oxygen species occurring following oxidative stress. Guanosine triphosphates are the prevalent oxidized nucleosites, which can be misincorporated during replication, leading to mutations and cell death. Here, we present a novel method based on micro-Raman spectroscopy, combined with ab initio calculations, for the identification, detection, and quantification of low concentrations of oxidized nucleotides. We also show that the Raman signature in the terahertz spectral range (< 100 cm$^{-1}$) contains information on the intermolecular assembly of guanine in tetrads, which allows to further boost the oxidative damage detection limit. Eventually, we provide evidence that similar analyses can be carried out on samples in very small volumes at very low concentrations by exploiting the high sensitivity of Surface Enhanced Raman Scattering combined with properly designed superhydrophobic substrates. These results pave the way for employing such advanced spectroscopic methods for quantitatively sensing the oxidative damage of nucleotides in the cell., 11 pages, 7 figures

SERS is currently being explored as a rapid method for identification of bacteria but variation in the experimental procedures has resulted in considerable variation in the spectra reported for a range of bacterial species. Here, we show that mixing bacteria with a conventional citrate-reduced silver colloid (CRSC) and drying the resulting suspension yield highly reproducible spectra. These signals were due to intracellular components released when the structure of the bacteria was disrupted during sample preparation. This reproducibility allowed us to examine the effects of variables that do not arise in SERS of simple solutions but Saveare relevant in studies of bacteria. These included growth phase and biological variation, which occurred when the same bacterial isolates were cultured under nominally identical conditions on different days. It was found that even under optimal standardized conditions the effect of differences in experimental parameters such as growth phase was very large in some bacterial species but insignificant in others. This suggests that it is important to avoid drawing general conclusions about bacterial SERS based on studies using small numbers of samples. Similarly, discrimination between bacterial species was straightforward when a small number of isolates with distinct spectral features were investigated; however, this became more challenging when more bacterial species were included, as this increased the possibility of finding different species of bacteria with similar spectra. These observations are important because they clearly delineate the challenges that will need to be addressed if SERS is to be used for clinical applications.

Surface-enhanced Raman spectroscopy (SERS) is an emerging analytical technique for chemical analysis, which is favourable due to its combination of short measurement time, high sensitivity and molecular specificity. However, the application of SERS is still limited, largely because in real samples the analyte is often present in a complex matrix that contains micro/macro particles that block the probe laser, as well as molecular contaminants that compete for the enhancing surface. Here, we show a simple and scalable spray-deposition technique to fabricate SERS-active paper substrates which combine sample filtration and enhancement in a single material. Unlike previous spray-deposition methods, in which simple colloidal nanoparticles were sprayed onto solid surfaces, here the colloidal nanoparticles are mixed with hydroxyethyl cellulose (HEC) polymer before application. This leads to significantly improved uniformity in the distribution of enhancing particles as the film dries on the substrate surface. Importantly, the polymer matrix also protects the enhancing particles from air-oxidation during storage but releases them to provide SERS enhancement when the film is rehydrated. These SERS-paper substrates are highly active and a model analyte, crystal violet, was detected down to 4 ng in 10 μL of sample with less than 20% point-by-point signal deviation. The filter paper and HEC effectively filter out both interfering micro/macro particles and molecular (protein) contaminants, allowing the SERS-paper substrates to be used for SERS detection of thiram in mud and melamine in the presence of protein down to nanogram levels without sample pre-treatment or purification.

Self-assembly at water-oil interfaces has been shown to be a cheap, convenient and efficient route to obtain densely packed layers of plasmonic nanoparticles which have small interparticle distances. This creates highly plasmonically active materials that can be used to give strong SERS enhancement and whose structure means that they are well suited to creating the highly stable, reproducible and uniform substrates that are needed to allow routine and accurate quantitative SERS measurements. A variety of methods have been developed to induce nanoparticle self-assembly at water-oil interfaces, fine tune the surface chemistry and adjust the position of the nanoparticles at the interface but only some of these are compatible with eventual use in SERS, where it is important that target molecules can access the active surface unimpeded. Similarly, it is useful to transform liquid plasmonic arrays into easy-to-handle free-standing solid films but these can only be used as solid SERS substrates if the process leaves the surface nanoparticles exposed. Here, we review the progress made in these research areas and discuss how these developments may lead towards achieving rational construction of tailored SERS substrates for sensitive and quantitative SERS analysis.

Building easy-to-handle bulk materials with nanoproperties is crucial for many nanotechnology-based real-world applications. Here, we describe a simple one-pot method based on nanoparticle self-assembly of pickering emulsions and in situ polymer deposition for preparing particles consisting of a rigid micro-polymer core covered in exposed surface layers of nanoparticles, which we have named nano-micro-particles (NMPs). Unlike simple colloids, these NMPs can be filtered off from the aqueous suspensions in which they are prepared and dried to form free-flowing powders, which most importantly, retain the properties of the constituent nanoparticles in the surface layer. These NMPs can be stored for extended periods but then used either in the dry state or be re-suspended into liquid media as required. The preparation method is very general and can be readily extended to assemble various types of nanoparticles regardless of their material composition or morphology. In addition, functional components, such as magnetic particles or fluorescent tags, can be encapsulated within the polymer core. This method is a platform technology for building nanoparticles into bulk materials with nano-functionalities tailored toward real-life applications. This is illustrated with examples of the preparation of NMPs suitable for rapid and low-cost on-site water monitoring and remediation.

In colloidal SERS only analytes that can spontaneously adsorb onto nanoparticles are detected. Therefore, considerable effort has been placed on modifying the surface properties of colloidal particles, particularly Ag particles, to promote the absorption of “difficult” analytes which do not spontaneously adsorb to as-prepared nanoparticles. In contrast, much less attention has been paid to the role which the identity of the underlying metal plays in the absorption since it is widely believed that the chemical properties of Ag and Au are very similar. This leads to the assumption that molecules which do not adsorb to Ag, such as hydrocarbons, will also not adsorb to aggregated Au colloids for SERS measurements. Here, we challenge this common perception by showing that SERS detection of “difficult” aromatic targets such as naphthalene, trinitrotoluene and 3,4-methylenedioxymethamphetamine which cannot be achieved even at >10-3 M concentrations with bare aggregated Ag colloids is possible at ≥10-8 M with unmodified aggregated Au colloids. For naphthalene and 3,4-methylenedioxymethamphetamine the detection limit obtained in this work with bare citrate-capped Au particles exceeds the previous best limit of detection obtained with surface-modified nanoparticles by an order of magnitude.

Thin, flexible, surface-active, polystyrene-based, optically transparent films, embedded with a coating of commercially sourced titanium dioxide nanoparticles (Evonik P25), are made by coupling protonated TiO2 particles with an anionic phase transfer agent (tetraphenylborate), to create an ion-paired species that is drawn to a water/dichloromethane (DCM) interface to form a monolayer. The latter is subsequently embedded in a thin polystyrene (PS) film, typically 2.5 μm thick, by allowing the DCM to evaporate. The resulting clear TiO2 Surface-Exposed Nanoparticle (TiO2-SEN) thin plastic films are characterised using scanning electron microscopy (SEM) and found to have 25.3 ± 5.4 nm TiO2 nanoparticles exposed to the air on one side and PS on the other. The photocatalytic activity of these films is demonstrated using a number of different tests including: the photo-oxidation of 4-chlorophenol (4-CP) and methylene blue (MB) and the photoreduction of resazurin (Rz) and MB. In most of these tests the photoactivity of the film is more than double compared to that of a commercial photocatalytic film, Activ™.

Often chemical analysis of solid materials begins with dissolving the sample in a solvent but this is undesirable, particularly if the physical form is important. In principle surface-enhanced Raman spectroscopy (SERS) should allow detection of solid analytes and offers attomolar sensitivity combined with molecular specificity. SERS requires the target molecules to sit in plasmonic hot-spots, which are normally nanojunctions, just a few nm across. This means that solid samples normally need to be dissolved in a solvent so they can diffuse into the enhancing region. Here, we show that SERS spectra of picograms of solid analytes can be directly obtained by pressing them into a flexible SERS substrate with a dense field of exposed nanojunction hot-spots anchored on its surface. We demonstrate that this can be a powerful tool for straightforward and non-destructive forensic analysis of layered materials (crossing ink lines), solid explosives and illicit drugs as well as for studying previously intractable samples such as pharmaceutical co-crystals, whose important solid state structure is lost when they are dissolved.

In-situ surface-enhanced Raman spectroscopy of the headspace above cultures of 6 bacterial species allowed sensitive and selective detection of characteristic bands from chemisorbed methyl sulphide. This marker compound is created by dissociation of adsorbed dimethyl disulphide (DMDS) on the surface of the Au or Ag nanoparticle (NP) films which are used as the enhancing media. DMDS is a well-known fermentative metabolite of bacteria and was also detected here by GC-MS of the headspace of bacteria cultures. Kinetic binding plots of media spiked with DMDS and of live cultures, both showed that the more rapid adsorption of DMDS onto Au based substrates made them more suitable for the rapid detection of bacteria than Ag based substrates. E. coli DH5α was chosen for the proof-of-principal experiments. For this micro-organism, the sensitivity limit was found to be the detection of bacteria in the headspace of a 1.5 x 10⁷ CFU/ml culture. Under our conditions, this corresponds to detection 15 minutes after inoculation of the growth medium, but it will depend on the CFU/ml of the initial inoculum used. Since the metabolites are only produced by viable bacteria, antibiotic (gentamicin) treatment stopped the normal signal growth of the marker peak. This work is a promising step towards rapid bedside detection of bacterial infections and rapid screening of antibiotics against model cultures.

Therapeutic drug monitoring (TDM) is important for many therapeutic regimens and has particular relevance for anticancer drugs which often have serious effects and whose optimum dosage can vary significantly between different patients. Many of the features of surface enhanced (resonance) Raman spectroscopy (SE(R)RS) suggest it should be very suitable for TDM of anticancer drugs and some initial studies which explore the potential of SE(R)RS for TDM of anticancer drugs have been published. This review brings this work together in an attempt to draw some general observations about key aspects of the approach, including the nature of the substrate used, matrix interference effects and factors governing adsorption of the target molecules onto the enhancing surface. There is now sufficient evidence to suggest that none of these pose real difficulties in the context of TDM. However, some issues, particularly the need to carry out multiplex measurements for TDM of combination therapies, have yet to be addressed.

Self-assembly of colloidal nanoparticles at water-oil interfaces offers an efficient way to construct multi-dimensional arrays. Self-assembly is generally induced by using adsorbing molecular “modifiers” or co-solvants to remove the nanoparticles’ surface charge. Here, it is shown that CTAB, which is commonly used in bulk-quantities in colloidal synthesis, can induce self-assembly of negatively charged colloidal nanoparticles at water-oil interfaces, even at sub-micromolar levels but it does this by providing charge-screening rather than removing the surface charge. Since this is a physical effect, CTAB can promote assembly of nanoparticles regardless of their morphology or material composition. In the specific case of nanoparticles which allow CTAB to adsorb, such as Au, the self assembly mechanism switches from charge-screening to chemical-adsorption as the concentration is increased. This both explains previous observations of spontaneous interfacial assembly and opens up further possibilities for deliberately constructing functional nanoparticle-arrays without the need for additional modifiers or co-solvents.

Current strategies for the treatment of superficial non-melanoma skin cancer (NMSC) lesions include topical imoquimod, 5-fluorouracil, and photodynamic therapy. Although these treatments are effective, burning pain, blistering, and dermatitis have been reported as frequent side effects, making these therapies far from ideal. Plasmonic materials have been investigated for the induction of hyperthermia and use in cancer treatment. In this sense, the effectiveness of intratumorally and systemically injected gold nanorods (GnRs) in inducing cancer cell death upon near-infrared light irradiation has been confirmed. However, the in vivo long-term toxicity of these particles has not yet been fully documented. In the present manuscript, GnRs were included in a crosslinked polymeric film, evaluating their mechanical, swelling, and adhesion properties, moreover, their ability to heat up neonatal porcine skin (such as a skin model) upon irradiation was tested. Inclusion of GnRs into the films did not affect mechanical or swelling properties. GnRs were not released after film swelling, as they remained entrapped in the polymeric network, moreover, films did not adhere to porcine skin, altogether showing the enhanced biocompatibility of the material. GnR-loaded films were able to heat up the skin model over 40 &deg, C, confirming the potential of this system for non-invasive local hyperthermia applications.

Experimental results obtained in different laboratories world‐wide by researchers using surface‐enhanced Raman scattering (SERS) can differ significantly. We, an international team of scientists with long‐standing expertise in SERS, address this issue from our perspective by presenting considerations on reliable and quantitative SERS. The central idea of this joint effort is to highlight key parameters and pitfalls that are often encountered in the literature. To that end, we provide here a series of recommendations on: a) the characterization of solid and colloidal SERS substrates by correlative electron and optical microscopy and spectroscopy, b) on the determination of the SERS enhancement factor (EF), including suitable Raman reporter/probe molecules, and finally on c) good analytical practice. We hope that both newcomers and specialists will benefit from these recommendations to increase the inter‐laboratory comparability of experimental SERS results and further establish SERS as an analytical tool., Parameters and pitfalls: Key parameters and pitfalls that are often encountered in surface‐enhanced Raman scattering (SERS) are highlighted. Good analytical practice is proposed to increase the inter‐laboratory comparability of experimental SERS results and further establish SERS as an analytical tool.

Au/Ag colloids aggregated with simple salts are amongst the most commonly used substrates in surface-enhanced (resonance) Raman spectroscopy (SE(R)RS). However, salt-induced aggregation is a dynamic process, which means that SE(R)RS enhancements vary with time and that measurements therefore need to be taken at a fixed time point, normally within a short time-window of a few minutes. Here, we present an emulsion templated method which allows formation of densely-packed quasi-spherical Au/Ag colloidal aggregates. Since the particles in the product aggregates retain their weakly adsorbed charged ligands and the ionic strength remains low these charged aggregates resist further aggregation while still providing intense SE(R)RS enhancement which remains stable for days. This eliminates a major source of irreproducibility in conventional colloidal SE(R)RS measurements and paves the way for SE(R)RS analysis in complex systems, such as protein-rich bio-solutions where conventional aggregated colloids fail.

Microbial fouling is a costly issue, which impacts a wide range of industries, such as healthcare, food processing, and construction industries, and improved strategies to reduce the impact of fouling are urgently required. Slippery liquid-infused porous surfaces (SLIPSs) have recently been developed as a bioinspired approach to prevent antifouling. Here, we report the development of slippery, superhydrophilic surfaces by infusing roughened poly(vinyl chloride) (PVC) substrates with phosphonium ionic liquids (PILs). These surfaces were capable of reducing viable bacterial adherence by Staphylococcus aureus and Pseudomonas aeruginosa by >6 log10 cfu mL−1 after 24 h under static conditions relative to control PVC. Furthermore, we report the potential of a series of asymmetric quaternary alkyl PILs with varying alkyl chain lengths (C4−C18) and counteranions to act as antimicrobial agents against both Gram +ve and Gram −ve bacteria and illustrate their potential as antimicrobial alternatives to traditional fluorinated lubricants commonly used in the synthesis of SLIPSs.

The photocatalytic efficiency of TiO2 can be increased by using co-catalysts, such as metal nanoparticles, which act as electron sinks to suppress the recombination of photogenerated electron–hole pairs. The main challenge in preparing such systems is to create intimate contact between the metal and the TiO2 surface while still maintaining control over the morphology and distribution of the metal nanoparticles in the TiO2 matrix. Here lightweight TiO2 films are prepared by assembling a layer of TiO2 nanoparticles onto a thin polymer support, followed by physical vapor deposition of metal nanoparticles onto the TiO2 surface. Importantly the fabrication does not involve any chemical modifications to the surface of NPs, which allows spontaneous formation of strong chemical bonds between deposited metal and TiO2. Systematic optimization of this process gives materials 6× more catalytically active than the parent TiO2 films and up to 18× more catalytically active than commercial photoactive TiO2 glass. Moreover, the transparent, flexible, and robust polymer support enables the product films to be easily used for repeated photocatalytic reactions. Since the whole fabrication process is scalable and highly reproducible, this approach provides new opportunities for controlled synthesis of a new family of practical high-performance metal- semiconductor hybrid photocatalysts.

Rapid and sensitive methods to detect DNA lesions are essential in order to understand their role in carcinogenesis and for potential diagnosis of cancers. The 8-nitroguanine DNA lesion, which is closely associated with inflammation-induced cancers, has been characterised for the first time by surface-enhanced Raman spectroscopy (SERS). This lesion has been studied as the free base, as well as part of a dinucleotide and oligodeoxynucleotides (ODNs) at 5 different excitation wavelengths in the range 785-488 nm. All nitrated samples produced distinctly different spectra from their control guanine counterparts, with nitro bands being assigned by DFT calculations. Additional resonance enhancement was observed at the shorter excitation wavelengths, these SERRS measurements allowed the detection of one nitrated guanine in over 1,300 bases. In addition, SER(R)S can be used to detect whether the unstable lesion is covalently attached to the ODN or has been released by hydrolytic depurination.

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 data presented in this article is related to the research article entitled “A One-Pot Method for Building Colloidal Nanoparticles into Bulk Dry Powders with Nanoscale Magnetic, Plasmonic and Catalytic Functionalities” (Ye et al., 2019) The data shows the hydrophobicity of the nanoparticle (NP) building blocks used for constructing NMPs obtained through contact angle measurements, along with the effect of NP hydrophobicity on the stability of the parent Pickering emulsions. SEM data of the morphology of NMPs is presented. Finally, a mathematical model is presented to predict the average diameter of NMPs produced via different experimental parameters. Keywords: Promoter, Emulsion, Self-assembly, Nano-powder

Here, we present surface-enhanced Raman data for the calculation of signal uniformity and enhancement factor in SENSERS (surface-exposed nanoparticle sheet enhanced Raman spectroscopy). SEM was used to characterize the microstructure of the solid sample. The interaction between the solid sample and surface-exposed nanoparticle sheet was characterized using SERS and SEM. Based on these data a “skin” versus “sheet” type calculation method was used to calculate the magnitude of Raman signal enhancement within SENSERS. The data presented in this article is related to the research article entitled “Pressing Solids Directly Into Sheets of Plasmonic Nanojunctions Enables Solvent-Free Surface-Enhanced Raman Spectroscopy” (Xu et al., 2018).

Rapid and accurate identification of pathogens in CF could ensure prompt treatment with the most appropriate antibiotic; potentially improving outcomes and shortening hospital stays. As traditional culture methods for detecting bacteria are time-consuming there is a growing interest in SERS as a novel culture-free technique that produces a whole-organism spectroscopic fingerprint at high speed. Bacterial isolates including Pseudomonas aeruginosa (n=32), Staphylococcus aureus (n=5), Streptococcus pneumoniae (n=5) were incubated for 6 h at 37 °C/180 r.p.m., with a starting optical density (OD) of 0.15. After adjustment of the OD to 0.3, bacterial cells were harvested by centrifugation at 9000 rcf for 3 min and washed three times with dH2O. Bacterial pellets were mixed with citrate reduced silver colloid (CRSC) and dried. Spectra were recorded (4×10 s at 785 nm) and analysed within GRAMS/Al using Principal Component Analysis (PCA). Spectra of P. aeruginosa isolates (n=32) were separated into two distinct groups; the spectra of one group (n=12) was dominated by the pigment pyocyanin with vibrational brands present at 1350, 1492, 1598 and 1615 cm-1. The other group (n=20) had characteristic vibrational bands at 661, 735 and 800 cm-1 which correspond to guanine, adenine and uracil, respectively. S. aureus has a main characteristic band at 735 cm-1 and S. pneumoniae has a characteristic band present at 480 cm-1. Bacterial species clustered separately when analysed by PCA. Reproducible and distinguishable SERS spectra of bacterial isolates were obtained, and it was possible to differentiate between different bacterial species using PCA. These results suggest SERS has the potential to rapidly detect bacteria.

Pharmacological therapy of osteoporosis reduces bone loss and risk of fracture in patients. Modulation of bone mineral density cannot explain all effects. Other aspects of bone quality affecting fragility and ways to monitor them need to be better understood. Keratinous tissue acts as surrogate marker for bone protein deterioration caused by oestrogen deficiency in rats. Ovariectomised rats were treated with alendronate (ALN), parathyroid hormone (PTH) or estrogen (E2). MicroCT assessed macro structural changes. Raman spectroscopy assessed biochemical changes. Micro CT confirmed that all treatments prevented ovariectomy-induced macro structural bone loss in rats. PTH induced macro structural changes unrelated to ovariectomy. Raman analysis revealed ALN and PTH partially protect against molecular level changes to bone collagen (80% protection) and mineral (50% protection) phases. E2 failed to prevent biochemical change. The treatments induced alterations unassociated with the ovariectomy; increased beta sheet with E2, globular alpha helices with PTH and fibrous alpha helices with both ALN and PTH. ALN is closest to maintaining physiological status of the animals, while PTH (comparable protective effect) induces side effects. E2 is unable to prevent molecular level changes associated with ovariectomy. Raman spectroscopy can act as predictive tool for monitoring pharmacological therapy of osteoporosis in rodents. Keratinous tissue is a useful surrogate marker for the protein related impact of these therapies.The results demonstrate utility of surrogates where a clear systemic causation connects the surrogate to the target tissue. It demonstrates the need to assess broader biomolecular impact of interventions to examine side effects.

Thermo-chemical conversion is a promising technology for the recycle of waste plastics, as it can produce high-value products such as carbon nanotubes (CNTs) and hydrogen. However, the low yield of CNTs is one of the challenges. In this work, the addition of Mn (0 wt.%, 1 wt.%, 5 wt.%, and 10 wt.%) to Fe-based catalyst to improve the production of CNTs has been investigated. Results show that the increase of Mn content from 0 wt.% to 10 wt.% significantly promotes CNTs yield formed on the catalyst from 23.4 wt.% to 32.9 wt.%. The results show that Fe-particles in the fresh catalysts are between 10−25 nm. And the addition of Mn in the Fe-based catalyst enhanced the metal-support interactions and the dispersion of metal particles, thus leading to the improved catalytic performance in relation to filamentous carbon growth. In addition, the graphitization of CNTs is promoted with the increase of Mn content. Overall, in terms of the quantity and quality of the produced CNTs, 5 wt.% of Mn in Fe-based catalyst shows the best catalytic performance, due to the further increase of Mn content from 5 wt.% to 10 wt.% led to a dramatic decrease of purity by 10 wt.%.

Two-dimensional metal nanoparticle arrays are normally constructed at liquid–oil interfaces by modifying the surfaces of the constituent nanoparticles so that they self-assemble. Here we present a general and facile new approach for promoting such interfacial assembly without any surface modification. The method use salts that have hydrophobic ions of opposite charge to the nanoparticles, which sit in the oil layer and thus reduce the Coulombic repulsion between the particles in the organic phase, allowing the particles to sit in close proximity to each other at the interface. The advantage of this method is that because it does not require the surface of the particles to be modified it allows nonmetallic particles including TiO2 and SiO2 to be assembled into dense interfacial layers using the same procedure as is used for metallic particles. This opens up a route to a new family of nanostructured functional materials.

This study provides experimental and theoretical evidence that the coating of the inner surface of copper pipes with superhydrophobic (SH) materials induces a Cassie state flow regime on the flow of water. This results in an increase in the fluid's dimensionless velocity distribution coefficient, α, which gives rise to an increase in the apparent Reynolds number, which may approach the “plug flow state”. Experimental evidence from the SH coating of a classic unsteady-state flow system resulted in a significant decrease in the friction factor and associated energy loss. The friction factor decrease can be attributed to an increase in the apparent Reynolds number. The study demonstrates that the Cassie effects imposed by SH coating can be quantitatively shown to decrease the frictional resistance to flow in commercial pipes.

The potential of IR absorption and Raman spectroscopy for rapid identification of novel psychoactive substances (NPS) has been tested using a set of 221 unsorted seized samples suspected of containing NPS. Both IR and Raman spectra showed large variation between the different sub-classifications of NPS and smaller, but still distinguishable, differences between closely related compounds within the same class. In initial tests, screening the samples using spectral searching against a limited reference library allowed only 41% of the samples to be fully identified. The limiting factor in the identification was the large number of active compounds in the seized samples for which no reference vibrational data were available in the libraries rather than poor spectral quality. Therefore, when 33 of these compounds were independently identified by NMR and mass spectrometry and their spectra used to extend the libraries, the percentage of samples identified by IR and Raman screening alone increased to 76%, with only 7% of samples having no identifiable constituents. This study, which is the largest of its type ever carried out, therefore demonstrates that this approach of detecting non-matching samples and then identifying them using standard analytical methods has considerable potential in NPS screening since it allows rapid identification of the constituents of the majority of street quality samples. Only one complete feedback cycle was carried out in this study but there is clearly the potential to carry out continuous identification/updating when this system is used in operational settings.

Chili powder is a globally traded commodity which has been found to be adulterated with Sudan dyes from 2003 onwards. In this study, chili powders were adulterated with varying quantities of Sudan I dye (0.1–5%) and spectra were generated using near infrared reflectance spectroscopy (NIRS) and Raman spectroscopy (on a spectrometer with a sample compartment modified as part of the study). Chemometrics were applied to the spectral data to produce quantitative and qualitative calibration models and prediction statistics. For the quantitative models coefficients of determination ( R 2 ) were found to be 0.891–0.994 depending on which spectral data (NIRS/Raman) was processed, the mathematical algorithm used and the data pre-processing applied. The corresponding values for the root mean square error of calibration (RMSEC) and root mean square error of prediction (RMSEP) were found to be 0.208–0.851% and 0.141–0.831% respectively, once again depending on the spectral data and the chemometric treatment applied to the data. Indications are that the NIR spectroscopy based models are superior to the models produced from Raman spectral data based on a comparison of the values of the chemometric parameters. The limit of detection (LOD) based on analysis of 20 blank chili powders against each calibration model gave 0.25% and 0.88% for the NIR and Raman data, respectively. In addition, adopting a qualitative approach with the spectral data and applying PCA or PLS-DA, it was possible to discriminate between adulterated chili powders from non-adulterated chili powders.

peer-reviewed Osteoporosis is a common disease characterised by reduced bone mass and an increased risk of fragility fractures. Low bone mineral density is known to significantly increase the risk of osteoporotic fractures, however, the majority of non-traumatic fractures occur in individuals with a bone mineral density too high to be classified as osteoporotic. Therefore, there is an urgent need to investigate aspects of bone health, other than bone mass, that can predict the risk of fracture. Here, we successfully predicted association between bone collagen and nail keratin in relation to bone loss due to oestrogen deficiency using Raman spectroscopy. Raman signal signature successfully discriminated between ovariectomised rats and their sham controls with a high degree of accuracy for the bone (sensitivity 89%, specificity 91%) and claw tissue (sensitivity 89%, specificity 82%). When tested in an independent set of claw samples the classifier gave 92% sensitivity and 85% specificity. Comparison of the spectral changes occurring in the bone tissue with the changes occurring in the keratin showed a number of common features that could be attributed to common changes in the structure of bone collagen and claw keratin. This study established that systemic oestrogen deficiency mediates parallel structural changes in both the claw (primarily keratin) and bone proteins (primarily collagen). This strengthens the hypothesis that nail keratin can act as a surrogate marker of bone protein status where systemic processes induce changes.

The potential of surface-enhanced Raman scattering (SERS) spectroscopy in both laboratory and field analyses depends on the reliable formation of so-called SERS hot spots, such as those formed during gold or silver nanoparticle aggregation. Unfortunately such aggregates are not stable in solution because they typically grow until they precipitate. Here we describe the use of low-molecular-weight hydrogels formed through pH-triggered self-assembly that occurs at a rate that well matches the rates of aggregation of Au or Ag colloids, allowing them to be trapped at the SERS-active point in the aggregation process. We show that the colloid-containing gels give SERS signals similar to the parent colloid but are stable over several months. Moreover, lyophilized gels can be stored as dry powders for subsequent use in the analyses of gases and dissolved analytes by contact with either solutions or vapors. The present system shows how the combination of pH-switchable low-molecular-weight gelators and pH-induced colloid aggregation can be combined to make a highly stable, low-cost SERS platform for the detection of volatile organic compounds and the microvolume analysis of solutions.

To address the question of whether the SERS signals of ss-DNA are simply combinations of the signals from the individual bases that comprise the sequence, SERS spectra of unmodified ss-DNA sequences were obtained using a hydroxylamine-reduced Ag colloid aggregated with MgSO4. Initially, synthetic oligodeoxynucleotides with systematic structural variations were used to investigate the effect of adding single nucleobases to the 3′ terminus of 10-mer and 20-mer sequences. It was found that the resulting SERS difference spectra could be used to identify the added nucleobases since they closely matched reference spectra of the same nucleobase. Investigation of the variation in intensity of an adenine probe which was moved along a test sequence showed there was a small end effect where nucleobases near the 3′ terminus gave slightly larger signals but the effect was minor (30%). More significantly, in a sample set comprising 25-mer sequences where A, T or G nucleobases were substituted either near the centres of the sequences or the 5′ or 3′ ends, the SERS difference spectra only matched the expected form in approximately half the cases tested. This variation appeared to be due to changes in secondary structure induced by altering the sequences since uncoiling the sequences in a thermal pre-treatment step gave difference spectra which in all cases matched the expected form. Multivariate analysis of the set of substitution data showed that 99% of the variance could be accounted for in a model with just three factors whose loadings matched the spectra of the A, T, and G nucleobases and which contained no positional information. This suggests that aside from the differences in secondary structure which can be eliminated by thermal pre-treatment, the SERS spectra of the 25-mers studied here are simply the sum of their component parts. Although this means that SERS provides very little information on the primary sequence it should be excellent for the detection of post-transcription modifications to DNA which can occur at multiple positions along a given sequence.

Large (10 × 10 cm) sheets of surface-enhanced Raman spectroscopy (SERS) active polymer have been prepared by stabilising metal nanoparticle aggregates within dry hydroxyethylcellulose (HEC) films. In these films the aggregates are protected by the polymer matrix during storage but in use they are released when aqueous analyte droplets cause the films to swell to their gel form. The fact that these "Poly-SERS" films can be prepared in bulk but then cut to size and stored in air before use means that they provide a cost effective and convenient method for routine SERS analysis. Here we have tested both Ag and Au Poly-SERS films for use in point-of-care monitoring of therapeutic drugs, using phenytoin as the test compound. Phenytoin in water could readily be detected using Ag Poly-SERS films but dissolving the compound in phosphate buffered saline (PBS) to mimic body fluid samples caused loss of the drug signal due to competition for metal surface sites from Cl- ions in the buffer solution. However, with Au Poly-SERS films there was no detectable interference from Cl- and these materials allowed phenytoin to be detected at 1.8 mg L-1, even in PBS. The target range of detection of phenytoin in therapeutic drug monitoring is 10-20 mg L-1. With the Au Poly-SERS films, the absolute signal generated by a given concentration of phenytoin was lower for the films than for the parent colloid but the SERS signals were still high enough to be used for therapeutic monitoring, so the cost in sensitivity for moving from simple aqueous colloids to films is not so large that it outweighs the advantages which the films bring for practical applications, in particular their ease of use and long shelf life.

The rise in popularity of electronic cigarettes and the associated new legislation concerning e-liquids has created a requirement for a rapid method for determining the nicotine content of e-liquids in the field, ideally at the point of sale. Here we have developed a rapid method based on surface-enhanced Raman spectroscopy (SERS) with Au colloids and an isotope-labeled nicotine (d4-nicotine) internal standard for the measurement/quantification of samples which contain 10s of mg mL−1 nicotine in a complex viscous matrix. This method is novel within the area of SERS because it uses high dilution (ca. 4000×) in the sample preparation which dilutes out the effects of the viscous glycerin/glycerol medium and any flavouring or colouring agents present but still allows for very accurate calibration with high reproducibility. This is possible because the nicotine concentration in the e-liquids (≤24 mg mL−1) is of several orders of magnitude above the working range of the SERS measurement. This method has been tested using a portable Raman spectrometer and a very large set of 42 commercial e-liquids to check that there is no matrix interference associated with different manufacturers/flavourings/colouring agents etc. Finally, as an alternative to determining the nicotine concentration by measuring peak heights in the spectra, the concentration was also estimated by comparing the sample spectra with those of a set of standard samples which were prepared at known concentrations and held in a spectral library file in the spectrometer. This simple approach allows the concentration to be estimated without any complex data analysis and lends itself readily to a handheld Raman system which is typically designed to carry out library searching using the internal software for materials identification. Library searching against standards correctly classified 41 of the 42 test liquids as belonging to the correct concentration group. This high dilution SERS approach is suitable for the analysis of sample types that have reasonably high concentrations of analytes but suffer from matrix problems, and it therefore has broad potential for applications across food, pharmaceutical and nutraceutical areas.

2D arrays of metal nanoparticles formed at liquid-liquid interfaces have been fixed in situ to a thin polymer support to create freestanding large (cm2 ) composite films where the particles remain exposed rather than being trapped within the polymer. Applications of these flexible robust 2D nanoparticle arrays as sensors, thin film conductors, antimicrobial coatings, and dip-in catalysts are shown.

The first page of this article is displayed as the abstract., Rohit Chikkaraddy opened the discussion of the Introductory Lecture: Regarding quantifying the chemical enhancement, you showed a systematic change in the SERS enhancement for halide substituted molecules due to charge transfer from the metal. Is the extra enhancement due to an inherent increase in the Raman cross-section of the molecule? How do you go about referencing, as the charge transfer changes the vibrational frequency? Richard Van Duyne answered: The extra enhancement is not due to an increase in the Raman cross section, as that is ratioed out in the calculation of the enhancement factor. The charge transfer (CT) process does not transfer a complete electron, it is a fractional degree of CT. Thus the change in vibrational frequency is small. DFT calculations that provide eigenvectors allow one to reference the vibrational modes of the free molecule with those of the adsorbed molecule. Sylwester Gawinkowski asked: You have shown that the enhancement factor curve is redshifted relative to the plasmon resonance band and has a maximum at about 800 nm. This means that the SERS signal should be strongest for excitations in the near infrared spectral region. Why do most SERS reports, particularly related to single molecule SERS, have the excitation in the green or red spectral range and not in the near infrared?

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

Discussions.