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Surface-enhanced Raman spectroscopy (SERS) is a unique technique that allows us to detect samples in trace quantities. The spectral intensities of the characteristic Raman peaks of the analyte molecule are enhanced manifold in the presence of noble metal nanoparticles (NPs). The existence of NPs is necessary to couple the incident electromagnetic field with NPs through the localized surface plasmon resonance phenomenon, which primarily contributes to the enhancement of an SERS signal. The present work demonstrates the working of a paper-based SERS substrate to detect and quantify two pharmaceutical drugsâ€"paracetamol and aspirinâ€"in water. The proposed SERS substrate was obtained by drop-casting silver NPs over printing grade 100 grams per square meter (GSM) paper. 100 GSM denotes the class of paper where 100 grams of raw materials (cellulose) is used per square meter to manufacture the paper. The performance of the designed SERS substrate was initially evaluated with two Raman active samplesâ€"malachite green and rhodamine-6G. The applicability of the proposed SERS substrate was evaluated further through monitoring the Raman spectra of the two aforementioned pharmaceutical drugs in different field-collected water samples, thus establishing the reliability of the scheme in a real field environment. [ABSTRACT FROM AUTHOR]

Finding a low cost substrate for surface-enhanced Raman spectroscopy (SERS) yielding enhanced, reproducible Raman signal from Raman active samples has been a longstanding goal for researchers for years. Herein, we demonstrate the fabrication of such a SERS substrate from paper. The proposed paper-based SERS substrate was developed by attaching polyvinylpyrrolidone (PVP) capped silver nano-particles (AgNPs) to printing grade paper. The performance of the substrate has been evaluated for paper substrates of various grades (in grams per square meter; GSM). The usability of the developed substrate for detection of two Raman active samples—namely, malachite green (MG) and rhodamine6G (R6G)—is reported. In addition to these samples, the reproducibility of the designed substrate has been evaluated for 1,2-bis(4-pyridyl)ethylene (BPE); a good degree of reproducibility was observed. Finally, applicability of the proposed substrate for reliable detection of Raman signals from two more important samples—namely, glucose and urine—has been successfully demonstrated. [ABSTRACT FROM AUTHOR]

Surface enhanced Raman spectroscopy (SERS) is a powerful analytical technique that has found application in the trace detection of a wide range of contaminants. In this paper, we report on the fabrication of 2D silver nanodendrites, on silicon chips, synthesized by electrochemical reduction of AgNO3 at microelectrodes. The formation of nanodendrites is tentatively explained in terms of electromigration and diffusion of silver ions. Electrochemical characterization suggests that the nanodendrites do not stay electrically connected to the microelectrode. The substrates show SERS activity with an enhancement factor on the order of 106. Density functional theory simulations were carried out to investigate the suitability of the fabricated substrate for pesticide monitoring. These substrates can be functionalized with cyclodextrin macro molecules to help with the detection of molecules with low affinity with silver surfaces. A proof of concept is demonstrated with the detection of the herbicide 2-methyl-4-chlorophenoxyacetic acid (MCPA). [ABSTRACT FROM AUTHOR]

The appearance of the double-resonance substrate has promoted the application of surface-enhanced Raman scattering (SERS). By controlling the frequencies of the double resonances to match the excitation and Raman scattering frequencies, the detection of the object to be measured can be more effective. For the double-resonance substrate, while the resonance frequencies can be highly controllable, the electric field enhancement is also one of the important factors affecting the application in SERS. In this paper, we designed a metasurface composed of a nanoring dimer array, silica dielectric and gold film. The nanoring dimer array and gold film are separated by the silica dielectric to form a resonant cavity. The localized surface plasmon resonance generated in the nanoring dimer array is coupled with the cavity mode of the resonant cavity. Double Fano resonance with strong electric field enhancement is generated at the gap of the nanoring dimer. The electric field enhancement value can reach 100, which is an order of magnitude larger than that of the nanoring metasurface without the gap structure. The double Fano resonance peaks can be flexibly adjusted while maintaining large electric field enhancements by changing the following parameters: the period of the nanoring dimer array along the direction of the short axis, the ratio of the inner and outer radius of the nanoring and the length of the resonant cavity. Therefore, the proposed metasurface-enhanced Raman scattering substrate provides both the enhanced and tunable double Fano resonances necessary for high-sensitivity, high-selectivity and high-throughput detection. In addition, we proved that the length of the cavity can be determined by theoretical calculation, which avoids a lot of simulation processes. [ABSTRACT FROM AUTHOR]

In this paper, Au nanoparticles (AuNPs) are prepared using wet chemical reduction transfer of dense AuNPs film by self-assembly to the surface of Ag grating, which is inverted from the inner DVD after evaporation. The Ag grating/AuNPs self-assembly hybrid substrate commonly used in surface-enhanced Raman scattering (SERS) research is produced. The coupling effect between AuNP-AuNP and AuNPs-Ag slugs can evidently enhance the local electric field. Experimental results show that the hybrid SERS substrate can detect 10−9 M Rh6G, and the enhancement factor reaches 4.4 × 105. This small, cheap hybrid substrate has enormous potential in the field of SERS sensing. [ABSTRACT FROM AUTHOR]

Plasmonic nanostructures have important applications for surface-enhanced Raman chips, optical sensors, perfect absorbers, and so on. In this paper, we theoretically investigate the optical properties of a T-shaped dimer (TD) nanostructure and a TD with nanowire loads (TD/NL) nanostructure. By depositing the NLs around the TD, the optical property of the TD is significantly modified, and the extinction spectrum of composite TD/NL appears the splitting resonance peak and shows the asymmetric characteristic of Fano resonance due to the plasmon hybridization. Besides, a stronger electric field enhancement can be obtained in the composite TD/NL nanostructure, and the calculated results show the field enhancement effect of the dark mode in designed TD/NL nanostructure is three times than that in the TD nanostructure. Furthermore, the Fano resonance in TD/NL nanostructure reveals the narrow spectral linewidth and high quality factor, which is advantageous to optical refractive index sensors, and the corresponding sensing sensitivity is as high as 1083 nm RIU−1. [ABSTRACT FROM AUTHOR]

Accurate and rapid diagnosis of traumatic brain injury (TBI) is very important for high quality medical services. Nonetheless, the current diagnostic platform still has challenges in the rapid and accurate analysis of clinical samples. Here, we prepared a highly stable, repeatable and sensitive gold-plated silver core–shell nanowire (Ag@AuNWs) for surface-enhanced Raman spectroscopy (SERS) metabolic fingerprint diagnosis of TBI. The core–shell structure significantly enhanced SERS intensity and enables the direct detection of 10 μ l serum within seconds. The principal component analysis-linear discriminant analysis (PCA-LDA) and partial least squares-DA (PLS-DA) are used to evaluate the classification effect of this technology on TBI, respectively. The diagnosis accuracy rate of PCA-LDA and PLS-DA is 73.3% and 86.7% for diagnosing TBI, respectively. Consequently, the PLS-DA model is the optimal selection for distinguishing between the TBI and sham groups. This research will facilitate the application-oriented creation of novel materials with tailored structural designs and the formulation of innovative precision medical protocols in the imminent future. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to establish a method for easy operation, high sensitivity, strong anti-interference ability, and rapid quantitative detection of cardiac fatty acid-binding protein in acute myocardial infarction biomarkers, so that it can be quickly diagnosed at an early stage and provide a basis for further treatment. Based on the SERS principle, the traditional sandwich system generated by the reaction was captured by the streptavidin (SA) magnetic beads through the specific reaction of SA and biotin then enriched by the applied magnetic field. The enriched magnetic beads are subjected to Raman detection to achieve a process of quantitative detection of the antigen. The minimum detection limit of this study was 1.4490 ng ml−1, the recoveries were 97.36%–98.35%, and the relative standard deviations between batches and batches were less than 15%. There was no crossover between cTnI, D-dimmer and NT-proBNP. In addition to hemoglobin, the common interfering substances in serum and common anticoagulants do not interfere with the test results. Surface-enhanced Raman spectroscopy can quickly and accurately quantify the acute myocardial infarction marker H-FABP, which is easy to operate and strong in anti-interference ability. [ABSTRACT FROM AUTHOR]

A simple and rapid system based on Raman nanosphere (R-Sphere) immunochromatography was developed in this study for the simultaneous detection of Influenza A, B virus antigens on a single test line (T-line). Two types of R-Sphere with different characteristic Raman spectrum were used as the signal source, which were labeled with monoclonal antibodies against FluA, FluB (tracer antibodies), respectively. A mixture of antibodies containing anti-FluA monoclonal antibody and anti-FluB monoclonal antibody (capture antibody) was sprayed on a single T-line and goat anti-chicken IgY antibody was coated as a C-line, and the antigen solution with known concentration was detected by the strip of lateral flow immunochromatography based on surface-enhanced Raman spectroscopy (SERS). The T-line was scanned with a Raman spectrometer and SERS signals were collected. Simultaneous specific recognition and detection of FluA and FluB were achieved on a single T-line by analyzing the SERS signals. The findings indicated that the test system could identify FluA and FluB in a qualitative manner in just 15 minutes, with a minimum detection threshold of 0.25 ng ml−1, excellent consistency, and specificity. There was no interference with the other four respiratory pathogens, and it exhibited 8 times greater sensitivity compared to the colloidal gold test strip method. The assay system is rapid, sensitive, and does not require repetitive sample pretreatment steps and two viruses can be detected simultaneously on a single T-line by titrating one sample, which improves detection efficiency, and provide a reference for developing multiplexed detection techniques for other respiratory viruses. [ABSTRACT FROM AUTHOR]

High-sensitivity quantitative analysis of sepsis disease markers in circulating blood is essential for sepsis early diagnosis, rapid stratification, and interventional treatment. Herein, a high-sensitivity biosensor combining surface-enhanced Raman spectroscopy (SERS) and functionalized magnetic materials was developed to quantitatively detect interleukin-6 (IL-6), a glycoprotein disease marker closely related to sepsis. First, boronic acid-functionalized magnetic nanomaterials with high adsorption performance were synthesized by utilizing the branched polyethyleneimine to provide many binding sites for boronic acid. Under antibody-free conditions, dendrimer-assisted boronic acid-functionalized magnetic nanomaterials selectively capture glycoproteins in complex biological samples as bio-capture element. Then, a core–shell bimetallic material with plenty of 'hot spots' was designed and synthesized as the enhancement substrate. The 4-Mercaptobenzonitrile (4-MP) with a characteristic peak at 2224 cm−1 (Raman-silent region) was embedded as the Raman reporter to form a SERS immune probe with highly efficient electromagnetic enhancement effect, achieving specific recognition and high-sensitivity detection of IL-6 on bio-capture elements. Using this strategy for quantitative analysis of IL-6, a wide detection range (0.5–5000 pg ml−1) and a low detection limit (0.453 pg ml−1) were obtained. Moreover, this method exhibited excellent detection performance for IL-6 in human serum samples, demonstrating its potential promise in screening clinically relevant diseases. The biosensor presented here not only provides a novel and universally applicable sensing strategy for the enrichment and detection of trace glycoprotein disease markers, but also the application of a portable Raman spectrometer provides a more reliable experimental basis for the diagnosis and treatment of major diseases in the clinic or remote and deprived areas. [ABSTRACT FROM AUTHOR]

Metal nanogaps can confine electromagnetic field into extremely small volumes, exhibiting strong surface plasmon resonance effect. Therefore, metal nanogaps show great prospects in enhancing light–matter interaction. However, it is still challenging to fabricate large-scale (centimeter scale) nanogaps with precise control of gap size at nanoscale, limiting the practical applications of metal nanogaps. In this work, we proposed a facile and economic strategy to fabricate large-scale sub-10 nm Ag nanogaps by the combination of atomic layer deposition (ALD) and mechanical rolling. The plasmonic nanogaps can be formed in the compacted Ag film by the sacrificial Al2O3 deposited via ALD. The size of nanogaps are determined by the twice thickness of Al2O3 with nanometric control. Raman results show that SERS activity depends closely on the nanogap size, and 4 nm Ag nanogaps exhibit the best SERS activity. By combining with other porous metal substrates, various sub-10 nm metal nanogaps can be fabricated over large scale. Therefore, this strategy will have significant implications for the preparation of nanogaps and enhanced spectroscopy. [ABSTRACT FROM AUTHOR]

This work investigates the effect of plasma treatment on the morphology and composition of 15 × 15 mm2 silver nanoparticle (70–80 nm) thin films. The silver nanoparticles are deposited onto thermal silica (SiO2/Si) substrates by spin-coating, then they are treated by an open-to-air microwave argon plasma jet characterized by a neutral gas temperature of 2200 ± 200 K. Scanning electron microscopy analysis reveals that the number of isolated nanoparticles in the film sample decreases after exposure to multiple jet passes, and that polygonal structures with sharp corners and edges are produced. Similar structures with much rounder edges are obtained after conventional thermal annealing at temperatures up to 1300 K. Based on localized surface plasmon resonance analysis in the range of 350–800 nm, the main extinction band of silver nanoparticles experiences a redshift after treatment with the plasma jet or with thermal annealing. Moreover, both treatments induce surface oxidation of the nanoparticles, as evidenced by x-ray photoelectron spectroscopy. However, only the plasma-exposed samples exhibit a significant rise in the surface-enhanced Raman scattering (SERS) signal of oxidized silver at 960 cm−1. 29 × 29 μ m2 mappings of hyperspectral Raman IMAging (RIMA) and multivariate curve resolution analysis by log-likelihood maximization demonstrate that the SERS signal is controlled by large-scale micrometer domains that exhibit sharp corners and edges. [ABSTRACT FROM AUTHOR]

The surface-supported silver nanoparticles have been studied and applied in various applications. Many unique nanostructures have been introduced into this field to improve the functionalities of the surfaces depending on application purposes. We created featured silver nano-array surfaces by utilizing the solvent-mediated phase transition on the surface grafted with poly (acrylic) acids polymer chains and taking advantage of the low temperature of argon gas discharged plasma as a reducing agent. The applied solvents and grafted polymer chain densities affected the phase transition and thus determined the outcome of surface nano-array patterns. However, the total loaded silver ions on the surface affected silver nano-array structures at the sub-micron levels. The featured silver patterned surfaces made in the optimal conditions present a favorable surface-enhanced Raman spectroscopy enhancement as well as recyclability for detection re-usage. This novel method prepares tunable silver nanopatterned surfaces and provides a new approach to various potential applications. [ABSTRACT FROM AUTHOR]

Vertically coupled plasmonic structures have been widely used in optical applications due to its enhanced electromagnetic fields in the gaps between metallic nanostructures. In this paper, a large-scale vertically coupled structure composed of the Ag triangle array (AgTA) on Ag grating separated by a nanometric dielectric layer is fabricated by nanosphere lithography incorporated with photolithography. Thanks to the effective surface plasmon polaritons excitation on the Ag grating, a significant surface enhanced Raman spectroscopy (SERS) effect arises from a strongly enhanced local electric field within the tiny gaps between the AgTA and Ag grating, which is verified by experiment and theoretical simulations. The as-proposed SERS substrate exhibits a nice uniformity with the relative standard deviation of about 10.5%, leading to excellent reliability for Raman detection. The simple fabrication of the large-area, productive, and inexpensive vertically coupled plasmonic structure can be a potential candidate for SERS applications. [ABSTRACT FROM AUTHOR]

Surface enhanced Raman scattering (SERS) substrates with both high activity and long term chemical-stability have been expected in the practical application of the SERS-based detection. In this paper, Au–Ag bimetal nanocrystals are fabricated based on the template-etching reaction in the Ag nanocubes-contained cetylpyridinium chloride (CPC) aqueous solution via adding the HAuCl4 solution. The obtained nanocrystals are Au–Ag alloyed and hollow in structure. Further, it has been found that with the increasing Au/Ag molar ratio, the shape of the alloyed nanocrystals evolve from the truncated nanocubes to the hollow boxes and then nanocages, showing the ever red-shifting surface plasmon resonance from the visible to the infrared region. The formation of the alloyed hollow nanocrystals is attributed to the preferential dissolution of the Ag nanocubes induced by CPC selective adsorption and the three to one galvanic replacement reaction between Ag and Au atoms. Importantly, such Au–Ag alloyed hollow nanocrystals, especially the ones with a low Au/Ag atomic ratio, show both high SERS activity and long term environmental stability compared with pure Ag or Au nanocrystals, and are the ideal candidate for the SERS substrate with practical application value. This work not only demonstrates the nanofabrication route to the alloyed hollow nanocrystals with controllable shapes and tunable optical properties in a large region, but also presents highly active and chemically-stable SERS substrates for the practical SERS-based detection. [ABSTRACT FROM AUTHOR]

We propose an anti-scratch flexible surface-enhanced Raman scattering substrate with arrayed nanocavity microstructures fabricated by colloidal lithography. The nanocavity microstructure of the substrate can well protect the inner gold nanoparticles during wipe sampling. The prepared flexible substrate was able to detect 4-aminothiophenol (4-ATP) with a concentration down to 1 fM. Furthermore, the substrate was used to detect 6-BA residues on the surface of apples and bean sprouts through wipe sampling, which shows great potential in the field of rapid on-site detection, especially in the detection of pesticide residues on the surface of fruits and vegetables. [ABSTRACT FROM AUTHOR]

In the present work we report a simple, fast, reproducible and cheap methodology for surface enhanced Raman spectroscopy (SERS) substrate fabrication of silver dendritic nanostructures (prepared by electrodeposition) decorated with gold nanospheres by electrophoretic deposition. This is the first report where a metal dendritic nanostructure has been decorated with another type of metal nanoparticles by this technique. The decorated nanostructures were used directly as SERS substrate using 4-aminothiophenol (4-ATP) as analyte. The objective of the decoration is to create more hot-spots in order to detect the analyte in a lower concentration. Decorated nanodendrites had a detection limit one million times lower than bare silver nanodendrites and all the substrates showed an increase in the Raman intensity at concentrations below 1 nM; because this concentration corresponds to the threshold for the formation of a monolayer resulting in a triple mechanism of intensity increase, namely electric field, chemical factor and hot-spots. 4-ATP was detected in attomolar concentration, which is below 1 ppq, corresponding to an analytical enhancement factor in the order of 1015. [ABSTRACT FROM AUTHOR]

Herein, a novel microfluidic-biochip enabled with surface enhanced Raman spectroscopy (SERS) as a readout has been demonstrated for uric acid (UA) detection as point-of care (POC) device. Three different biochip designs (D1, D2 and D3) containing pillars in a microchannel with different bending ratios were conceived and optimized for various mixing parameters using a multiphysics simulation tool. The microchannel, integrated with pillars, provide pressure perturbation, sharp corners, and variation in bending ratio improves phase shift and mixing index. Subsequently the microfluidic-biochips were fabricated by a combination of photo-and soft-lithography, and bonding strength between two Polydimethylsiloxane substrates were found stable up to a flow rate of 1.8 ml minâˆ'1. Further to realize SERS activity in the microfluidic-biochip, cubic shape silver nanoparticles (AgNPs), with an average size ∼68 nm, were synthesized using poly-ol method. The SERS activity was optimized by simultaneously flowing AgNPs and crystal violet (CV) dye of 10âˆ'6M, with double inlet in the reservoir and highest sensitivity was achieved in the D3 biochip. Further, D3 biochip was employed for detection of extended concentrations of CV and UA. The enhancement factor limit of detection and relative standard deviation was found to be 2 Ă— 107, 8.9 Ă— 10âˆ'11 and 2.7% respectively for CV and 3.1 Ă— 103, 3.2 Ă— 10âˆ'7 and 2.9% respectively for UA. Interference of UA with lactic acid has been tested and device was able to detect signature peaks of both biomarkers up to 50 Ă— 10âˆ'9 M concentration. Thus, the developed microfluidic-biochip device has potential to be used in a POC setting for onsite detection of biomarkers. [ABSTRACT FROM AUTHOR]

Silver nanoparticles are one of the most extensively used metallic nanomaterials due to their unusual physical and chemical properties as well as their promising applications in a wide range of different fields. In this study, a non-thermal atmospheric pressure helium plasma jet was used to successfully synthesize silver nanoparticles with silver nitrate as a precursor and trisodium citrate as a capping agent. The browning of the solution after only 5 min of plasma irradiation is a result of the surface plasmon resonance (SPR) from the obtained silver nanoparticles. The SPR was confirmed by the presence of an absorption band in the visible range between 400 and 450 nm demonstrated in the UVâ€"vis spectra. The effect of different chemical parameters such as the concentration of silver nitrate and the concentration of citrate on the silver nanoparticles have been studied. These nanoparticles were further characterized using transmission electron microscopy and dynamic light scattering. Therefore, the plasma jet was advantageous to fast produce silver nanoparticles in friendly conditions. In addition, the used experimental setup allows further studies in different solvents conditions and with different capping agents. So, this methodology could be useful for the preparation of silver nanoparticles required for numerous applications such as bioactivity, catalysis, surface enhanced Raman scattering, and photonic. [ABSTRACT FROM AUTHOR]

Realization of thermally and chemically durable, ordered gold nanostructures using bottom-up self-assembly techniques are essential for applications in a wide range of areas including catalysis, energy generation, and sensing. Herein, we describe a modular process for realizing uniform arrays of gold nanoparticles, with interparticle spacings of 2 nm and above, by using RF plasma etching to remove ligands from self-assembled arrays of ligand-coated gold nanoparticles. Both nanoscale imaging and macroscale spectroscopic characterization techniques were used to determine the optimal conditions for plasma etching, namely RF power, operating pressure, duration of treatment, and type of gas. We then studied the effect of nanoparticle size, interparticle spacing, and type of substrate on the thermal durability of plasma-treated and untreated nanoparticle arrays. Plasma-treated arrays showed enhanced chemical and thermal durability, on account of the removal of ligands. To illustrate the application potential of the developed process, robust SERS (surface-enhanced Raman scattering) substrates were formed using plasma-treated arrays of silver-coated gold nanoparticles that had a silicon wafer or photopaper as the underlying support. The measured value of the average SERS enhancement factor (2 × 105) was quantitatively reproducible on both silicon and paper substrates. The silicon substrates gave quantitatively reproducible results even after thermal annealing. The paper-based SERS substrate was also used to swab and detect probe molecules deposited on a solid surface. [ABSTRACT FROM AUTHOR]

Recently, in-situ surface-enhanced Raman spectroscopy (SERS) is gradually becoming an important method for monitoring photocatalytic reaction processes, in which the quantification potential is a vital factor in determining whether this technology can be truly applied in the future. In order to improve the quantification performance of in-situ SERS and explore a precise operando Raman detection for photocatalytic reactions, an architecture of heterostructural Cu2O/ZnO/Ag nano round brush has been designed and discussed in this work. This structure is an integration of sensitive in-situ SERS sensor and high-efficiency photocatalyst, realizing real-time monitoring of photocatalytic reaction in a wide concentration range from 20 to 3 mg lâˆ'1. The coefficient of determination between different detection methods is beyond 0.86 in this range, implying the high-precise quantification of this platform. Comprehensive analysis on structure effect, SERS performance, photocatalytic property, electric filed characteristic, etc were all systematically made and discussed in detail for this platform. This work presents a precise preliminar real-time photocatalytic monitoring using in-situ SERS detection, which is a new attempt and also meaningful reference for other in-situ analytical technology. [ABSTRACT FROM AUTHOR]

Dual-functionality Au-on-Ag nanostructures (AOA) were fabricated on a silicon substrate by first immobilizing citrate-reduced Ag nanoparticles (Ag NPs, ∼43 nm in diameter), followed by depositing ∼7 nm Au nanofilms (Au NFs) via thermal evaporation. Au NFs were introduced for their catalytic activity in concave-convex nano-configuration. Ag NPs underneath were used for their significant enhancement factor (EF) in surface-enhanced Raman scattering (SERS)-based measurements of analytes of interest. Rhodamine 6G (R6G) was utilized as the Raman-probe to evaluate the SERS sensitivity of AOA. The SERS EF of AOA is ∼37 times than that of Au NPs. Using reduction of 4-nitrothiophenol (4-NTP) by sodium borohydride (NaBH4) as a model reaction, we demonstrated the robust catalytic activity of AOA as well as its capacity to continuously monitor via SERS the disappearance of reactant 4-NTP, emergence and disappearance of intermediate 4,4′-DMAB, and the appearance of product 4-ATP throughout the reduction process in real-time and in situ. [ABSTRACT FROM AUTHOR]

A photonic nanojet (PNJ) from a microcavity is a narrow and intense beam of light used to enhance the emerging electric field. Metal nanoparticles (NPs), on the other hand, confine a strong field in their vicinity due to the resonance of the free electrons with the incident field. A hybrid combination of a microcavity with a NP can drastically enhance the output field. In this work, a systematic numerical study of the microcavity-NP system has been carried out to investigate the effect of the shape of the metal NPs on the output field strength. The single and their dimer NPs with different dimer nanogaps with PNJ producing microcavity have been investigated. Splitting of the broad dipole mode of the NP has also been observed. As an application of this study, the surface enhanced Raman spectroscopy factor of the order of 107 has been estimated for nano-cube dimer NP-microcavity hybrid system. [ABSTRACT FROM AUTHOR]

A facile method of creating a sensitive and inexpensive superhydrophobic nanoporous anodic alumina (NAA) based surface-enhanced Raman spectroscopy (SERS) substrate is reported. A superhydrophobic NAA was created by coating polydimethylsiloxane on NAA via polymer evaporation technique which further coated with gold to fabricate NAA-based superhydrophobic SERS substrate. NAA and nanopatterned aluminum with varying pore properties were used for the SERS studies using rhodamine 6 G as the model analyte. The limit of detection was calculated for the SERS substrate and found to be as low as 146.3 pM. The analytical enhancement factor was found to be 6.9 Ă— 105 successfully demonstrating the potential use of NAA-based superhydrophobic substrate as a SERS substrate. The substrates displayed good spatial reproducibility with a relative standard deviation of 12.62%, demonstrating the potential use of such substrates in chemical and biological sensing applications. The method reported is general and provides a simple and cost-effective approach for generating efficient SERS platforms for trace molecular sensing. [ABSTRACT FROM AUTHOR]

The technology of surface-enhanced Raman scattering (SERS) has found many applications and may find more if it can possess both sensitivity and thermal stability. This paper reports a rational design of Ag nanorods to simultaneously achieve two competing goals: the sensitivity and the thermal stability of SERS substrates. The Ag nanorods are designed and synthesized using physical vapor deposition under the condition of glancing angle incidence. The working pressure of the vacuum chamber is controlled so the mean free path of depositing atoms is comparable to the dimension of the chamber, so as to grow Ag nanorods with small diameter, and small but clear separation for optimal SERS sensitivity. Such Ag nanorods are further capped with Al2O3 on their top surfaces to reduce the diffusion-induced coarsening at high temperatures, and thereby to improve the thermal stability for SERS detections. Meanwhile, since the side surfaces of Ag nanorods are not coated with oxides in this approach, the SERS sensitivity is largely preserved while good thermal stability is achieved. [ABSTRACT FROM AUTHOR]

Metal film over nanosphere (MFON) metasurfaces have numerous applications, specifically as nanosensors for bio and chemical detection. Additionally, their interesting optical properties have also attracted the attention of many research groups. In this work, we study the influence of the metallic underlayer on the surface-enhanced Raman scattering (SERS) effect of the MFON structure. Two sets of MFON on silicon and mirror substrates were prepared for SERS measurement with rhodamine 6G. Experimental results show that the mirror layer boosts the SERS signal by two to five times. Finite difference time domain simulation was performed to gain insights into this improvement. Numerical results show that metallic underlayer helps to increase the concentration of the electric field at the hot spots. Moreover, it reflects the Raman signal via the extraordinary optical transmission channel of the MFON structure, improving the back-scattered Raman signal collection efficiency. Both of these effects can contribute to the increase of the SERS signal in agreement with the experimental results. More importantly, it provides an additional tool to tailor the optical properties of MFON metasurfaces. [ABSTRACT FROM AUTHOR]

We developed a rapid synthesis method for monodispersed Auâ€"Ag alloy nanosponges (NSs) with high density of ‘hotspots’ for near-infrared surface enhanced Raman scattering (NIR-SERS) by a selective laser-irradiation melting and chemical dealloying process. Au@Ag coreâ€"shell nanocubes were first in situ converted into solid alloyed Auâ€"Ag nanospheres by a rapid laser irradiation igniting quick fusion and quenching process within two minutes. The alloyed Auâ€"Ag nanospheres transformed into Auâ€"Ag alloy NSs after treated by a chemical dealloying process. Different from traditional thermal annealing, it thus can effectively avoid the heat fusion between nanoparticles, and maintain the alloyed Auâ€"Ag nanospheres and NSs in high monodispersity. Importantly, due to the strong plasmonic coupling in nanopores (pore size less than 10 nm), the obtained Auâ€"Ag alloy NSs show a broad and intense localized surface plasmon resonances absorption ranging from visible to near-Infrared region (500â€"1200 nm). The accessibly open structures for absorbing targets and high-density of ‘NIR-hotspots’ endow the Auâ€"Ag alloy NSs substrate with superior sensitivity in NIR-SERS detection of 4-aminothiophenol with an enhancement factor of ∼107. This work not only provides a simple pathway for rapid preparation of NIR-SERS substrate for biosensing, but also might open up a new horizon for fabricating spongy nanostructures with other elements. [ABSTRACT FROM AUTHOR]

We report the fabrication of low cost highly structured silver (Ag) capped aluminium (Al) nanorods (NRs) as surface enhanced Raman spectroscopy (SERS) substrate utilising the glancing angle deposition technique. The nano-capping of silver onto the Al NRs can concentrate the local electric field within the minimal volume that can serve as hotspots. The average size of the Ag nanocaps was 50 nm. The newly proposed nanoporous Ag capped Al NRs as SERS substrate could detect the Raman signal of rhodamine 6G (R6G) up to 10−15 molar concentration. The significant enhancement in the Raman signal of 107 was achieved for Ag capped Al NRs considering R6G as a probe molecule. Using the developed SERS substrate, we recorded Raman spectra for Escherichia coli bacteria with its concentration varying from 108 colony forming units per ml (CFU ml−1) up to 102 CFU ml−1. All the reported Raman spectra were acquired by a portable handheld Raman spectrometer. Hence, this newly proposed low cost, effective SERS substrate can be used commercially for the onsite detection of clinical pathogens. The 3D finite difference time domain simulation model was performed for Ag capped Al nanostructure to understand the generation of hotspots. The simulated results show excellent agreement with the experimental results. We fabricated uncapped Ag nanorods of similar dimensions and performed the experimental measurements and simulations for comparison. We found a significant enhancement in Ag capped Al NRs compared to the long Ag NRs. The description of the Raman signal enhancement has been elaborated. [ABSTRACT FROM AUTHOR]

Molecular fingerprints revealed by Raman techniques show great potential for biomedical applications, like disease diagnostic through Raman detection of tumor markers and other molecules in the cell membrane. However, SERS substrates used in membrane molecule studies produce enhanced Raman spectra of high variability and challenging band assignments that limit their application. In this work, these drawbacks are addressed to detect membrane-associated hemoglobin (Hbm) in human erythrocytes through Raman spectroscopy. These cells are incubated with silver nanoparticles (AgNPs) in PBS before Raman measurements. Our results showed that AgNPs form large aggregates in PBS that adhered to the erythrocyte membrane, which enhances Raman scattering by molecules around the membrane, like Hbm. Also, deoxyHb markers may allow Hbm detection in Raman spectra of oxygenated erythrocytes (oxyRBCs). Raman spectra of oxyRBCs incubated with AgNPs showed enhanced deoxyHb signals with good spectral reproducibility, supporting the Hbm detection through deoxyHb markers. Instead, Raman spectra of oxyRBCs showed oxyHb bands associated with free cytoplasmic hemoglobin. Other factors influencing Raman detection of membrane proteins are discussed, like both z-position and dimension of the sample volume. The results encourage membrane protein studies in living cells using Raman spectroscopy, leading to the characterization and diagnostic of different pathologies through a non-invasive technique. [ABSTRACT FROM AUTHOR]

We report on the experimental observation of mirror-enhanced directional surface-enhanced Raman scattering (SERS) from a self-assembled monolayer of molecules coupled to a nanowire-nanoparticle (NW-NP) junction on a mirror in a remote excitation configuration. Placing the NW-NP junction on a metallic mirror generates multiple gap plasmon modes that have unique momentum space-scattering signatures. We perform Fourier plane imaging of the SERS from the NW-NP on a mirror to understand the effect of multiple hotspots on molecular emission. We systematically study the effect of the ground plane on the directionality of emission from the NW-NP junction and show that the presence of a mirror drastically reduces the angular spread of emission. The effect of multiple hotspots in the geometry on the directionality of the molecular emission is studied using 3D numerical simulations. The results presented here will have implications in understanding plasmon hybridization in the momentum space and its effects on molecular emission. [ABSTRACT FROM AUTHOR]

This study demonstrated highly-ordered metallic nanotube arrays (MeNTAs) with a precisely controlled geometric shape to promote surface-enhanced Raman scattering (SERS). Using both simulation and experimental methods, we designed and fabricated MeNTAs with nanotube geometries that possess a large surface area to absorb probe molecules as well as geometric features capable of inducing hot spots for SERS enhancement. The proposed top-down wafer-scale lithographic and sputter-deposition process is a simple and cost-effective approach to the fabrication of 1 mm × 1 mm MeNTA at room temperature. Simulation results of nanotubes with various materials (Au, Ag, and Cu), diameters (100–1500 nm), geometric shapes (circle, equilateral triangle and square) and triangle corner curvatures (ranging from 0 to 300 nm) identified Ag triangles with sharp tips as the geometry best suited to SERS enhancement. The SERS spectra of crystal violet molecules generated from the Ag MeNTAs verified the patterns observed in computational simulations, wherein the effects of MeNTA on SERS decreased with an increase in the size of the nanotubes. Enhancement factor of 1.06 × 109 was obtained from our triangular Ag MeNTA, confirming its efficacy as an ultrahigh sensitivity SERS-active substrate. [ABSTRACT FROM AUTHOR]

In this paper, we report the tunable and enhanced SERS activity of magneto-plasmonic Ag–Fe3O4 nanocomposites that are synthesized by a one pot method. Crystal violet (CV), rhodamine 6 G (R6G) and 4-mercaptobenzoic acid (4-MBA) molecules are used to investigate the SERS optical activity of Ag–Fe3O4 nanocomposites under different external magnetic fields (1500, 2000, 2500, 3500 and 5000 gauss). The experimental results demonstrate the enhanced Raman effects that can be obtained by increasing the magnitude of external magnetic field. This is because the electromagnetic hot spots located between the neighboring Ag–Fe3O4 nanocomposites can be tuned by utilizing the external magnetic field. The bigger density of the hot-spots and amplitude of the electric field in the hot-spot are responsible for the enhanced SERS effect. The detection limit of CV molecule can be at least down to 10−9 M. The spectra measurements of hemoglobin adsorbed on the Ag−Fe3O4 nanocomposites under different external magnetic fields are also performed to explore its bio-applications. Finite element method (FEM) is used to simulate the local electromagnetic field distribution in Ag–Fe3O4 nanocomposites, revealing the SERS enhanced mechanism is determined mainly by the near field enhanced electromagnetic field. Due to its tunable and enhanced properties, Ag–Fe3O4 nanocomposites are expected to be promising SERS substrates for chemical and biological sensing applications. [ABSTRACT FROM AUTHOR]

Vertically coupled plasmonic structure is of great interest for surface-enhanced Raman scattering (SERS). In this paper, a large-area reproducible SERS substrate is fabricated and demonstrated by a vertically coupled structure composed of Ag triangle arrays on Ag films separated by a nanometric dielectric layer. This metal-insulator-metal (MIM) nanostructure has broadband resonance covering both the laser excitation and Stokes frequencies. Thanks to the convenience of controlling the gap distance by thin dielectric film, the SERS substrate is optimized to yield the best enhancement. The SERS enhancement factor is estimated to be 5.8 × 106 for on-resonant pumping with a 532 nm laser. The uniformity and reproducibility of the SERS substrate are also demonstrated. Our results pave the way for rational design of sensitive SERS substrates and harmless exciting SERS signals. [ABSTRACT FROM AUTHOR]

In this paper, we demonstrate a high-performance surface-enhanced Raman scattering (SERS) substrate based on high-density ordered Ag@Al2O3 nanobowl arrays. By ion beam etching (IBE) the anodized aluminum oxide (AAO) and subsequent Ag coating, ordered Ag@Al2O3 nanobowl arrays were created on the Si substrate. Unlike the ‘hot spots’ generated between adjacent metallic nanostructures, the Ag@Al2O3 nanobowl introduced ‘hot spots’ on the metal boundary of its hemispherical cavity. Based on the analysis of SERS signals, the optimized SERS substrate of Ag@Al2O3 nanobowl arrays had both high sensitivity and large-area uniformity. A detection limit as low as 10−10 M was obtained using chemisorbed p-thiocresol (p-Tc) molecules, and the SERS signal was highly reproducible with a small standard deviation. The method opens up a new way to create highly sensitive SERS sensors with high-density ‘hot spots’, and it could play an important role in device design and corresponding biological and food safety monitoring applications. [ABSTRACT FROM AUTHOR]

Flexible, transparent and mechanically robust surface enhanced Raman scattering (SERS)-active substrates is currently the most attractive research focus in the field of Raman detection, and also a powerful analysis and identification technique in the biological research. Herein, we introduced a low-cost and large-scale method to fabricate flexible and transparent AgNPs/WPU plasmonic metafilm with monolayer-island phase nanostructures based on silver nanoparticles (AgNPs) and waterborne polyurethane emulsion (WPU) film. The obtained AgNPs/WPU plasmonic metafilm demonstrated excellent SERS sensitivity, signal uniformity and reproducibility, and the SERS substrates could still maintain excellent stability even after being bent or stretched over 100 cycles. The detection concentration was as low as 10–9 M with 4-Mercaptobenzoic acid (4-MBA) as probe molecule, and the enhancement factor was high to 2.2 × 107. More importantly, the flexibility and adhesivity of AgNPs/WPU plasmonic metafilm could be directly conformal coverage on the apple surface for in situ detection of thiram residue, and the detection limit was as low as 9.0165 ng cm−2. This versatile AgNPs/WPU plasmonic metalfilm would be a promising SERS substrate for the detection of pesticide residue in chemical and biological applications. [ABSTRACT FROM AUTHOR]

The surface-enhanced Raman spectroscopy (SERS) has attracted much attention due to the powerful capability of quantificational analysis. Nowadays, most of the enhancement effect by SERS substrate is provided by the 'hot spots' occupying relatively small space. When the amount of analyte is too low, it is difficult to ensure that all the probe molecules can be placed into the 'hot spots', which is a headache in SERS quatification. In order to solve this problem, we have developed a structure of CuO nanowires/Ag nanoparticles with wettability capacity difference, which can aggregate molecules in water and oil simultaneously under two different mechanisms. The limit of detection and enhancement factor of this structure are estimated as 10−15 M and 1.55 × 1011 respectively (for rhodamine 6G, R6G). In a proof-in-principle experiment of sewage detection, it successfully achieved the aggregation and additional enhancement of both the R6G molecules in aqueous solution and thiuram molecules in toluene, realizing efficient and accurate Raman detection. [ABSTRACT FROM AUTHOR]

Gold bipyramid (GBP) nanoparticles are promising for a range of biomedical applications, including biosensing and surface-enhanced Raman spectroscopy, due to their favorable optical properties and ease of chemical functionalization. Here we report improved synthesis methods, including preparation of gold seed particles with an increased shelf life of ∼1 month, and preparation of GBPs with significantly shortened synthesis time (< 1 h). We also report methods for the functionalization and bioconjugation of the GBPs, including functionalization with alkanethiol self-assembled monolayers (SAMs) and bioconjugation with proteins via carbodiimide cross-linking. Binding of specific antibodies to the nanoparticle-bound proteins was subsequently observed via localized surface plasmon resonance sensing. Rabbit IgG and goat anti-Rabbit IgG antibodies were used as a model system for antibody-antigen interactions. As-synthesized, SAM-functionalized, and bioconjugated bipyramids were characterized using scanning electron microscopy, UV–vis spectroscopy, zeta potential, and dynamic light scattering. [ABSTRACT FROM AUTHOR]

Hybrid noble metal-semiconductor oxide nanostructures often provide unique and synergetic functionalities that are highly desirable in various practical applications. However, the fabrication of such systems with desired functionalities using cost-effective techniques is still a great challenge. In this work, we report a facile route for the preparation of novel Ag/SnO2 nano-obelisk arrayed thin films on silicon substrates by spray pyrolysis and thermal evaporation techniques. The prepared samples exhibited broadband antireflectance in both UV and visible regions attributed to the refractive index gradient and scattering provided by the nano-obelisk arrays. The localised surface plasmon resonance of silver nanocaps further enhanced the light absorption contributing to the antireflective property of the hybrid system. Ag/SnO2 nano-obelisk arrayed thin film exhibited excellent SERS performance with an enhancement factor of 1.13 × 108 with a limit of detection value of 10−12 M for the trace detection of R6G dye. In addition, Ag/SnO2 nano-obelisk arrayed thin film based SERS substrate exhibited good homogeneity across the measured spots and outstanding stability which are essential for quantitative field analysis. The results indicate that the Ag/SnO2 nano-obelisk arrayed thin films are efficient SERS substrates with the merits of having the ease of production, high sensitivity and stability for various practical sensing applications. [ABSTRACT FROM AUTHOR]

It is of great significance to construct specially designed gold nanocrystals (AuNCs) with precisely controllable size and morphology to achieve an excellent physicochemical performance. In this work, sea urchin-shaped AuNCs with tunable plasmonic property were successfully synthesized by the hybridized double-strand poly adenine (dsPolyA) DNA-directed self-assembly technique. Hybridized dsPolyA as the directing template had suitable rigidity and upright conformation, which benefited the controllable formation of these anisotropic multi-branched AuNCs with the assistance of surfactant. The effects of essential conditions influencing the synthesis and precise morphology control were investigated in detail. COMSOL simulation was used to evaluate their electromagnetic field distribution according to their morphologies, and the result suggested that sea urchin-shaped AuNCs had abundant 'hot spots' for surface-enhanced Raman scattering (SERS) detection due to their regular nanoprotuberance structure. Finally, sea urchin-shaped AuNCs with excellent SERS and catalytic performance were applied for the quantitative analysis of food colorant and catalytic degradation of potential pollutants. The SERS enhancement factor of sea urchin-shaped AuNCs was up to 5.27 × 106, and the catalytic degradation rate for 4-NP by these AuNCs was up to −0.13min−1. [ABSTRACT FROM AUTHOR]

We present a template-assisted fabrication method for a large-scale ordered arrays of ZnO nanorods (ZnO-NRs) modified with Ag nanoparticles (Ag-NPs), which possess high-density three-dimensional (3D) hot spots uniformly dispersed all over the substrate, being beneficial to ultrahigh sensitivity of surface enhanced Raman scattering (SERS) detection. These achieved Ag-NPs@ZnO-NRs arrays show high sensitivity, good spectral uniformity and reproducibility as substrates for SERS detection. Using the arrays, both dye molecules (rhodamine 6G, R6G) and organic pollutants like toxic pesticides (thiram and methyl parathion) are detected, with the detection limits of thiram and methyl parathion being 0.79 × 10−9 M and 1.51 × 10−8 M, respectively. In addition, the Ag-NPs@ZnO-NRs arrays have a self-cleaning function because the analyte molecules can be photocatalytic degraded using ultraviolet irradiation, showing that the 3D recyclable arrays have promising opportunities to be applied in rapid SERS-based detection of toxic organic pesticides. [ABSTRACT FROM AUTHOR]

In this paper, gold nanorods (GNRs) were synthesized and characterized by absorption spectroscopy, scanning electronic microscopy and dark-field scattering spectroscopy. The density of nanorods on the glass substrate has been controlled in order to select locations where a single particle can be illuminated by the excitation focal spot. Diarylethene photochromic molecules were deposited on the GNRs and surface enhanced Raman scattering experiments were performed in single particle condition to study both isomer’s forms. In addition, calculations were performed to precisely resolve each isomer’s vibrational modes. By combining both calculation and experiments, the open and closed forms of the photochromic molecule have been characterized. Moreover, the presence of conformers in the case of the open form has been pointed out, which is an important parameter to take into account of the photochromic process due to different photo-activity with respect to the antiparallel or parallel configuration. Thanks to the results obtained, we propose a method that could be used in further experiments to follow photochromic reactions based on the selection of a specific fingerprint, which allows us to unambiguously assign the detected signal to one isomer form of the photochromic molecule. [ABSTRACT FROM AUTHOR]

Combined surface enhanced Raman spectroscopy (SERS) and surface plasmon resonance (SPR) setup was proposed recently. The experimental setup requires a gold layer deposited on a glass substrate. However, due to the poor ability of sticking gold material on glass, a nanometric adhesion layer is used. In this paper we compare numerically both the SERS gain, and the SPR signal, for metallic and dielectric adhesion layers, for two substrates. We show that even if the dielectric materials can be considered as equivalent for the SPR signal, this is not the case for the SERS gain. In particular the dielectric adhesion layer reduces the sensitivity of the SERS gain to this parameter and therefore their use could be more suitable for the fabrication of the sensor. Moreover the higher the refractive index of substrate with regards to the adhesion layer is, the higher efficiency of setup is obtained, and therefore the Otto configuration seems to be more efficient than the Kretschmann one. Optimization of the thicknesses of the adhesion layer and of the gold layer can lead to a SERS gain greater than 103 without nanostructuring. [ABSTRACT FROM AUTHOR]

In this paper we report a triple-resonance surface-enhanced Raman scattering (SERS) chip that is able to provide simultaneous field enhancement for both the Stokes and anti-Stokes lines. The structure consists of an array of periodic gold bowties placed on the surface of a uniform gold film. It can support two localized surface plasmonic resonances (LSPRs): an electric dipole binding resonance (EDBR) and a magnetic dipole resonance (MDR). A third field enhancement peak is obtained by utilizing the strong interaction between the non-localized surface plasmonic resonance (non-localized SPR) and the LSPR, which greatly raises the field enhancement for the non-localized SPR. In addition, a gold strip-line resonator is incorporated to further enhance the local field intensity. Consequently, the field enhancement of the three peaks are all increased. Compared with the same structure without strip, the periodic bowtie-strip compound structure on gold film can gain as much as ∼22.8 times and ∼3.6 times larger Raman intensity enhancement simultaneously for both the Stokes and anti-Stokes lines. [ABSTRACT FROM AUTHOR]

Ag nanoparticles and nanostructured surfaces have been widely used as surface-enhanced Raman scattering (SERS) substrates, which can enhance the Raman signals when molecules are adsorbed on the surface of Ag by the effect of Ag-thiol bonds. In this paper, we propose an efficient method to remove the molecules adsorbed on Ag with sodium borohydride solution, providing a protocol to realize a reproducible and practicable Ag SERS substrate. A theoretical density function theory approach has been used to explain the mechanism of desorption. [ABSTRACT FROM AUTHOR]

Recent advances in nanotechnology and optics have paved the way for new plasmonic devices. One of them are nanopatch antennas that are simple and, at the same time, effective devices for localizing the electromagnetic field on a scale of less than 10 nm and can be used in photonic integrated circuits as effective sources of photons, including single-photon sources. In the present study, we investigate the radiative characteristics of a submonolayer of colloidal CdSe/CdS quantum dots that form island structures in a resonator: a cubic silver nanoparticle on an aluminum mirror. For detecting plasmonic nanoparticles on glass or metal surfaces, we propose a new technique involving a tunable laser and a confocal microscope. We provide a comparative study of the luminescence enhancement factors for QDs in the NPAs upon off-resonance excitation and at a wavelength close to the resonance; a significant difference in the luminescence enhancement factors (by order of magnitude) is demonstrated. A 60-fold reduction in the spontaneous emission time, as well as an increase in the radiation intensity by a factor of 330, has been obtained in the experiments. The increase in the spontaneous emission rate demonstrated for the quantum dots is explained by the Purcell effect. Full-wave simulations of electromagnetic fields were carried out for the model of the developed nanopatch antenna; luminescence enhancement factors and radiative efficiencies were calculated as well. [ABSTRACT FROM AUTHOR]

In this study, simultaneous measurement of surface plasmon resonance (SPR) and surface enhanced Raman scattering (SERS) on flat metallic surfaces was demonstrated in a setup based on the Kretschmann configuration at acoustic frequency. This asset facilitates matching the photon and the surface plasmon polaritons wavevectors by tunneling the photon in the total internal reflection geometry and we demonstrate the compensation for the absence of hotspots typical on rough surfaces. The optomechanical asset allows detecting the two signals and prevents their interference. Experimental and numerical analyses were done for characterizing the two signals. The results emphasize the enhancement of the electromagnetic field at the surface, which provides high sensitivity for detecting the signals coming from the Raman probe molecules such as Congo red and thiols such as cysteamine. The combination of simultaneous SPR–SERS microspectroscopy at low frequencies opens up interesting prospects that facilitate experimental conditions using standard SPR setups, with a dramatic reduction in sensor cost. [ABSTRACT FROM AUTHOR]

In this work, we propose a novel approach to design robust microfluidic devices with integrated plasmonic transducers allowing portability, reduced analysis time through dynamic measurements and high sensitivity. Specifically, the strategy we apply involves two steps: (i) the controlled deposition of gold bipyramidal nanoparticles (AuBPs) onto a functionalized solid glass substrate and (ii) the integration of the as-fabricated plasmonic substrate into a polydimethylsiloxane (PDMS) microfluidic circuit. The localized surface plasmon resonance (LSPR) sensitivity of the plasmonic-microfluidic device was evaluated by monitoring the optical responses at refractive index changes, proving a bulk sensitivity of 243 nm RIU−1 for the longitudinal LSPR band of isolated AuBPs and 150 nm RIU−1 for the band assigned to end-to-end linked nanoparticles. A strong electric field generated in the gaps between AuBPs—due to the generation of the so-called extrinsic 'hot-spots'—was subsequently proved by the volumetric surface enhanced Raman scattering (SERS) detection of molecules in continuous flow conditions by loading the analyte into the microfluidic channel via a syringe pump. In conclusion, our miniaturized portable microfluidic system aims to detect and identify, in real-time with high accuracy, analyte molecules in laminal flow, thus providing a groundwork for further complex biosensing applications. [ABSTRACT FROM AUTHOR]

In this paper, we describe the fabrication, simulation and characterization of dense arrays of freestanding silver capped polystyrene nanotubes, and demonstrate their suitability for surface enhanced Raman scattering (SERS) applications. Substrates are fabricated in a rapid, low-cost and scalable way by melt wetting of polystyrene (PS) in an anodized alumina (AAO) template, followed by silver evaporation. Scanning electron microscopy reveals that substrates are composed of a dense array of freestanding polystyrene nanotubes topped by silver nanocaps. SERS characterization of the substrates, employing a monolayer of 4-aminothiophenol (4-ABT) as a model molecule, exhibits an enhancement factor of ∼1.6 × 106, in agreement with 3D finite difference time domain simulations. Contact angle measurements of the substrates revealed super-hydrophobic properties, allowing pre-concentration of target analyte into a small volume. These super-hydrophobic properties of the samples are taken advantage of for sensitive detection of the organic pollutant crystal violet, with detection down to ∼400 ppt in a 2 μl aliquot demonstrated. [ABSTRACT FROM AUTHOR]

Human cardiac troponin I (cTnI) is a specific biomarker for diagnosis of acute myocardial infarction (AMI). In this paper, a composite sensing system of an optical microsphere resonator and silver nanoparticles based on surface enhanced Raman scattering (SERS) and stimulated Raman scattering (SRS) techniques towards a point of care diagnostic system for AMI using the cTnI biomarker in HEPES buffered solution (HBS) is proposed. Pump and Raman signals enter the optical fiber coupling into the microsphere, and then SRS occurs in the microsphere. The presence of silver nanoparticles on the microsphere surface provides a tremendous enhancement of the resulting Raman signal through an electromagnetic enhancement of both the laser excitation and Stokes-shifted light of the order of 1010. This enhancement occurs in metals as surface plasmon resonance (SPR), which increases the Raman gain through the SERS effect. Our simulation results show that this sensor presents a linear response for cTnI detection. The calculated enhanced Raman signal can be employed to detect the cTnI molecules around the microsphere. [ABSTRACT FROM AUTHOR]

Large-area ordered arrays with dense hotspots are highly desirable substrates for surface enhanced Raman scattering (SERS). In this paper, we present a quasi-3D SERS substrate of free-standing Ag triangle arrays (FATA) which was fabricated by nanosphere lithography incorporated with photolithography and Ag covering. A significant SERS effect arises from a strongly enhanced local electric field within the tiny gaps between the suspended Ag triangle and the Ag baseplate. The SERS intensity relative standard deviation is less than 7.6%, leading to excellent reliability for Raman detection. The simple fabrication of the Ag film covering FATA nanostructures provides a practical solution for large-area, highly efficient and reproducible SERS substrates. [ABSTRACT FROM AUTHOR]