High Surface Enhanced Raman Spectroscopy Research Articles

Cu/Ag Sphere Segment Void Array as Efficient Surface Enhanced Raman Spectroscopy Substrate for Detecting Individual Atmospheric Aerosol.

Surface enhanced Raman spectroscopy (SERS) shows great promise in studying individual atmospheric aerosol. However, the lack of efficient, stable, uniform, large-array, and low-cost SERS substrates constitutes a major roadblock. Herein, a new SERS substrate is proposed for detecting individual atmospheric aerosol particles. It is based on the sphere segment void (SSV) structure of copper and silver (Cu/Ag) alloy. The SSV structure is prepared by an electrodeposition method and presents a uniform distribution, over large 2 cm2 arrays and at low cost. The substrate offers a high SERS enhancement factor (due to Ag) combined with lasting stability (due to Cu). The SSV structure of the arrays generates a high density of SERS hotspots (1.3 × 1014/cm2), making it an excellent substrate for atmospheric aerosol detection. For stimulated sulfate aerosols, the Raman signal is greatly enhanced (>50 times), an order of magnitude more than previously reported substrates for the same purpose. For ambient particles, collected and studied on a heavy haze day, the enhanced Raman signal allows ready observation of morphology and identification of chemical components, such as nitrates and sulfates. This work provides an efficient strategy for developing SERS substrate for detecting individual atmospheric aerosol.

Multifunctional low temperature reduced graphite oxides for high performance supercapacitors and SERS applications

Graphene has been extensively investigated in the field of energy storage and optoelectronic applications due to its unique properties like high surface area, good electrical conductivity etc. Here, in the present work, we have synthesized few layer graphene via reduction of graphite oxide at low temperature (100 °C) using hydrazine hydrate and urea for energy storage. We studied the morphological changes occurred in prepared reduced graphite oxide (rGO) samples and activated to achieve better wettability for high capacitive performance and sustainability. The maximum specific capacitance of 300 Fg−1 was observed for activated electrode of rGO reduced with hydrazine hydrate (rGO-HH), while activated electrode of rGO reduced with urea (rGO-Urea) showed specific capacitance of 220 F g−1 at 1 Ag−1 discharge current in aqueous electrolyte. To the best of our knowledge, our rGO-HH shows higher capacitive performance and sustainability than other reports for the reduction process below 150 °C. Additionally, we have successfully demonstrated the suitability of prepared rGO samples as a substrate for surface enhanced Raman spectroscopy (SERS) to detect organic pollutant (Rhodamine 6G) at micro molar concentration for environmental remediation.

Recognition of plastic nanoparticles using a single gold nanopore fabricated at the tip of a glass nanopipette.

A single gold nanopore with high surface enhanced Raman spectroscopy (SERS) activity is fabricated on the tip of a glass nanopipette. Polystyrene (PS) nanospheres can be recognized from the SERS spectrum while passing through the single nanopore.

Graphene oxide wrapped with gold nanorods as a tag in a SERS based immunoassay for the hepatitis B surface antigen.

A composite consisting of graphene oxide and gold nanorods (GO-GNRs) was designed for the trace determination of hepatitis B surface antigen (HBsAg) using surface enhanced Raman spectroscopy (SERS). GO contains numerous carboxy and hydroxy groups on its surface and therefore can serve as the substrate for decoration with GNRs and for immobilizing antibody against HBsAg. The GNRs (carrying the SERS probe 2-mercaptopyridine) exhibit high SERS activity, and this improves the sensitivity of the biosensor. The antibody on the GO-GNRs binds HBsAg with high specificity, and it results in excellent selectivity. The SERS signal (measured at 1002cm-1) increases in the 1-1000pg·mL-1 HBsAg concentrations range, and the limit of detection is 0.05pg·mL-1 (at an S/N ratio of 3). The immunoassay achieves the sensitive and selective determination of HBsAg in serum and expands the potential application of GO-GNR based SERS tag in clinical research. Graphical abstract A novel graphene oxide-gold nanorod (GO-GNRs) based surface-enhanced Raman scattering (SERS) tag for immunoassay was designed. It allows for sensitive and selective determination of HBsAg in serum. The method is expected to expand the potential application in the environment, in medicine and in food analysis.

Substrate-Immersed Solvothermal Synthesis of Ordered SiO2/Ag Arrays as Catalytic SERS Substrates

In this work, we designed a simple substrate-immersed solvothermal route for the one-step synthesis of novel ordered SiO2/Ag arrays, employing SiO2 colloidal crystals as templates and alcohol as reducing agent. The Ag nanoparticles were uniformly deposited in situ onto SiO2 colloidal crystals, which exhibited high surface enhanced Raman spectroscopy (SERS) activity and uniform SERS intensity. It was found that ordered SiO2/Ag arrays could rapidly scavenge the absorbed-Nile blue A (NBA) molecules from the surfaces with the assistance of H2O2, while the SERS signals of NBA decreased sharply and almost completely disappeared within four minutes. This can be attributed to the superior catalytic activity of Ag nanoparticles. After five times of re-immersion and re-absorbing process of NBA, the substrates could still keep [Formula: see text] 74.8% SERS intensity versus the original. The high activity and durability of the as-prepared SiO2/Ag SERS substrate endow them as a promising candidate for trace detection.

Marangoni Convection Assisted Single Molecule Detection with Nanojet Surface Enhanced Raman Spectroscopy.

Many single-molecule (SM) label-free techniques such as scanning probe microscopies (SPM) and magnetic force spectroscopies (MFS) provide high resolution surface topography information, but lack chemical information. Typical surface enhanced Raman spectroscopy (SERS) systems provide chemical information on the analytes, but lack spatial resolution. In addition, a challenge in SERS sensors is to bring analytes into the so-called "hot spots" (locations where the enhancement of electromagnetic field amplitude is larger than 103). Previously described methods of fluid transport around hot spots like thermophoresis, thermodiffusion/Soret effect, and electrothermoplasmonic flow are either too weak or detrimental in bringing new molecules to hot spots. Herein, we combined the resonant plasmonic enhancement and photonic nanojet enhancemnet of local electric field on nonplanar SERS structures, to construct a stable, high-resolution, and below diffraction limit platform for single molecule label-free detection. In addition, we utilize Marangoni convection (mass transfer due to surface tension gradient) to bring new analytes into the hotspot. An enhancement factor of ∼3.6 × 1010 was obtained in the proposed system. Rhodamine-6G (R6G) detection of up to a concentration of 10-12 M, an improvement of two orders of magnitude, was achieved using the nanojet effect. The proposed system could provide a simple, high throughput SERS system for single molecule analysis at high spatial resolution.

An efficient sodium citrate-promoted synthetic method for the preparation of AuNPs@mesoSiO2 for surface enhanced Raman spectroscopy in the detection of diluted blood

We report on a novel, green, and efficient organically synthetic method for the preparation of gold nanoparticles embedded in mesoporous silica (AuNPs@mesoSiO2). AuNPs@mesoSiO2 prepared by one-pot synthesis method using sodium citrate as the key reactant was applied for surface enhanced Raman spectroscopy (SERS) application in the analysis of diluted blood traces. The synthesized nanoparticles are of high quality, as characterized by use of X-ray diffraction, scanning electron microscopy and transmission electron microscopy. They exhibit high surface areas (170.18–883m2/g) and significant SERS enhancement. Detection of diluted blood (v/v, 1:50) traces through AuNPs@mesoSiO2 enhanced SERS is demonstrated, which has not been studied in previous literature. The combination of the SERS and AuNPs@mesoSiO2 would be a valuable tool for forensic investigation.

Surface-enhanced Raman spectroscopy of blood serum based on gold nanoparticles for the diagnosis of the oral squamous cell carcinoma

BackgroundOral squamous cell carcinoma (OSCC) is becoming more common across the globe. The prognosis of OSCC is largely dependent on the early detection. But the routine oral cavity examination may delay the diagnosis because the early oral malignant lesions may be clinically indistinguishable from benign or inflammatory diseases. In this study, the new diagnostic method is developed by using the surface enhanced Raman spectroscopy (SERS) to detect the serum samples from the cancer patients.MethodThe blood serum samples were collected from the OSCC patients, MEC patients and the volunteers without OSCC or MEC. Gold nanoparticles(NPs) were then mixed in the serum samples to obtain the high quality SERS spectra. There were totally 135 spectra of OSCC, 90 spectra of mucoepidermoid carcinoma (MEC) and 145 spectra of normal control group, which were captured by SERS successfully. Compared with the normal control group, the Raman spectral differences exhibited in the spectra of OSCC and MEC groups, which were assigned to the nucleic acids, proteins and lipids. Based on these spectral differences and features, the algorithms of principal component analysis(PCA) and linear discriminant analysis (LDA) were employed to analyze and classify the Raman spectra of different groups.ResultsCompared with the normal groups, the major increased peaks in the OSCC and MEC groups were assigned to the molecular structures of the nucleic acids and proteins. And these different major peaks between the OSCC and MEC groups were assigned to the special molecular structures of the carotenoids and lipids. The PCA-LDA results demonstrated that OSCC could be discriminated successfully from the normal control groups with a sensitivity of 80.7% and a specificity of 84.1%. The process of the cross validation proved the results analyzed by PCA-LDA were reliable.ConclusionThe gold NPs were appropriate substances to capture the high-quality SERS spectra of the OSCC, MEC and normal serum samples. The results of this study confirm that SERS combined PCA-LDA had a giant capability to detect and diagnosis OSCC through the serum sample successfully.

Spherical silver nanoparticles as substrates in surface-enhanced Raman spectroscopy for enhanced characterization of ketoconazole

A new method was developed for the characterization and detection of ketoconazole using surface enhanced Raman spectroscopy (SERS) by designing substrates and performing the bands' assignments. Thus, spherical silver nanoparticles (Ag-NPs) were synthesized by a reduction method and designed as substrates for SERS application. The Ag-NPs were characterized using a scanning electron microscope, Fourier transformed infrared spectroscopy and a high-resolution transmission electron microscope. TEM results indicated that the average size of the Ag-NPs was 15nm. The UV spectrum showed a maximum absorbance of Ag-NPs at about 400nm. When Ag-NPs were used as substrates in SERS, the Raman spectra of KCZ showed a significant enhancement of the Raman bands. An important finding is a linear relationship between the logarithmical scale of KCZ concentration and the intensity of the SERS bands, for example at 1050cm−1 of KCZ, which is due to the CN vibration. This was optimized and utilized to develop a calibration curve, which was then used for the detection of the KCZ in real pharmaceutical samples. The method has the advantages of a wide dynamic range with a high coefficient of determination and detection limit calculated based on the signal-to-noise ratio of 3, was 2.6×10−10M and the limit of quantification was 7.8×10−10M. The potential applications that take advantage of the high SERS sensitivity of this method are discussed for practical KCZ analysis where were quantified with this method.

Observing Plasmon Damping Due to Adhesion Layers in Gold Nanostructures Using Electron Energy Loss Spectroscopy.

Gold plasmonic nanostructures with several different adhesion layers have been studied with monochromated electron energy loss spectroscopy in the scanning transmission electron microscope (STEM-EELS) and with surface enhanced Raman spectroscopy (SERS). Compared to samples with no adhesion layer, those with 2nm of Cr or Ti show broadened, lower intensity plasmon peaks as measured with EELS. This broadening is observed in both optically active ("bright") and inactive ("dark") plasmon modes. When the former are probed with SERS, the signal enhancement factor is lower for samples with Cr or Ti, another indication of reduced plasmon resonance. This work illustrates the capability of STEM-EELS to provide direct near-field measurement of changes in plasmon excitation probability with nano-scale spatial resolution. Additionally, it demonstrates that applications which require high SERS enhancement, such as biomarker detection and cancer diagnostics, can be improved by avoiding the use of a metallic adhesion layer.

High efficiency SERS detection of clinical microorganism by AgNPs-decorated filter membrane and pattern recognition techniques

A simple, low cost and rapid optical fingerprinting technology for clinical microorganism detection is demonstrated using silver nanoparticles (AgNPs)-decorated filter-like surface enhanced Raman spectroscopy (SERS) substrate combined with pattern recognition techniques. In this study, an easy silver-mirror reacted filter membrane produced notable intensity and more distinguishable peaks when compared with the spectra collected directly from an Au/Cr-coated substrate with regard to the detection of bacteria. For the recognition of complex spectra pattern, the data set structure was performed by preliminary study procedures as follows. First, data pre-treatment was processed by standard normal variant (SNV) and exploratory data analysis (EDA), variable selection and reduction. Second, pattern recognition technique including genetic algorithm (GA), k-nearest neighbour (k-NN) and partial least squares discriminant analysis (PLS-DA) were conducted. Third, the new processing algorithm was applied to three bacteria (Salmonella, Acinetobacter baumannii, Klebsiella pneumoniae) with great results. Finally, the uniqueness of the selected variable an iterative random subsample, leave-one-out cross-validation (LOOCV) procedure was further performed. The SERS fingerprint combination with pattern recognition techniques showed good classification of microorganism with respect to clinical rapid diagnostics. Prediction abilities of bacteria Raman and SERS spectra calculated through LOOCV can be achieve for 66% to 100%, respectively. This study represents a basic and low cost research tool that may allow researchers and medical doctors to rapidly detect, quantify, and classify bacterial type at species levels.

Ultrasensitive label-free detection of cardiac biomarker myoglobin based on surface-enhanced Raman spectroscopy

Acute myocardial infarction (AMI) is the leading cause of mortality worldwide. Myoglobin protein was used as a biomarker for AMI because of its higher sensitivity compared with other biomarkers. Its high sensitivity is attributed to its rapid release in the bloodstream. As such, many researchers have focused on developing label-free biosensors to detect myoglobin levels. This study developed a highly sensitive and label-free myoglobin sensor based on surface-enhanced Raman spectroscopy (SERS). The sensor consisted of new 3D silver anisotropic nano-pinetree array modified indium tin oxide (Ag NPT/ITO) substrates. Moreover, another three Ag nanostructure modified ITO substrates (nanoaggregates, nanorods and nanobranched) were developed to select the highest surface enhanced Raman spectroscopy. Results revealed that Ag NPT/ITO displayed the highest SERS performance compared with other substrates. This finding is attributed to the presence of numerous hotspots, particularly in the junctions between the central rod and side arms. The highly enhanced Raman effect of Ag NPT/ITO substrate was applied to develop an ultrasensitive biosensor for detecting myoglobin as a cardiac biomarker at low concentration levels in solutions (pH 7.4, phosphate buffer) and urine. This biosensor is potentially useful for real sample analysis. The 3D morphology of Ag NPT enhanced the sensitivity performance of the sensor and allowed myoglobin detection over a wide linear range with a detection limit of 10ng/mL.

Novel highly sensitive Cu‐based SERS platforms for biosensing applications

Novel surface enhanced Raman spectroscopy (SERS) platforms have been prepared and used for the bacteria detection. Unlike typical, expensive SERS platforms prepared from gold or silver, the presented platforms are prepared using copper. A new, simple, cost‐efficient and fast high pressure method is used for platform fabrication, through the decomposition of copper hydride. The platform enhancement factors are verified using the malachite green isothiocyanate as a standard. The platforms exhibit extremely high SERS enhancement factors depending on pressure used for their preparation. The calculated enhancement factors have been found in the range between 1.5 × 106 and 4.6 × 107. The SERS spectra reproducibility is established both across a single platform and among different platforms. The average spectral correlation coefficient (Γ) has been calculated to be 0.82. Fully characterized SERS platforms have then been used for detecting Staphylococcus aureus bacteria. These novel platforms have great potential to become excellent tools for biological or medical diagnostics as an alternative to more common silver or gold SERS platforms. Copyright © 2015 John Wiley & Sons, Ltd.

High sensitivity surface enhanced Raman spectroscopy of R6G on in situ fabricated Au nanoparticle/graphene plasmonic substrates

Plasmonic gold nanoparticles (AuNP) with controllable dimensions have been fabricated in situ on graphene at moderately elevated temperature for high sensitivity surface enhanced Raman spectroscopy (SERS) of Rhodamine 6G (R6G) dye molecules. Significantly enhanced Raman signature of R6G dyes were observed on AuNP/graphene substrates as compared to the case without graphene with an improvement factor of 400%, which is remarkably greater than previous results obtained in ex situ fabricated SERS substrate. Simulation of localized electromagnetic field around AuNPs with and without the underneath graphene layer reveals an enhanced local electromagnetic field due to the plasmonic effect of AuNPs, while additional Ohmic loss occurs when graphene is present. The enhanced local electromagnetic field by plasmonic AuNPs is unlikely the dominant factor contributing to the observed high SERS sensitivity on R6G/AuNP/graphene substrate. Instead, the p-doped graphene, which is supported by the large positive Dirac point shift away from “zero” observed in AuNP/graphene field effect transistors, promotes SERS signals through enhanced molecule adsorption and non-resonance molecular–substrate chemical interaction.

Study of faceted Au nanoparticle capped ZnO nanowires: antireflection, surface enhanced Raman spectroscopy and photoluminescence aspects

We report a single step growth process of faceted Au nanoparticles (NPs) on highly c-axis oriented ZnO nanowires (NWs) and report that a system with a lower antireflection coefficient also showed higher surface enhanced Raman spectroscopy (SERS) enhanced factors. Well-dispersed Au NPs are grown on silicon substrate using a thin film-in-air-annealing method (using 1 nm and 5 nm thick Au films on silicon and subsequent annealing in air at 800 °C) wherein enhanced oxide growth at the Au–Si interface was used to inhibit inter-diffusion to avoid Au–Si alloy formation (Au/SiOx/Si). These substrates are used to grow aligned ZnO NWs using a high temperature (≈900 °C) chemical vapour deposition method. Depending on the size and areal density of initial catalytic Au NPs, the resultant photoluminescence, reflectance characteristics, and effectiveness as SERS substrates of the faceted Au NP capped ZnO NWs coatings are systematically studied. The highly oriented and faceted Au NPs on ZnO NWs have been used as free standing SERS substrates to detect sub-micro molar crystal violet molecules with an analytical enhancement factor (AEF) of ≥104 and with high repeatability. The substrate with high-density Au–ZnO heterostructures (5 nm Au case) found to have larger AEF, very low reflectance (≈0.75%) and more green emission.

Synthesis of porous gold nanoparticle/MoS2 nanocomposites based on redox reactions

We develop a facile method for preparing the porous gold nanoparticles (Au-NPs)/2H-form MoS2 nanocomposite that forms a unique 3-dimensional structure and shows a high surface enhanced Raman spectroscopy effect.

Thermoresponsive PNIPAAm hydrogel scaffolds with encapsulated AuNPs show high analyte-trapping ability and tailored plasmonic properties for high sensing efficiency.

The fabrication of a scaffold able to control the positioning of AuNPs and to trap and concentrate target molecules inside them is a promising idea for a large variety of sensing applications. In this work, we designed and fabricated a scaffold of already-prepared 20 nm AuNPs encapsulated in a PNIPAAm hydrogel and utilizing surface enhanced Raman spectroscopy (SERS), we used it as a sensor with remarkably low limits of detection. In fact, as the target is trapped inside the hydrogel, the following takes place: (a) the concentration of the target increases dramatically and (b) the localization of the AuNPs and thus of the hotspots (areas with extremely high SERS enhancement factors) work synergistically, improving the sensing ability of the scaffold. The SERS enhancement ability of our scaffolds was checked with adenine, 2-naphthalenethiol and melamine molecules; the trapping efficiency was investigated for the melamine and a partition coefficient of k = 5 × 105 was found. Finally, by focusing on a single PNIPAAm hydrogel with encapsulated AuNPs, we managed to detect 10-6 M or rather 108 molecules of melamine trapped inside the scaffold.

STEM Tomography and Surface Plasmon Imaging of a Au-Pd Bi-metallic Nanorod with Exotic Morphology

Utilizing surface enhanced Raman spectroscopy (SERS) to in situ monitor a catalytic reaction requires a bi-functional platform which is both catalytically and plasmonically active. In this study, we developed a novel bimetallic nanostructure, featuring Au-Pd alloy horns selectively grown on the end of Au nanorods (AuNR@AuPd), and employed electron tomography and electron energy loss spectroscopy (EELS) to visualize its 3-D morphology as well as the distribution of its surface plasmon. The results well explain the observed high catalytic activity and SERS sensitivity of this new material [1].

Highly Sensitive Surface Enhanced Raman Spectroscopy from Ag Nanoparticles Decorated Graphene Sheet

Surface enhanced Raman spectroscopy (SERS) is a powerful analytical technique and has been most intensively studied. In this work, electroless deposition is proposed for Ag nanoparticles (NPs) decorated on chemical vapor deposition (CVD) growth graphene sheets (GS) to create hybrid SERS substrate. From three aspects of size distribution, morphology, and coverage, Ag NPs controllable decoration on GS and SERS enhancement factors of the hybrid SERS substrate is investigated. 200–300 times enhanced SERS intensities are detected from the Ag NPs on GS hybrid as compared to pure GS. Controllable decoration is crucial for improving SERS enhancement factors βEF, because βEF from quasi cubic Ag NPs on GS is 6.53 times stronger than that from spheric one; 1.6 times βEF is detected while the Ag NPs size distribution is reduced to half, and when the coverage is doubled, βEF is nearly doubled. This controllable Ag NPs/GS hybrid is capable of serving as a high performance SERS substrate for efficient chemical and biological sensing applications.

Preparation of highly water dispersible functional graphene/silver nanocomposite for the detection of melamine

A stable aqueous suspension of a functional graphene/silver (FG/Ag) nanocomposite was prepared by an environmentally friendly hydrothermal method. The precursor, functional graphene oxide (FGO), was prepared by covalent functionalisation of graphene oxide (GO) with a hydrophilic organosilane, N-(trimethoxysilylpropyl) ethylenediaminetriacetic acid trisodium salt (TETA). The attachment of functional groups on the GO surface maintained the aqueous stability of the FG/Ag nanocomposite even after the hydrothermal reduction. Field emission scanning electron microscopy (FESEM) images illustrated a uniform distribution of Ag nanoparticles on the FG surface. The surface enhanced Raman spectroscopy (SERS) activity of the nanocomposite was investigated using p-aminothiophenol (p-ATP) and melamine which can be detected as low as 2×10−8 and 2×10−7M, respectively. The impressive water stability and the high SERS sensitivity of the FG/Ag nanocomposite make it a suitable substrate for trace analysis of a variety of drugs, additives or organic contaminants in water. The nanocomposite also showed a positive inhibition effect against the growth of Escherichia coli bacteria, eliminating the possibility of bacterial contamination of the sensor, thus prolonging the shelf-life of the sensing device.