Synthesis of ultrathin and compact Au@MnO2 nanoparticles for shell‐isolated nanoparticle‐enhanced Raman spectroscopy (SHINERS)

Shell‐isolated nanoparticle‐enhanced Raman spectroscopy (SHINERS) based on Au@SiO₂ or Au@Al₂O₃ nanoparticles (NPs) shows great potential to break the long‐standing limitations of substrate and surface generality of surface‐enhanced Raman scattering (SERS). However, the shell of SiO₂ or Al₂O₃ can easily be dissolved in alkaline media, which limits the applications of SHINERS in alkaline systems. Besides that, the synthesis of Au@SiO₂ NPs can be further simplified and Au@Al₂O₃ NPs be replaced by other NPs that are more amenable for mass production. In an attempt to make SHINERS NPs available in any systems practically, we report the synthesis of ultrathin and compact Au@MnO₂ NPs. The shell thickness of MnO₂ can be controlled down to about 1.2 nm without any pinhole. SHINERS based on such Au@MnO₂ NPs exhibits much higher Raman enhancement effect than Au@SiO₂ NPs and can be applied in alkaline systems in which Au@SiO₂ or Au@Al₂O₃ NPs cannot be applied. Copyright © 2011 John Wiley & Sons, Ltd.     

Simple and sensitive detection of cyanide using pinhole shell‐isolated nanoparticle‐enhanced Raman spectroscopy

Cyanide is a great threat to public health, environmental safety and homeland security because of its extremely high toxicity and widespread usage in industry. Countering such a threat can be greatly aided by a rapid, sensitive, on‐site detection method. Here, a pinhole shell‐isolated nanoparticle‐enhanced Raman spectroscopy (SHINERS) technique for cyanide sensing has been established, and a limit of detection lower to 1 µg l⁻¹ level in water was achieved on a portable Raman spectrometer, owing to the magnificent local electromagnetic field enhancement generated by the interaction between cyanide anion and the uncovered Au surface inside the pinholes. Meanwhile, the silica shell outside the Au core could significantly improve the stability of the substrate by preventing the dissolution of Au in cyanide solution, thereby making this assay more feasible for practical use. The linear range was from 1 to 100 µg l⁻¹ with excellent selectivity over thiocyanide and other common ions. For applications on complex matrices such as polluted water, beverages etc., a simple online hydrogen generator was designed and successfully coupled with pinhole SHINERS to achieve a good measurement of cyanide. This pinhole SHINERS‐based method is rapid, simple, with good stability and feasibility for the in‐field detection of cyanide, and we hope that it will further raise more opportunities for portable SERS applications. Copyright © 2014 John Wiley & Sons, Ltd.     

Shell‐isolated nanoparticle enhanced Raman spectroscopy (SHINERS) investigation of benzotriazole film formation on Cu(100), Cu(111), and Cu(poly)

Benzotriazole (BTAH) is well known as an effective corrosion inhibitor for Cu because of its ability to make a coordination polymer film on the surface that provides a barrier to Cu oxidation. BTA⁻ film formation was investigated on single‐crystal and polycrystalline Cu surfaces with shell‐isolated nanoparticle enhanced Raman spectroscopy (SHINERS) using silica‐encapsulated Au nanoparticles. Potential‐dependent spectra display reversible film formation on polycrystalline Cu and irreversible film formation on single‐crystal Cu. Grain boundaries leading to smaller BTA⁻‐Cu oligomers are proposed to be the reason for cathodic degradation of the BTA⁻ polymeric films on polycrystalline Cu. Copyright © 2011 John Wiley & Sons, Ltd.     

Au@SiO2 core/shell nanoparticle assemblage used for highly sensitive SERS‐based determination of glucose and uric acid

The use of Au@SiO₂ core/shell nanoparticle (NP) assemblage with highly sensitive surface‐enhanced Raman scattering (SERS) was investigated for the determination of glucose and uric acid in this study. Rhodamine 6G dye molecules were used to evaluate the SERS enhancement factor for the synthesized Au@SiO₂ core/shell NPs with various silica shell thicknesses. The enhancement of SERS signal from Rhodamine 6G was found to increase with a decrease in the shell thickness. The core/shell assemblage with silica layer of 1–2 nm over a Au NP of ~36 nm showed the highest SERS signal. Our results show that the SERS technique is able to detect glucose and uric acid within wide concentration ranges, i.e. 20 ng/dL to 20 mg/dL (10⁻¹²–10⁻³ M) and 16.8 ng/dL to 2.9 mg/dL (10⁻¹¹–1.72 × 10⁻⁴ M), respectively, with associated lower detection limits of ~20 ng/dL (~1.0 × 10⁻¹² M) and ~16.8 ng/dL (~1.0 × 10⁻¹¹ M). Our work offers a low‐cost route to the fabrication of agile sensing devices applicable to the monitoring of disease progression. Copyright © 2013 John Wiley & Sons, Ltd.     

A novel approach to determine leucomalachite green and malachite green in fish fillets with surface‐enhanced Raman spectroscopy (SERS) and multivariate analyses

The use of illegal fish drugs, such as malachite green (MG) in aquaculture has raised growing concerns over the safety of aquatic food products, and sensitive and rapid methods for detection of these drugs in fish muscle are much needed. Simplified extraction methods coupled with surface‐enhanced Raman spectroscopy were used for analysis of MG and its metabolite leucomalachite green (LMG) in tilapia fillets containing 0–50 ng g⁻¹ LMG or MG. Principal component analysis and partial least squares (PLS) regression were used for spectral data analyses. High sensitivity (MG or LMG could be detected at 1–2 ng g⁻¹ levels) and PLS models with good predictability [root mean square error of validation (RMSEV) = 1.97–2.21 ng g⁻¹, R² = 0.984–0.988] were possible with suitable sample extraction methods. The simplest extraction method developed provided an RMSEV of 9.32 ng g⁻¹ and R² of 0.788, and although this was not ideal, detection of MG and LMG at 5 ng g⁻¹ level with this method could reduce sample throughput time and provide for faster detection of LMG and MG. Copyright © 2012 John Wiley & Sons, Ltd.     

Large scale synthesis of pinhole‐free shell‐isolated nanoparticles (SHINs) using improved atomic layer deposition (ALD) method for practical applications

Shell‐isolated nanoparticle‐enhanced Raman spectroscopy (SHINERS) as a new member of Raman technique garnered great attention among scientific community. In this work, we used an improved experimental setup to float the bare silver nanoparticles in air with the help of extraneous airflow, and used atomic layer deposition (ALD) method to coat ultra‐thin inert shell without pinholes. Under optimal conditions, we successfully prepared three kinds of SHINERS NPs (Ag@Al₂O₃, Ag@SiO₂ and Ag@TiO₂) in large quantity without pinholes. The ultra‐thin inert shell maintains the SERS activity of silver nanoparticles for long period of time. Transmission electron microscopy (TEM) images confirm the uniform coating of shell material on silver nanoparticles. Finally, the as‐prepared SHINs have been applied to detect various samples to demonstrate the applications. The presented ALD method offers a unique way to coat ultrathin shell (1–10 nm) on metal nanoparticles in large quantity (1–10 g) for practical applications. Copyright © 2015 John Wiley & Sons, Ltd.     

Thickness‐dependent electroforming behavior of ultra‐thin Ta2O5 resistance switching layer

Electroforming behaviours of Ta₂O₅ resistance switching memory cell with a diameter of 28 nm and different thickness (0.5–2.0 nm) of Ta₂O₅ layer have been examined. The devices showed a constant forming electric field of 0.54 V/nm regardless of Ta₂O₅ thickness. The electroforming with negative bias to top TiN electrode was ascribed to electric field‐ driven migration of oxygen vacancies, originally residing near the bottom interface, toward the top electrode interface and formation of conducting filaments. The estimated electroforming energy (0.094–0.14 eV) was favourably compared with the hopping energy of electrons from the V_O site to a nearby Ta site. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Rapid atto‐molar level detection of surface‐enhanced Raman spectroscopy technique based on glycidyl methacrylate–ethylene dimethacrylate (GMA–EDMA) porous material

A novel miniature device for rapid ultra‐sensitive surface‐enhanced Raman scattering (SERS) detection was developed in the present study. The device was made of a syringe, a piece of filter, and a Teflon tube. Therefore, it was with advantages of simplicity, miniaturization, and easy operability. The tube was filled in advance with the glycidyl methacrylate‐ethylene dimethacrylate powder porous material which has been proved to increase the sensitivity of normal SERS dramatically, then the mixture solution containing the analyte, silver colloid, and NaCl solution passed through the porous material by the action of the syringe. SERS signals were collected from the surface of the material. Rhodamine 6G (R6G), p‐aminothiophenol (PATP), and thiabendazole (TBZ) were employed as the probe molecules in the present work. R6G at microlitre‐scale can be detected at an extremely low concentration of 10^–18 mol/l, and the relative standard deviation of spot to spot is 14.16% at the intensity of the band at 609 cm⁻¹. The concentrations of PATP and TBZ that can be detected with the method are 10⁻¹¹ mol/l and 1.3 × 10⁻⁶ mol/l, respectively. This method not only has achieved the ultra‐sensitive detection of dye and pesticide but also realized the simple, rapid, and small sample quantity requirement detection, and it is of great potential use for lots of analytes. Copyright © 2013 John Wiley & Sons, Ltd.     

Design of plasmonic bowtie nanoring array with high sensitivity and reproducibility for surface‐enhanced Raman scattering spectroscopy

A metallic bowtie nanoring array is designed to gain high sensitive and reproducible substrate for surface‐enhanced Raman scattering (SERS) spectroscopy. The localized surface plasmon resonance (LSPR), the electric field enhancement factors (EFs) and the electric field distribution of the bowtie and bowtie nanoring array are numerically investigated by means of the finite‐difference time domain (FDTD) method. After the optimization of the particle size and the array period, the maximum electromagnetic field EF approaches 153, and the corresponding SERS electromagnetic enhancement factor (EMEF) reaches 5.4 × 10⁸. This highly sensitive and reproducible substrate can be a good candidate for SERS applications. Copyright © 2011 John Wiley & Sons, Ltd.     

Surface‐enhanced Raman spectroscopy (SERS) on silver colloids for the identification of ancient textile dyes: Tyrian purple and madder

Surface‐enhanced Raman spectroscopy (SERS) was used for the identification of natural organic dyes belonging to indigoid and anthraquinone classes in archeological samples, and good agreement with the corresponding reference commercial materials was found. Special attention was paid to the well‐known problem of anomalous bands that arise sometimes in the SERS spectra on colloids: as suggested in the literature, this problem could be reduced by the use of poly‐L ‐lysine and ascorbic acid as aggregating agents, but we observed that also the addition first of the analyte and subsequently of suitable electrolytes to the colloid in an inverted order compared to the most widely used method can be of help in limiting the intensity of such spurious bands. This procedure allowed us to obtain, for the first time, the SERS spectra of both modern and ancient Tyrian purple and to solve a specific problem observed in the analysis of archeological wool samples dyed with madder lake, i.e. the competition in the SERS response between the dye and other compounds possibly deriving from the degradation of the peptide chain during the hydrolysis treatment during the extraction of the dye from the wool fiber. Copyright © 2009 John Wiley & Sons, Ltd.     

Chromatographic paper embedded with silver nanostructure as a disposable substrate for surface‐enhanced Raman spectroscopy and catalytic reactor

The high cost of regular diagnostic kits severely impeded its uses for routine clinical assay and fieldworks. A cost‐effective chromatography paper is chemically modified with Ag nanostructures using the simple electroless silver deposition, producing a scalable and disposable substrate for surface‐enhanced Raman spectroscopy, as well as a large scale of catalytic active sites over many chemical reactions. Synergetic measurement including surface‐enhanced Raman spectroscopy and laser desorption ionization‐mass spectrometry is performed on Ag decorated filter paper using a thiol containing compound as indicator, allowing for the acquisition of spatially correlated spectroscopy in the tandem mode. In addition, hydrophilic porous cellulose network that contains a certain amount of liquid naturally served as a chemical reactor for molecular transport and reaction. Positive results from catalytic reaction on metallized paper convincingly demonstrated that total microanalysis system on paper (μ‐TASoP), as a compelling alternative would find a wide breadth of applications in developing disposable medical devices and customary laboratory assays. Copyright © 2015 John Wiley & Sons, Ltd.     

Effects of trap density on the surface‐enhanced Raman scattering of molecules adsorbed on TiO2 (Degussa P25)

The surface‐enhanced Raman scattering (SERS) of molecules on TiO₂ (Degussa P25) was investigated. The variation of trap density was carried out by the calcination of TiO₂ at 350, 450 and 600°C. We found that the SERS intensity increases first, and then decreases with the calcination temperature rising from 350 to 450°C and 450 to 600°C, respectively. The measurements indicate that the trap density increases with the calcination temperature rising. The results indicate that the increase of trap density is favorable for the increase of SERS enhancement. The increase of SERS intensity from 350 to 450°C could be due to the dominated contribution from the trap density increase, and the decrease from 450 to 600°C could be due to dominated contribution from the increase of the crystallite size and the mass fraction of rutile phase. Copyright © 2012 John Wiley & Sons, Ltd.     

Surface‐enhanced Raman scattering (SERS) and complementary techniques applied for the investigation of an Italian cultural heritage canvas

A cultural heritage canvas from the early 19^th century, painted by the Vaccaro brothers for the church of Niscemi, province of Caltanissetta, Sicily, was analyzed using Fourier transform (FT)‐Raman, attenuated total reflectance‐FT‐infrared and surface enhanced Raman scattering (SERS) spectroscopy. The painting, still used in religious rites related to the Easter mass (‘la calata da tila’), depicts the scene of the Crucifixion and is executed in a scarce palette, with white, green and blue colors. Analysing vibrational data in conjunction with scanning electron microscopy and solid ‐state ¹³C‐NMR signals of the linen threads, we were able to offer valuable insight into the painting technique, unknown prior to this study. SERS is usually employed in artwork diagnosis for the identification of organic lakes and dyes. Due to its sensitivity, SERS has been successfully applied for the detection of either organic painting materials (indigo) that are usually not resolved by conventional Raman spectroscopy or of inorganic pigments difficult to observe in the presence of highly fluorescent aged organic supports or binders. To the best of our knowledge, this is also the first report on the SERS investigation of flax used in linen from cultural heritage objects using Ag colloidal nanoparticles. Copyright © 2012 John Wiley & Sons, Ltd.     

Using surface‐enhanced Raman scattering (SERS) and fluorescence spectroscopy for screening yeast extracts,a complex component of cell culture media

Yeastolate or yeast extract, which are hydrolysates produced by autolysis of yeast, are often employed as a raw material in the media used for industrial mammalian cell culture. The source and quality of yeastolate can significantly affect cell growth and production; however, analysis of these complex biologically derived materials is not straightforward. The best current method, liquid chromatography–mass spectrometry (LC‐MS), is time‐consuming and requires extensive expertise. This study describes the use of surface‐enhanced Raman scattering (SERS) and fluorescence excitation–emission matrix (EEM) spectroscopy coupled with robust principal component analysis (ROBPCA) for the rapid and facile characterization and discrimination of yeast extracts in aqueous solution. SERS using silver colloids generates time‐dependent signals, where adenine is the strongest contributor, and the spectra are stable and reproducible (< ~3%) at 180 min after mixing. Combining this spectral behavior with chemometric methods enables SERS to be used in discriminating between different yeastolate sources, for assessing lot‐to‐lot variability, and, potentially, to monitor storage‐induced compositional changes. Fluorescence EEM combined with multiway ROBPCA also provides a rapid and inexpensive method for the discrimination of yeastolate, yielding results in terms of sample discrimination very similar to that obtained with SERS. However, the EEM data does not provide the same level of chemical information that is provided by the SERS. Thus, the combination of these two methodologies has the potential to be extremely useful in biopharmaceutical manufacturing, as well as for the rapid characterization and screening of biogenic hydrolysates from animal or plant sources. Copyright © 2011 John Wiley & Sons, Ltd.     

Pressure-induced line broadening for the (30012)←(00001) band of CO2 measured with tunable diode laser photoacoustic spectroscopy

Pressure-induced foreign-broadening lineshape parameters of the carbon dioxide rovibrational transitions belonging to the (30012)←(00001) overtone band near the 1.573 μm wavelength region are measured by using a tunable diode laser photoacoustic spectrometer. The spectroscopic analysis has concerned the first 11 lines of the R branch. For these lines, the air- and Ar-broadening coefficients are measured at room temperature (∼298 K). The measured broadening coefficients of all the transitions of ¹²C¹⁶O₂ are compared with those given in the HITRAN04 database and former measurements with a different spectroscopic method. Agreements and discrepancies are underlined and briefly discussed. The recorded lineshapes are fitted with standard Voigt line profiles in order to determine the collisional broadening coefficient of carbon dioxide transitions.     

Surface‐enhanced Raman spectroscopy (SERS) on silver colloids for the identification of ancient textile dyes. Part II: pomegranate and sumac

The effectiveness of surface‐enhanced Raman spectroscopy (SERS) spectrocsopy on Ag colloids has been successfully demonstrated for the identification of a yellow dye in two ancient wool threads found in the Royal Tumulus of In Aghelachem, Libyan Sahara, belonging to the Garamantian period (2nd–3rd century A.D.). High‐performance liquid chromatography (HPLC) highlighted the presence of ellagic acid in the extracts from the threads, excluding other chromophores. This result, together with the abundance of malic acid detected by gas chromatography‐mass spectrometry (GC‐MS), suggested the possible use of pomegranate rind or sumac berries as source of the yellow dye, both plants being documented in the Fezzan area during the Garamantian period. HPLC analyses and SERS spectra acquired on the extracts of the ancient threads were therefore compared with those obtained from pomegranate and sumac extracts of the corresponding fruits and reference dyed wool samples, allowing us to identify the yellow dye as deriving from pomegranate (Punica granatum L.). SERS spectra of ellagic acid and dyes extracted from pomegranate rind and sumac berries are reported here for the first time. A methodological improvement is also presented, based on the use of NaClO₄ as aggregating agent, that leads to a significant increase of the signal‐to‐noise ratio in the SERS spectra. Copyright © 2010 John Wiley & Sons, Ltd.     

Raman spectroscopic study of the hydrogen‐arsenate mineral pharmacolite Ca(AsO3OH)·2H2O—implications for aquifer and sediment remediation

The removal of arsenate anions from aqueous media, sediments and wasted soils is of environmental significance. The reaction of gypsum with the arsenate anion results in pharmacolite mineral formation, together with related minerals. Raman and infrared (IR) spectroscopy have been used to study the mineral pharmacolite Ca(AsO₃OH)· 2H₂O. The mineral is characterised by an intense Raman band at 865 cm⁻¹ assigned to the ν₁ (AsO₃)²⁻ symmetric stretching mode. The equivalent IR band is found at 864 cm⁻¹. The low‐intensity Raman bands in the range from 844 to 886 cm⁻¹ provide evidence for ν₃ (AsO₃) antisymmetric stretching vibrations. A series of overlapping bands in the 300‐450 cm⁻¹ region are attributed to ν₂ and ν₄ (AsO₃) bending modes. Prominent Raman bands at around 3187 cm⁻¹ are assigned to the OH stretching vibrations of hydrogen‐bonded water molecules and the two sharp bands at 3425 and 3526 cm⁻¹ to the OH stretching vibrations of only weakly hydrogen‐bonded hydroxyls in (AsO₃OH)²⁻ units. Copyright © 2009 John Wiley & Sons, Ltd.     

Temperature dependence of anisotropic displacement parameters in O3‐type NaM O2 (M = Cr and Fe): Comparison with isostructural LiCoO2

O3‐type NaM O₂ (M = Cr and Fe) is a promising cathode material for sodium ion secondary batteries (SIBs). Here, we investigate the temperature dependence of anisotropic displacement parameters, U₃₃ and U₁₁, in NaM O₂ by synchrotron radiation X‐ray powder diffraction measurements. In both compounds, the displacement ratios $(r \equiv \sqrt {U_{33} /U_{11} } - 1)$ for M and O are positive, reflecting the out‐of‐plane thermal displacement of the M O₂ layer. On the other hand, the r value for Na is negative, reflecting the two‐dimensional (2D) host structure. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Real‐time analysis of the microstructural evolution and optical properties of Cu(In,Ga)Se2 thin films as a function of Cu content

Thin films of Cu(In,Ga)Se₂ with various copper contents were deposited by co‐evaporation onto thermally oxidized silicon substrates. Characterization by real‐time spectroscopic ellipsometry reveals clear similarities among the samples, as well as key variations with Cu content. Although all films exhibit a Volmer–Weber nucleation and similar fundamental critical point energies in the analysis of optical properties, Cu‐rich films exhibit enhanced coalescence, smoother surfaces, larger grain sizes, as well as a sub‐bandgap absorption which is absent in Cu‐poor films. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)