In situ nucleation and growth of silver nanoparticles in membrane materials: a controllable roughened SERS substrate with high reproducibility

A controllable roughened silver surface with high surface‐enhanced Raman scattering (SERS) activity and high reproducibility has been developed in this study. This silver surface was prepared by silver nucleation in polyelectrolyte multilayers (PEMs) and silver‐enlarged growth. First, the small Ag nuclei were synthesized by NaBH₄ in situ reduction of Ag ions on a surface of PEMs. Then the small Ag nuclei formed were effectively enlarged by using a mixture of commercially available reagents named Li Silver . The optical properties and morphologies of the silver substrates have been investigated by ultraviolet–visible (UV–vis) spectroscopy and atomic force microscopy (AFM). The UV–vis and AFM results revealed that the small Ag nuclei separately appeared on the PEMs after NaBH₄ in situ reduction. The size of the enlarged Ag nanoparticles can be easily controlled with the immersing cycle in Li Silver. 4‐Mercaptopyridine (4‐MPY) and Rhodamine 6G (R6G) have been used as Raman probes to evaluate the properties of the new SERS substrates. It has been found that the enhancement factor of R6G reached ∼10⁹ after treatment in Li Silver. Reproducibility has been investigated using the SERS signal intensity at 1094 cm⁻¹ of 4‐MPY. Signals collected over multiple spots within the same substrate resulted in a relative standard deviation (RSD) of 6.38%, while an RSD of 10.33% was measured in signals collected from different substrates. Copyright © 2008 John Wiley & Sons, Ltd.     

Poly(vinylpyrrolidone)‐stabilized silver nanoparticles for strained‐silicon surface enhanced Raman spectroscopy

Poly(vinylpyrrolidone)‐stabilized silver nanoparticles deposited onto strained‐silicon layers grown on graded Si_1−xGe_x virtual substrates are utilized for selective amplification of the Si–Si vibration mode of strained silicon via surface‐enhanced Raman scattering spectroscopy. This solution‐based technique allows rapid, highly sensitive and accurate characterization of strained silicon whose Raman signal would usually be overshadowed by the underlying bulk SiGe Raman spectra. The analysis was performed on strained silicon samples of thickness 9, 17.5 and 42 nm using a 488 nm Ar⁺ micro‐Raman excitation source. The quantitative determination of strained‐silicon enhancement factors was also made. Copyright © 2011 John Wiley & Sons, Ltd.     

SER(R)S of porphyrins on Ag nanoparticles immobilized by silane: a unique way to obtain free‐base porphyrin spectra

We measured the surface‐enhanced resonance Raman scattering (SER(R)S) spectra of 5,10,15,20‐tetrakis (1‐methyl‐4‐pyridyl)porphyrin (TMPyP) by using solid SERS‐active substrates: Ag nanoparticles immobilized by aminosilane on glass plates. We report the surprising result that by using such substrates it is possible to obtain SER(R)S spectra of porphyrins in the unperturbed free‐base form, although by using silver nanoparticles directly in solution, the porphyrin molecules are completely metalated. We suggest that silane used for nanoparticle immobilization modifies the surface properties and, therefore, makes porphyrin metalation impossible. Copyright © 2007 John Wiley & Sons, Ltd.     

Development of a sensitive,stable and EGFR‐specific molecular imaging agent for surface enhanced Raman spectroscopy

We created and studied a novel nanoprobe for spectroscopic molecular imaging of the epidermal growth factor (EGF) receptor, whose over‐expression is a hallmark of a wide range of cancers. Silver nanoparticles (AgNPs) of 45 nm diameter were synthesized and coupled to EGF by α‐lipoic acid, a short ligand that exhibits excellent silver binding affinity. Time‐of‐flight mass spectroscopy demonstrates formation of the protein complex. Enzyme‐linked immunosorbent assay verifies the protein complex is 100% active for the EGF receptor, alone and, following conjugation to silver nanoparticles. Compared with its monosulfide analog, 6‐mercaptohexanoic acid, α‐lipoic acid is stabilized by binding to silver with a total energy that is lower by 1.38 eV, as found from Density Functional Theory (DFT)/natural bond analysis calculations. A Highest Occupied Molecular Orbital (HOMO)‐Lowest Unoccupied Molecular Orbital (LUMO) gap energy of 5.25 (spin‐up electrons) and 5.74 eV (spin‐down electrons) was obtained for the silver‐α‐lipoic acid complex. This is the first report of silver nanoparticles being attached to EGF, and the first theoretical and experimental report on the surface enhanced Raman spectroscopy spectral interpretation of α‐lipoic acid bound to silver. These nanoprobes exhibit surface enhanced Raman spectroscopy, when aggregated in solution, at picomolar concentrations and have the necessary properties – specificity, sensitivity and stability – to serve as molecular imaging agents. Copyright © 2015 John Wiley & Sons, Ltd.     

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.     

Adsorptive parameters and influence of hot geometries on the SER(R) S spectra of methylene blue molecules adsorbed on gold nanocolloidal particles

The vibrational signatures of methylene blue (MB) dye molecule have been reported. Complete vibrational assignments of the molecule are presented for the first time. Concentration‐dependent surface enhanced resonance Raman scattering [SER(R) S] spectra of the molecule have been investigated. Fluorescence spectroscopic technique has been applied to explore the concentration of the probe molecule actually adsorbed on the gold nanocolloidal (AuNC) surface. The free energy of adsorption and saturated concentration of MB molecules on AuNC surface are also estimated. Gigantic enhancements ~10⁵–10¹³ orders of magnitude have been recorded for the enhanced Raman bands in the SER(R) S spectra. The possible orientation of the molecule on the AuNC surface and their probable protrusions within the hot spots have been suggested. The hot geometries and correlation between the plasmonic behavior of the nanoparticles and enhancement efficiencies of the SER(R) S band have been mapped with the aid of three‐dimensional finite difference time domain (3D‐FDTD) simulations. Application of soft lithographic technique to engineer the pattern formation of hetero dimeric spherical aggregates will be an interesting field of study in future to enhance the detection limit of this and similar types of dye molecules. Copyright © 2015 John Wiley & Sons, Ltd.     

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.     

滤纸SERS基底的制备及其在精浆分析中的应用

本文介绍浸泡法制备基于滤纸的SERS基底,并分析滤纸SERS基底表面银纳米粒子(AgNP)的分布与浸泡时间的关系。以精浆为检测对象,相比于514nm波长激发,785nm激发可获得更好的光谱数据,同时还比较了该波长激发下精浆的常规拉曼光谱与SERS光谱。更为重要的是,通过采用精浆中654cm-1谱峰强度评估不同浸泡时间下(6h,12h,24h)滤纸SERS基底的增强性能和测量结果的重复性。实验结果表明,12h浸泡获得的滤纸SERS基底表面具有均匀的AgNP分布,在785nm波长激发下,纸基SERS基底可提供增强效果及光谱重复性俱佳的精浆SERS光谱。     

Preparation and characterisation of crystalline tris(acetylacetonato)Fe(III) films grown on p-Si substrate for dielectric applications

Thin tris(acetylacetonato)iron(III) films were prepared by sublimation in vacuum on glass and p-Si substrates. Then comprehensive studies of X-ray fluorescence (XRF), X-ray diffraction (XRD), optical absorption spectroscopy, AC-conductivity, and dielectric permittivity as a function of frequency and temperature have been performed. The prepared films show a polycrystalline of orthorhombic structure. The optical absorption spectrum of the film was identical with that of the bulk powder layer. For electrical measurements of the complex as insulator, sample in form of metal-insulator-semiconductor (MIS) structure was prepared and characterised by the measurement of the capacitance and AC-conductance as a function of gate voltage. From those measurements, the state density D_it at insulator/semiconductor interface and the density of the fixed charges in the complex film were determined. It was found that D_it was of order 10¹⁰ eV⁻¹/cm² and the surface charge density in the insulator film was of order 10¹⁰ cm⁻². The frequency dependence of the electrical conductivity and dielectric properties of MIS structures were studied at room temperature. It was observed that the experimental data follow the correlated barrier-hopping (CBH) model, from which the fundamental absorption edge, the cut off hopping distance, and other parameters of the model were determined. It was found that the capacitance of the complex increases as temperature increases. Generally, the present study shows that the tris(acetylacetonato)iron(III) films grown on p-Si is a promising candidate for low-k dielectric applications, it displays low-k value around 2.0.     

Synthesis and properties of a new copper(II)-hafnium phosphate Cu0.5Hf2(PO4)3

Phosphates of general formula M_0.5Hf₂(PO₄)₃ with M=Cd²⁺, Ca²⁺, Sr²⁺ and Cu²⁺ were prepared by coprecipitation and characterized by several physical techniques. The compounds containing Cd²⁺, Ca²⁺, Sr²⁺ belong to the Nasicon-type structure, whereas Cu_0.5Hf₂(PO₄)₃ exhibited substantially different DRX patterns. Combined temperature programmed reduction (TPR) and temperature-programmed oxidation (TPO) showed that the copper in Cu_0.5Hf₂(PO₄)₃ was distributed between two energetically different sites in proportions respectively equal to 40 and 60%. Electron Paramagnetic Resonance (EPR) investigations confirmed the TPR/TPO results and revealed that the two sites hosting the Cu²⁺ ions are of orthorhombic symmetry. Moreover, the Cu²⁺ ions might be reduced by hydrogen to Cu⁺. These results were also supported by the UV–visible studies that showed the disappearance, under reducing conditions, of the band corresponding to crystal field transitions of Cu²⁺ ions and the emergence of a new peak attributed to the transitions between (3d)¹⁰ and (3d)⁹(4s)¹ Cu⁺ levels. At the same time, IR spectroscopy confirmed that protons entered the open lattice framework of the material and gave rise to a new protonated phase containing monovalent copper Cu_0.5^IH_0.5Hf₂(PO₄)₃. This redox process was proven to be reversible without any subsequent change in the network of the phosphate.     

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.     

Preparation and characterisation of Au(1 1 0) and Cu(1 1 0) surfaces for applications in ambient environments

The preparation of metal surfaces that in ambient conditions are flat and smooth over micron length scales is desirable for a wide range of applications. Scanning probe microscopy (SPM) studies of biomolecular adsorption and cell attachment require such well-prepared substrates. Standard polishing finishes are often found to exhibit considerable roughness and damage including scratches when investigated by SPM. We have prepared by means of UHV technology Au(1 1 0) and Cu(1 1 0) surfaces that when in ambient air exhibit a more homogeneous morphology and are considerably smoother than conventional polished surfaces. SPM techniques and the optical technique of reflection anisotropy spectroscopy (RAS) are used to characterise the morphological and electronic properties of these surfaces, respectively. The RA response of both Au(1 1 0) and Cu(1 1 0) surfaces in ambient conditions can be interpreted in terms of optical transitions between surface-modified bulk bands.     

Preparation and characterization of poly(lactic acid)/poly(methyl methacrylate) blend tablets for application in quantitative analysis by micro Raman spectroscopy

Poly(lactic acid) (PLA) is a biodegradable polymer that has a variety of applications, one of which is as biomaterial in surgery or as functional layers on implants, due to its compatibility with living tissue. This paper reports the possibilities of quantification of poly(lactic acid) (PLA) in a polymer matrix such as poly(methyl methacrylate) (PMMA) by micro Raman spectroscopy (MRS). Blends of amorphous poly(DL‐lactic acid) with poly(methyl methacrylate) were prepared by the procedure of dissolution/precipitation. Thermal properties of the blends such as the glass transition temperature (Tg) were characterized by differential scanning calorimetry (DSC). The PLA/PMMA blends exhibited only a single glass transition region, indicating that this system is miscible. The PLA/PMMA system obeys the Gordon–Taylor equation (Tg versus PLA content). Various concentration ratios of PLA blends were prepared to use as a basis for quantitative analysis by MRS. Intensities of the characteristic bands at 813 cm⁻¹ (νCOC of PMMA) and 873 cm⁻¹ (νC―COO of PLA) were used for the calculation. The calibration graph showed a good linear correlation with an R² value of 0.9985. On the basis of the calibration curve obtained, the determined content of several PLA/PMMA blends was in good agreement when compared with nominal contents. The limit of detection (LOD) and quantification (LOQ) were calculated by the calibration data set as signal‐to‐noise method. The relative standard deviation of this method was lower than 10% and the accuracy better than 4%. This study demonstrated that Raman spectroscopy provides an alternative non destructive method for quantitative analysis of PLA in a PMMA matrix. Copyright © 2015 John Wiley & Sons, Ltd.     

Synthesis and optical properties for crystals of a novel organic semiconductor [ Ni(Cl) 2{(Ph 2P) 2CHC(R 1R 2)NHNH 2}]

In this investigation, the synthesis process of the apyrazole derivative for diphenylphosphino-methane hydrazine complexes [ Ni(Cl)₂{(Ph₂P)₂CHC(R₁R₂)NHNH₂}] was reported, and the obtained crystals were analyzed by X-ray diffraction. As a result of the growth process, a set of complexes were formed. The structures of these complexes are discussed on the basis of Elemental analysis (EA), IR, ¹H-NMR, ³¹P-NMR spectroscopic data and FAB mass spectra. The compound under investigation shows typical semiconductor behavior as a result of delocalization of the π-electrons in the structure. The reflectance and transmittance spectra for the crystals were measured and analyzed in the incident photon energy range 1.29 to 3.93 eV and in the temperature range 77 to 300 K. The optical study revealed that the optical transition is direct allowed. Below the absorption edge, the refractive index as a function of wavelength was determined in the low energy region of the used incident photon energy range. From the refractive index-wavelength variations, the oscillator and dispersion energies of the refractive index for the obtained crystals were determined. The static refractive index and static dielectric constant were evaluated.     

Validating fin tissue as a non-lethal proxy to liver and muscle tissue for stable isotope analysis of yellow perch (Perca flavescens)

Stable isotope ecology typically involves sacrificing the animal to obtain tissues. However, with threatened species or in long-term longitudinal studies, non-lethal sampling techniques should be used. The objectives of this study were to (1) determine if caudal fin tissue could be used as a non-lethal proxy to liver and muscle for stable isotope analysis, and (2) assess the effects of ethanol preservation on δ¹⁵N and δ¹³C in fin tissue of juvenile yellow perch Perca flavescens. The δ¹³C of caudal fin was not significantly different from liver (t₂₃?=??0.58; p?=?0.57), and was more correlated with δ¹⁵N in liver (r²?=?0.78) than muscle (r²?=?0.56). Ethanol preservation enriched ¹⁵N and ¹³C for caudal fins, but by using our developed regression models, these changes in δ¹⁵N and δ¹³C can now be corrected. Overall, caudal fin tissue is a more reliable proxy to liver than muscle for δ¹⁵N and δ¹³C in yellow perch.     

Design, simulation and structural optimization of a longitudinal acoustic resonator for trace gas detection using laser photoacoustic spectroscopy (LPAS)

The design of the acoustic resonator is critical for the optimization of the sensitivity of laser photoacoustic spectroscopy (LPAS) in trace gas detection applications. In this paper, an LC circuit model is used for the simulation of a 1D acoustic resonator. This acoustic resonator is designed for CO photoacoustic spectroscopy. The effects of the structural parameters, quality factor and resonant frequency on the performance of the device are theoretically analyzed. The role of the buffer volume as an acoustic filter is investigated and optimized dimensions of the buffer volume, to achieve minimum noise transmission coefficient, are calculated. The effects of the ambient temperature, variety of pressure and gas flow velocity on the resonant frequency of photoacoustic resonator and PA signal are simulated. The temperature dependence of the microphone sensitivity is also introduced.     

Preparation and in vitro evaluation of poly(D,L-lactide-co-glycolide) air-filled nanocapsules as a contrast agent for ultrasound imaging

The aim of this study was to prepare air-filled nanocapsules intended ultrasound contrast agents (UCAs) with a biodegradable polymeric shell composed of poly(d,l-lactide-co-glycolide) (PLGA). Because of their size, current commercial UCAs are not capable of penetrating the irregular vasculature that feeds growing tumors. The new generation of UCAs should be designed on the nanoscale to enhance tumor detection, in addition, the polymeric shell in contrast with monomolecular stabilized UCAs improves the mechanical properties against ultrasound pressure and lack of stability. The preparation method of air-filled nanocapsules was based on a modification of the double-emulsion solvent evaporation technique. Air-filled nanocapsules with a mean diameter of 370 ± 96 nm were obtained. Electronic microscopies revealed spherical-shaped particles with smooth surfaces and a capsular morphology, with a shell thickness of ∼50 nm. Air-filled nanocapsules showed echogenic power in vitro, providing an enhancement of up to 15 dB at a concentration of 0.045 mg/mL at a frequency of 10 MHz. Loss of signal for air-filled nanocapsules was 2 dB after 30 min, suggesting high stability. The prepared contrast agent in this work has the potential to be used in ultrasound imaging.     

Raman spectroscopy at different excitation wavelengths (1064, 785 and 532 nm) as a tool for diagnosis of colon cancer

Raman spectroscopy is structure sensitive non‐destructive method that allows observing the status of biological tissues with minimal impact. This method has a great potential in the diagnosis of various types of degenerative diseases including cancer damages. Near‐infrared Fourier transform (NIR‐FT)‐Raman (λ_ex ~1064 nm), NIR‐visible (Vis)‐Raman (λ_ex ~785 nm) and Vis‐Raman (λ_ex ~532 nm) spectra of normal and colorectal carcinoma colon tissue samples were recorded in macroscopic mode at 10–20 randomly chosen independent sites. In the cases of NIR‐Vis‐ and Vis‐Raman spectra, enhanced resonance effects were observed for tissue chromophores absorbing in the visible area. Evident spectral differences were noticed for Raman spectra of normal colon tissue samples in comparison with abnormal samples. The average Raman spectra of colon tissue samples were analysed by principal component analysis (PCA) to discriminate normal and abnormal tissues. PCA of combined dataset containing Raman intensities of chosen NIR‐FT, NIR‐Vis or Vis‐Raman bands led to discrimination of normal and abnormal colon tissue samples. Therefore, combination of these three Raman methods can be helpful for recognizing cancer lesions in colon for diagnostic purposes. Copyright © 2014 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.     

Composite coating of 58S bioglass and hydroxyapatite on a poly (ethylene terepthalate) artificial ligament graft for the graft osseointegration in a bone tunnel

The purpose of this study was to determine the effect of the combination of hydroxyapatite (HA) and bioglass (BG) on polyethylene terephthalate (PET) artificial ligament graft osseointegration within the bone tunnel. The results of in vitro culturing of MC3T3-E1 mouse osteoblastic cells proved that this HA/BG composite coating can promote the cell compatibility of grafts. A rabbit extraarticular tendon-to-bone healing model was used to evaluate the effect of this composite coating on PET artificial ligaments in vivo. The final results demonstrated that HA/BG coating improved new bone formation at the graft-bone interface and increased the load-to-failure property of graft in bone tunnel compared to the control group at early time. The study has shown that HA/BG composite coating on the PET artificial ligament surface has a positive effect in the induction of artificial ligament osseointegration within the bone tunnel.