Surface-enhanced Raman spectroscopy of novel psychoactive substances using polymer-stabilized Ag nanoparticle aggregates

A set of seized "legal high'' samples and pure novel psychoactive substances have been examined by surface-enhanced Raman spectroscopy using polymer-stabilized Ag nanoparticle (Poly-SERS) films. The films both quenched fluorescence in bulk samples and allowed identification of mu g quantities of drugs collected with wet swabs from contaminated surfaces.

Preaggregated Ag Nanoparticles in Dry Swellable Gel Films for Off-the-Shelf Surface-Enhanced Raman Spectroscopy

Large, thin (50 mu m) dry polymer sheets containing numerous surface-enhanced Raman spectroscopy (SERS) active Ag nanopartide aggregates have been prepared by drying aqueous mixtures of hydroxyethylcelloulose (HEC) and preaggregated Ag colloid in 10 x 10 cm molds. In these dry films, the particle aggregates are protected from the environment during storage and are easy to handle; for example, they can be cut to size with scissors. When in use, the highly swellable HEC polymer allowed the films to rapidly absorb aqueous analyte solutions while simultaneously releasing the Ag nanoparticle aggregates to interact with the analyte and generate large SERS signals. Either the films could be immersed in the analyte solution or 5 mu L droplets were applied to the surface; in the latter method, the local swelling caused the active area to dome upward, but the swollen film remained physically robust and could be handled as required. Importantly, encapsulation and release did not significantly compromise the SERS performance of the colloid; the signals given by the swollen films were similar to the very high signals obtained from the parent citrate-reduced colloid and were an order of magnitude larger than a commercially available nanoparticle substrate. These "Poly-SERS" films retained 70% of their SERS activity after being stored for 1 year in air. The films were sufficiently homogeneous to give a standard deviation of 3.2% in the absolute signal levels obtained from a test analyte, primarily due to the films' ability to suppress "coffee ring" drying marks, which meant that quantitative analysis without an internal standard was possible. The majority of the work used aqueous thiophenol as the test analyte; however, preliminary studies showed that the Poly-SERS films could also be used with nonaqueous solvents and for a range of other analytes including theophylline, a therapeutic drug, at a concentration as low as 1.0 x 10(-5) mol dm(-3) (1.8 mg/dm(3)), well below the sensitivity required for theophylline monitoring where the target range is 10-20 mg/dm(3).

Investigation of the chemical origin and evidential value of differences in the SERS spectra of blue gel inks

Highly swellable polymer films doped with Ag nanoparticle aggregates (poly-SERS films) have been used to record very high signal:noise ratio, reproducible surface-enhanced (resonance) Raman (SER(R)S) spectra of in situ dried ink lines and their constituent dyes using both 633 and 785 nm excitation. These allowed the chemical origins of differences in the SERRS spectra of different inks to be determined. Initial investigation of pure samples of the 10 most common blue dyes showed that the dyes which had very similar chemical structures such as Patent Blue V and Patent Blue VF (which differ only by a single OH group) gave SERRS spectra in which the only indications that the dye structure had been changed were small differences in peak positions or relative intensities of the bands. SERRS studies of 13 gel pen inks were consistent with this observation. In some cases inks from different types of pens could be distinguished even though they were dominated by a single dye such as Victoria Blue B (Zebra Surari) or Victoria Blue BO (Pilot Acroball) because their predominant dye did not appear in other inks. Conversely, identical spectra were also recorded from different types of pens (Pilot G7, Zebra Z-grip) because they all had the same dominant Brilliant Blue G dye. Finally, some of the inks contained mixtures of dyes which could be separated by TLC and removed from the plate before being analysed with the same poly-SERS films. For example, the Pentel EnerGel ink pen was found to give TLC spots corresponding to Erioglaucine and Brilliant Blue G. Overall, this study has shown that the spectral differences between different inks which are based on chemically similar, but nonetheless distinct dyes, are extremely small, so very close matches between SERRS spectra are required for confident identification. Poly-SERS substrates can routinely provide the very stringent reproducibility and sensitivity levels required. This, coupled with the awareness of the reasons underlying the observed differences between similarly coloured inks allows a more confident assessment of the evidential value of inks SERS and should underpin adoption of this approach as a routine method for the forensic examination of inks.

Highly Sensitive, Uniform, and Reproducible Surface-Enhanced Raman Spectroscopy from Hollow Au-Ag Alloy Nanourchins

A hierarchical nanoparticle strategy to simultaneously gain super Raman signal amplification, high uniformity, and reproducibility is presented. Using hollow Au-Ag alloy nanourchins, an ultrahigh sensitivity, e.g., down to 1 fM concentrations for DEHP molecule is obtained. A small standard deviation of <10% is achieved by simply dropping and evaporating sub-100 nm nanourchins onto a substrate.

An investigation of the thermal stability and sulphur tolerance of Ag/Y-Al2O3 catalysts for the SCR of NOx with hydrocarbons and hydrogen

The sulphur tolerance and thermal stability of a 2 wt% Ag/gamma-Al2O3 catalyst was investigated for the H-2-promoted SCR of NO, with octane and toluene. The aged catalyst was characterised by XRD and EXAFS analysis. It was found that the effect of ageing was a function of the gas mix and temperature of ageing. At high temperatures (800 degrees C) the catalyst deactivated regardless of the reaction mix. EXAFS analysis showed that this was associated with the Ag particles on the surface of the catalyst becoming more ordered. At 600 and 700 degrees C, the deactivating effect of ageing was much less pronounced for the catalyst in the H-2-promoted octane-SCR reaction and ageing at 600 degrees C resulted in an enhancement in activity for the reaction in the absence of H-2. For the toluene + H-2-SCR reaction the catalyst deactivated at each ageing temperature. The effect of addition of low levels of sulphur (1 ppm SO2) to the feed was very much dependent on the reaction temperature. There was little deactivation of the catalyst at low temperatures ( 500 degrees C). The results can be explained by the activity of the catalyst for the oxidation Of SO2 to SO3 and the relative stability of silver and aluminium sulphates. The catalyst could be almost fully regenerated by a combination of heating and the presence of hydrogen in the regeneration mix. The catalyst could not be regenerated in the absence of hydrogen. (c) 2006 Published by Elsevier B.V.

Theoretical considerations of electrochemical phase formation for an ideal Frank-van der Merwe system - Ag on Au(111) and Au(100)

: Static calculation and preliminary kinetic Monte Carlo simulation studies are undertaken for the nucleation and growth on a model system which follows a Frank-van der Merwe mechanism. In the present case, we consider the deposition of Ag on Au(100) and Au(111) surfaces. The interactions were calculated using the embedded atom model. The kinetics of formation and growth of 2D Ag structures on Au(100) and Au(111) is investigated and the influence of surface steps on this phenomenon is studied. Very different time scales are predicted for Ag diffusion on Au(100) and Au(111), thus rendering very different regimes for the nucleation and growth of the related 2D phases. These observations are drawn from the application of a model free of any adjustable parameter.

Rotation of a nanoparticle cloud in an inductively coupled plasma induced by weak static magnetic fields

Hydrocarbon nanoparticles with diameters between 10 and 30 nanometres are created in a low pressure plasma combining capacitive and inductive power coupling. The particles are generated in the capacitive phase of the experiment and stay confined in the plasma in the inductive phase. The presence of these embedded particles induces a rotation of a particle-free region (void) around the symmetry axis of the reactor. The phenomenon is analysed using optical emission spectroscopy both line integrated and spatially resolved via an intensified charge coupled device camera. From these data, electron temperatures and densities are deduced. We find that the rotation of the void is driven by a tangential component of the ion drag force induced by an external static magnetic field. Two modes are observed: a fast rotation of the void in the direction opposite to that of the tangential component and a slow rotation in the same direction. The rotation speed decreases linearly with the size of the particles. In the fast mode the dependence on the applied magnetic field is weak and consequently the rotation speed can serve as a monitor to detect particle sizes in low temperature plasmas.

Electrochemical kinetics of Ag vertical bar Ag+ and TMPD vertical bar TMPD+center dot in the room-temperature ionic liquid [C(4)mpyrr][NTf2]; toward optimizing reference electrodes for voltammetry in RTILs

The voltammetry and kinetics of the Ag vertical bar Ag+ system (commonly used as a reference electrode material in both protic/aprotic and RTIL solvents) was studied in the room-temperature ionic liquid N-butyl-N-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide, [C(4)mpyrr][NTf2] on a 10 mu m diameter Pt electrode. For the three silver salts investigated (AgOTf, AgNTf2, and AgNO3, where OTf- = trifluoromethanesulfonate, NTf2- = bis(trifluoromethylsulfonyl)imide, and NO3- = nitrate), the voltammetry gave rise to a redox couple characteristic of a

Rapid, quantitative analysis of ppm/ppb nicotine using surface-enhanced Raman scattering from polymer-encapsulated Ag nanoparticles (gel-colls)

Rapid, quantitative SERS analysis of nicotine at ppm/ppb levels has been carried out using stable and inexpensive polymer-encapsulated Ag nanoparticles (gel-colls). The strongest nicotine band (1030 cm(-1)) was measured against d(5)-pyridine internal standard (974 cm(-1)) which was introduced during preparation of the stock gel-colls. Calibration plots of I-nic/I-pyr against the concentration of nicotine were non-linear but plotting I-nic/I-pyr against [nicotine](x) (x = 0.6-0.75, depending on the exact experimental conditions) gave linear calibrations over the range (0.1-10 ppm) with R-2 typically ca. 0.998. The RMS prediction error was found to be 0.10 ppm when the gel-colls were used for quantitative determination of unknown nicotine samples in 1-5 ppm level. The main advantages of the method are that the gel-colls constitute a highly stable and reproducible SERS medium that allows high throughput (50 sample h(-1)) measurements.

On the nature of the silver phases of Ag/Al2O3 catalysts for reactions involving nitric oxide

The nature of the silver phases of Ag/Al2O3 catalysts (prepared by silver nitrate impregnation followed by calcination) was investigated by X-ray diffractograms (XRD), transmission electron microscopy (TEM) and UV-VIS analyses and related to the activity of the corresponding materials for the oxidation of NO to NO2. The UV-VIS spectrum of the 1.2 wt.% Ag/Al2O3 exhibited essentially one band associated with Ag+ species and the NO2 yields measured over this material were negligible. A 10 wt.% Ag/Al2O3 material showed the presence of oxidic species of silver (as isolated Ag+ cations and silver aluminate), but the UV-VIS data also revealed the presence of some metallic silver. The activity for the NO oxidation to NO2 of this sample was moderate. The same 10% sample either reduced in H-2 or used for the C3H6-selective catalytic reduction (SCR) of NO showed a significantly larger proportion of silver metallic phases and these samples displayed a high activity for the formation of NO2. These data show that the structure and nature of the silver phases of Ag/Al2O3 catalysts can markedly change under reaction feed containing only a fraction of reducing agent (i.e. 500 ppm of propene) in net oxidizing conditions (2.5% O-2). The low activity for N-2 formation during the C3H6-SCR of NO (reported in an earlier study) over the high loading sample can. therefore, he related to the presence of metallic silver. which is yet a good catalyst for NO oxidation to NO2. The reverse observations apply for the oxide species observed over the low loading sample, which is a good SCR catalyst but do not oxidize NO to NO2. (C) 2002 Elsevier Science B.V. All rights reserved.

Chitosan nanoparticle as protein delivery carrier - Systematic examination of fabrication conditions for efficient loading and release

Chitosan nanoparticles fabricated via different preparation protocols have been in recent years widely studied as carriers for therapeutic proteins and genes with varying degree of effectiveness and drawbacks. This work seeks to further explore the polyionic coacervation fabrication process, and associated processing conditions under which protein encapsulation and subsequent release can be systematically and predictably manipulated so as to obtain desired effectiveness. BSA was used as a model protein which was encapsulated by either incorporation or incubation method, using the polyanion tripolyphosphate (TPP) as the coacervation crosslink agent to form chitosan-BSA-TPP nanoparticles. The BSA-loaded chitosan-TPP nanoparticles were characterized for particle size, morphology, zeta potential, BSA encapsulation efficiency, and subsequent release kinetics, which were found predominantly dependent on the factors of chitosan molecular weight, chitosan concentration, BSA loading concentration, and chitosan/TPP mass ratio. The BSA loaded nanoparticles prepared under varying conditions were in the size range of 200-580 nm, and exhibit a high positive zeta potential. Detailed sequential time frame TEM imaging of morphological change of the BSA loaded particles showed a swelling and particle degradation process. Initial burst released due to surface protein desorption and diffusion from sublayers did not relate directly to change of particle size and shape, which was eminently apparent only after 6 h. It is also notable that later stage particle degradation and disintegration did not yield a substantial follow-on release, as the remaining protein molecules, with adaptable 3-D conformation, could be tightly bound and entangled with the cationic chitosan chains. In general, this study demonstrated that the polyionic coacervation process for fabricating protein loaded chitosan nanoparticles offers simple preparation conditions and a clear processing window for manipulation of physiochemical properties of the nanoparticles (e.g., size and surface charge), which can be conditioned to exert control over protein encapsulation efficiency and subsequent release profile. The weakness of the chitosan nanoparticle system lies typically with difficulties in controlling initial burst effect in releasing large quantities of protein molecules. (C) 2007 Elsevier B.V. All rights reserved.

In-situ FT-IR spectroscopic studies of fuel cell electro-catalysis: From single-crystal to nanoparticle surfaces

The work presented in this article shows the power of the variable temperature, in-situ FT-IR spectroscopy system developed in Newcastle with respect to the investigation of fuel cell electro-catalysis. On the Ru(0001) electrode surface, CO co-adsorbs with the oxygen-containing adlayers to form mixed [CO+(2x2)-O(H)] domains. The electro-oxidation of the Ru(0001) surface leads to the formation of active (1x1)-O(H) domains, and the oxidation of adsorbed CO then takes place at the perimeter of these domains. At 20 degrees C, the adsorbed CO is present as rather compact islands. In contrast, at 60 degrees C, the COads is present as a relatively looser and weaker adlayer. Higher temperature was also found to facilitate the surface diffusion and oxidation of COads. No dissociation or electro-oxidation of methanol was observed at potentials below approximately 950mV; however, the Ru(0001) surface at high anodic potentials was observed to be very active. On both Pt and PtRu nanoparticle surfaces, only one linear bond CO adsorbate was formed from methanol adsorption, and the PtRu surface significantly promoted both methanol dissociative adsorption to CO and its further oxidation to CO2. Increasing temperature from 20 to 60 degrees C significantly facilitates the methanol turnover to CO2.