This review focuses on recent developments in hybrid and nanostructured substrates for SERS (surface-enhanced Raman scattering) studies. Thus substrates composed of at least two distinct types of ...materials, in which one is a SERS active metal, are considered here aiming at their use as platforms for chemical detection in a variety of contexts. Fundamental aspects related to the SERS effect and plasmonic behaviour of nanometals are briefly introduced. The materials described include polymer nanocomposites containing metal nanoparticles and coupled inorganic nanophases. Chemical approaches to tailor the morphological features of these substrates in order to get high SERS activity are reviewed. Finally, some perspectives for practical applications in the context of chemical detection of analytes using such hybrid platforms are presented.
A perspective of recent developments on nanostructures composed of hybrid materials for SERS applications, including Chemical detection of analytes.
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•It is essential to monitor polymorphic transformations induced by the thermal instability of poorly water-soluble drugs.•Raman imaging with CA as a powerful tool to monitor ...polymorphic changes and degradation products in APIs.•Raman imaging provides a global overview (image) and spectral profile in each pixel (Raman spectrum).
Raman imaging methods have appeared in the last years as a powerful approach to monitoring the quality of pharmaceutical compounds. Because polymorphism occurs in many crystalline pharmaceutical compounds, it is essential to monitor polymorphic transformations induced by different external stimulus, such as temperature changes, to which those compounds may be submitted. Raman imaging with k-means cluster analysis (CA) is used here as an essential technique to investigate structural and chemical transformations occurring in carbamazepine p-monoclinic (CBZ III) into carbamazepine triclinic (CBZ I) when submitted to temperatures near the melting point of CBZ III (178 °C) and CBZ I (193 °C).
CBZ III commercial powder and laboratorial prepared CBZ I were analyzed by differential scanning calorimetry, powder X-ray diffraction and Raman spectroscopy with variable temperature. After thermal treatment, the resultant CBZ powder was evaluated by Raman imaging, in which all imaging data was analyzed using CA. Raman imaging allowed the identification of different polymorphs of CBZ (CBZ III and CBZ I) and iminostilbene (IMS), a degradation product of CBZ, in the treated samples, depending on the heating treatment method.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPUK, ZAGLJ, ZRSKP
Gravity currents produced by full-depth lock-release of saline water into a fresh water tank are studied focusing on the influence of the initial density of the saline mixture in the lock and the bed ...roughness on gravity current kinematics. Temporal evolution of the current front position and front velocity are analysed and related to different phases of the current. Time-space evolution of current depth-averaged density and current height are assessed as well. Roughness of the channel bed plays an important role in the current kinematics, particularly in decreasing the front velocity due to extra drag at the bed. The analysis of Froude numbers, estimated with the initial and local reduced gravity and established with different length scales of the current, allow for the definition of the important variables and current dynamics of each phase of the current development.
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BFBNIB, GIS, IJS, KISLJ, NUK, PNG, UL, UM, UPUK
Fast detection of contaminants of emerging concern (CECs) in water resources is of great environmental interest. Ideally, sustainable materials should be used in water quality monitoring technologies ...implemented for such purposes. In this regard, the application of bio-based materials aimed at the fabrication of analytical platforms has become of great importance. This research merges both endeavors by exploring the application of chitosan-coated paper, decorated with silver nanoparticles (AgNPs), on surface-enhanced Raman scattering (SERS) spectroscopy studies of two distinct types of CECs dissolved in aqueous samples: an antibiotic (ciprofloxacin) and a pesticide (thiram). Our results indicate the superior SERS performance of biocoated substrates compared to their non-coated paper counterparts. The detection limits achieved for thiram and ciprofloxacin using the biocoated substrates were 0.024 ppm and 7.7 ppm, respectively. The efficient detection of both analytes is interpreted in terms of the role of the biopolymer in promoting AgNPs assemblies that result in local regions of enhanced SERS activity. Taking advantage of these observations, we use confocal Raman microscopy to obtain Raman images of the substrates using ciprofloxacin and thiram as molecular probes. We also demonstrate that these biobased substrates can be promising for on-site analysis when used in conjunction with portable Raman instruments.
Contaminants of emerging concern present in water can be monitored using Ag/chitosan paper-based SERS substrates.
A series of nanocomposites based on polyamide (NL16, PA) filter membranes containing metal nanoparticles (NPs) have been prepared by filtration under reduced pressure of the metal colloids. The ...ensuing materials were then investigated as substrates for surface-enhanced Raman scattering (SERS) imaging studies envisaging the spectroscopic detection of vestigial organic pollutants dissolved in contaminated water. The organic dye crystal violet (CV) was used here as a model pollutant because it is a hazardous compound present in certain effluent waters. Moreover this compound is well-known for its strong SERS activity, which is clearly advantageous in the context of material development for SERS. Indeed, several preparative strategies were employed to prepare PA-based composites, and the impact on SERS detection was investigated. These include the use of chemical and morphological distinct plasmonic NPs (Ag, Au), a variable metal load and changing the order of addition of the analytical specimens. These studies demonstrate that the parameters employed in the fabrication of the SERS substrates have a strong impact on the Raman signal enhancement. The use of Raman imaging during the fabrication process allows establishing improvements that translate to better performances of the substrates in the analyte detection. The results have been interpreted by considering an integrated set of operational parameters that include the affinity of CV molecules to the substrate, amount and dispersion of NPs in the PA membranes, and the detection method. Noteworthy the use of SERS analysis assisted with Raman imaging allowed achieving a detection limit for CV as low as 100 aM in ultrapure water and 10 fM in real samples.
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IJS, KILJ, NUK, PNG, UL, UM, UPUK
Graphene sheets, which possess unique nanostructure and a variety of fascinating properties, are considered as promising nanoscale building blocks of new nanocomposites, namely as a support material ...for the dispersion of metal nanoparticles. One of the methodologies used to prepare graphene sheets is the chemical exfoliation of graphite in aqueous medium, which produces oxygen functionalized graphene sheets. Here, we show that the presence of oxygen functionalities at the graphene surface provides reactive sites for the nucleation and growth of gold nanoparticles. Gold nanoparticles are effectively grown at functionalized graphene surfaces using a simple chemical method in aqueous medium. The nucleation and growth mechanism depends on the degree of oxygen functionalization at the graphene surface sheets, no gold nanoparticles are obtained at totally reduced graphene surfaces. Additionally, our studies indicate that the graphene/gold nanocomposites are potential substrates for SERS (surface enhanced Raman scattering) in particular for single gold nanoparticle SERS studies.
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IJS, KILJ, NUK, PNG, UL, UM
7.
Dynamics of the head of gravity currents Nogueira, Helena I. S.; Adduce, Claudia; Alves, Elsa ...
Environmental fluid mechanics (Dordrecht, Netherlands : 2001),
04/2014, Volume:
14, Issue:
2
Journal Article
Open access
The present work experimentally investigates the dynamics of unsteady gravity currents produced by lock-release of a saline mixture into a fresh water tank. Seven different experimental runs were ...performed by varying the density of the saline mixture in the lock and the bed roughness. Experiments were conducted in a Perspex flume, of horizontal bed and rectangular cross section, and recorded with a CCD camera. An image analysis technique was applied to visualize and characterize the current allowing thus the understanding of its general dynamics and, more specifically, of the current head dynamics. The temporal evolution of both head length and mass shows repeated stretching and breaking cycles: during the stretching phase, the head length and mass grow until reaching a limit, then the head becomes unstable and breaks. In the instants of break, the head aspect ratio shows a limit of 0.2 and the mass of the head is of the order of the initial mass in the lock. The average period of the herein called breaking events is seen to increase with bed roughness and the spatial periodicity of these events is seen to be approximately constant between runs. The rate of growth of the mass at the head is taken as a measure to assess entrainment and it is observed to occur at all stages of the current development. Entrainment rate at the head decreases in time suggesting this as a phenomenon ruled by local buoyancy and the similarity between runs shows independence from the initial reduced gravity and bed roughness.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Paper-based substrates containing dendrimer-stabilized Au:Ag:PAMAM nanoalloys for the SERS probing of the pesticide thiram in an aqueous solution.
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Research on paper substrates ...prepared by inkjet deposition of metal nanoparticles for sensing applications has become a hot topic in recent years; however, the design of such substrates based on the deposition of alloy nanoparticles remains less explored. Herein, we report for the first time the inkjet printing of dendrimer-stabilized colloidal metal nanoalloys for the preparation of paper substrates for surface-enhanced Raman scattering (SERS) spectroscopy. To this end, nanoassemblies containing variable molar ratios of Au:Ag were prepared in the presence of poly(amidoamine) dendrimer (PAMAM), resulting in plasmonic properties that depend on the chemical composition of the final materials. The dendrimer-stabilized Au:Ag:PAMAM colloids exhibit high colloidal stability, making them suitable for the preparation of inks for long-term use in inkjet printing of paper substrates. Moreover, the pre-treatment of paper with a polystyrene (PS) aqueous emulsion resulted in hydrophobic substrates with improved SERS sensitivity, as illustrated in the analytical detection of tetramethylthiuram disulfide (thiram pesticide) dissolved in aqueous solutions. We suggest that the interactions established between the two polymers (PAMAM and PS) in an interface region over the cellulosic fibres, resulted in more exposed metallic surfaces for the adsorption of the analyte molecules. The resulting hydrophobic substrates show long-term plasmonic stability with high SERS signal retention for at least ninety days.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPUK, ZAGLJ, ZRSKP
Anhydrous carbamazepine (CBZ) is an anti-convulsant drug commonly used to treat epilepsy and relieve trigeminal neuralgia. The presence of the dihydrate form in commercial CBZ tablets can change the ...dissolution rate of the active pharmaceutical ingredient (API), thus decreasing its activity. The hydration transformation can occur during wet granulation or storage, within a few weeks, depending on the ambient conditions. This work aims to investigate the effect of relative humidity (RH) in the transition of pure anhydrous CBZ (CBZ III) into the hydrate form by using confocal Raman microscopy with cluster analysis (CA). Firstly, several tablets of pure CBZ III containing different amounts of CBZ DH (50%, 10%, 1%, 0.5%) were prepared and analyzed by Raman imaging with CA. Our results show that CBZ DH crystals can be detected in the CBZ III tablets, at as low a concentration as 0.5%, giving distinct Raman features for the analysed polymorphs. The stability of pure anhydrous (CBZ III) tablets was then monitored by Raman imaging at room temperature (20-22 °C) and different RH (6%, 60% and 89%). The Raman imaging with CA showed that the anhydrous CBZ tablets start to convert into the hydrate form after 48 h, and it completely changes after 120 hours (5 days) at RH 89%. The tablets exposed to RH 6% and 60% did not demonstrate the presence of CBZ DH after 1 week of exposure. The exposure time was extended for 9 months in the former, and no CBZ DH was observed. A comparative study using IR imaging was also performed, demonstrating the viability of these vibrational imaging techniques as valuable tools to monitor the hydration process of active pharmaceutical ingredients.
The hydration mechanism of anhydrous carbamazepine, under different ambient conditions, is investigated here for the first time by complementary vibrational imaging techniques: confocal Raman microscopy and infrared imaging.
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