1,251 research outputs found
Raman Fingerprint of Charged Impurities in Graphene
We report strong variations in the Raman spectra for different single-layer
graphene samples obtained by micromechanical cleavage, which reveals the
presence of excess charges, even in the absence of intentional doping. Doping
concentrations up to ~10^13 cm-2 are estimated from the G peak shift and width,
and the variation of both position and relative intensity of the second order
2D peak. Asymmetric G peaks indicate charge inhomogeneity on the scale of less
than 1 micron.Comment: 3 pages, 5 figure
Fish fillet authentication by image analysis
The work aims at developing an image analysis procedure able to distinguish high value fillets of Atlantic
cod (Gadus morhua) from those of haddock (Melanogrammus aeglefinus). The images of fresh G. morhua
(n \ubc 90) and M. aeglefinus (n \ubc 91) fillets were collected by a flatbed scanner and processed at different
levels. Both untreated and edge-based segmented (Canny algorithm) regions of interest were submitted
to surface texture evaluation by Grey Level Co-occurrence Matrix analysis. Twelve surface texture variables
selected by Principal Component Analysis or by SELECT algorithm were then used to develop Linear
Discriminant Analysis models. An average correct classification rate ranging from 86.05 to 92.31% was
obtained in prediction, irrespective the use of raw or segmented images. These findings pave the way for
a simple machine vision system to be implemented along fish market chain, in order to provide
stakeholders with a simple, rapid and cost-effective system useful in fighting commercial frauds
The Raman Fingerprint of Graphene
Graphene is the two-dimensional (2d) building block for carbon allotropes of
every other dimensionality. It can be stacked into 3d graphite, rolled into 1d
nanotubes, or wrapped into 0d fullerenes. Its recent discovery in free state
has finally provided the possibility to study experimentally its electronic and
phonon properties. Here we show that graphene's electronic structure is
uniquely captured in its Raman spectrum that clearly evolves with increasing
number of layers. Raman fingerprints for single-, bi- and few-layer graphene
reflect changes in the electronic structure and electron-phonon interactions
and allow unambiguous, high-throughput, non-destructive identification of
graphene layers, which is critically lacking in this emerging research area
Raman Spectroscopy of Graphene Edges
Graphene edges are of particular interest since their orientation determines the electronic properties. Here we present a detailed Raman investigation of graphene flakes with edges oriented at different crystallographic directions. We also develop a real space theory for Raman scattering to analyze the general case of disordered edges. The position, width, and intensity of G and D peaks are studied as a function of the incident light polarization. The D-band is strongest for polarization parallel to the edge and minimum for perpendicular. Raman mapping shows that the D peak is localized in proximity of the edge. For ideal edges, the D peak is zero for zigzag orientation and large for armchair, allowing in principle the use of Raman spectroscopy as a sensitive tool for edge orientation. However, for real samples, the D to G ratio does not always show a significant dependence on edge orientation. Thus, even though edges can appear macroscopically smooth and oriented at well-defined angles, they are not necessarily microscopically ordered
tuppence-based SERS for the detection of illicit materials
Deposition of silver onto British 2p coins has been demonstrated as an
efficient and cost effective approach to producing substrates capable of
promoting surface enhanced Raman scattering (SERS). Silver application to the
copper coins is undemanding taking just 20 s, and results in the formation of
multiple hierarchial dendritic structures. To demonstrate that the silver
deposition sites were capable of SERS the highly fluorescent Rhodamine 6G
(R6G) probe was used. Analyses indicated that Raman enhancement only occurs at
the silver deposition sites and not from the roughened copper surface. The
robustness of the substrate in the identification and discrimination of
illegal and legal drugs of abuse was then explored. Application of the drugs
to the substrates was carried out using spotting and soaking methodologies.
Whilst little or no SERS spectra of the drugs were generated upon spotting,
soaking of the substrate in a methanolic solution of the drugs yielded a vast
amount of spectral information. Excellent reproducibility of the SERS method
and classification of three of the drugs, 4-methylmethcathinone (mephedrone),
5,6-methylenedioxy-2-aminoindane (MDAI) and
3,4-methylenedioxy-N-methylamphetamine (MDMA) were demonstrated using
principal components analysis and partial least squares
Emulsion versus nanoemulsion : how much is the formulative shift critical for a cosmetic product?
The use of nanoemulsions in cosmetic products has been enlarged in the last decades because of several formulative advantages (e.g., the improved self-life stability, better texture properties). In addition, nanoemulsions seemed to improve the penetration of active ingredients through the human skin, comparing to conventional emulsion. In this contest, the risk of a higher systemic exposure of consumer to active ingredients, due to the ability of nanoemulsion to enhance permeation, results a critical attribute that should be evaluated for assuring the consumer safety. The aim of this work was the evaluation of how an oil-in-water (O/W) nanoemulsion can influence the in vitro skin permeation profiles of two model active ingredients with different polarity (i.e., caffeine and ethyl ximenynate). Preliminarily, since both selected molecules influenced the physical stability of nanoemulsion, formulative studies were carried out to identify the most stable formulation to perform in vitro permeation studies. The overall results demonstrated that nanoemulsions could significantly influence the permeation profiles of molecules as a function of their physicochemical properties. In particular, O/W nanoemulsions significantly improved the permeation profiles of apolar active ingredients in comparison to conventional emulsions, whereas no differences were observable for polar molecules. Considering such findings, it is worth observing that there is room for reconsidering the risk assessment of nanoemulsion-based cosmetic products
Mucoadhesive budesonide formulation for the treatment of eosinophilic esophagitis
Eosinophilic esophagitis (EE) is a chronic immune/antigen-mediated esophageal inflammatory disease for which off-label topical corticosteroids (e.g., budesonide) are widely used in clinic. In general, thickening excipients are mixed with industrial products to improve the residence time of the drug on the esophageal mucosa. The compounding procedures are empirical and the composition is not supported by real physicochemical and technological characterization. The current study aimed to propose a standardized budesonide oral formulation intended to improve the resistance time of the drug on the esophageal mucosa for EE treatment. Different placebo and drug-loaded (0.025% w/w) formulations were prepared by changing the percentage of xanthan gum alone or in ratio 1:1 with guar gum. Both excipients were added in the composition for their mucoadhesive properties. The formulative space was rationalized based on the drug physicochemical stability and the main critical quality attributes of the formulation, e.g., rheological properties, syringeability, mucoadhesiveness and in vitro penetration of budesonide in porcine esophageal tissue. The obtained results demonstrated that gums allowed a prolonged residence time. However, the concentration of the mucoadhesive polymer has to be rationalized appropriately to permit the syringeability of the formulation and, therefore, easy dosing by the patient/caregiver
Determination of the geographical origin of green coffee beans using NIR spectroscopy and multivariate data analysis
In this work, near infrared (NIR) spectroscopy and multivariate data analysis were investigated as a fast and non disruptive method to classify green coffee beans on continents and countries bases. FT-NIR spectra of 191 coffee samples, origin from 2 continents and 9 countries, were acquired by two different laboratories.
Laboratory-independent Partial Least Square-Discriminant Analysis and interval PIS-DA models were developed by following a hierarchical approach, i.e. considering at first the continent and then the country of origin as discrimination rule.
The best continent-based classification model was able to identify correctly more than 98% in prediction, whereas 100% of them were correctly predicted by the best country-based classification model. The inter-laboratory reliability of the proposed method was confirmed by McNemar test, since no significant differences (P > 0.05) were found. Furthermore, a validation was performed predicting the spectral test set of a laboratory using the model developed by the other one
Preserving the Integrity of Liposomes Prepared by Ethanol Injection upon Freeze-Drying: Insights from Combined Molecular Dynamics Simulations and Experimental Data
The freeze-drying of complex formulations, such as liposomes, is challenging, particularly if dispersions contain residual organic solvents. This work aimed to investigate the effects of possible protectants, namely sucrose, trehalose and/or poly(vinyl pyrrolidone) (PVP), on the main features of the dried product using a 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC)-based liposomal dispersion prepared by ethanol injection and containing ethanol up to 6%, as a model. The interactions among vesicles and protectants were preliminary screened by Molecular Dynamics (MD) simulations, which have been proved useful in rationalizing the selection of protectant(s). The freeze-drying protocol was based on calorimetric results. Overall data suggested a stronger cryo-protectant effect of trehalose, compared with sucrose, due to stronger interactions with the DPPC bilayer and the formation of highly ordered clusters around the lipids. The effect further improved in the presence of PVP. Differently from the other tested protectants, the selected trehalose/PVP combination allows to preserve liposome size, even in the presence of 6% ethanol, as demonstrated by Nanoparticle Tracking Analysis (NTA). Nevertheless, it should be also underlined that cakes blew out at an ethanol concentration higher than 1% v/v, probably due to the poor cohesion within the cake and solvent vapour pressure upon sublimation
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