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

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

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

Thymic Dendritic Cells Express Inducible Nitric Oxide Synthase and Generate Nitric Oxide in Response to Self- and Alloantigens

Thymocytes maturing in the thymus undergo clonal deletion/apoptosis when they encounter self- or allo-Ags presented by dendritic cells (DCs). How this occurs is a matter of debate, but NO may play a role given its ability of inducing apoptosis of these cells. APC (a mixed population of macrophages (Mφ) and DCs) from rat thymus expressed high levels of inducible NO synthase (iNOS) and produced large amounts of NO in basal conditions whereas iNOS expression and NO production were very low in thymocytes. Analysis by FACS and by double labeling of cytocentrifuged preparations showed that DCs and MΦ both express iNOS within APC. Analysis of a purified preparation of DCs confirmed that these cells express high levels of iNOS and produce large amounts of NO in basal conditions. The capacity of DCs to generate NO was enhanced by exposure to rat albumin, a self-protein, and required a fully expressed process of Ag internalization, processing, and presentation. Peptides derived from portions of class II MHC molecules up-regulate iNOS expression and NO production by DCs as well, both in self and allogeneic combinations, suggesting a role of NO in both self and acquired tolerance. We also found that NO induced apoptosis of rat double-positive thymocytes, the effect being more evident in anti-CD3-stimulated cells. Altogether, the present findings might suggest that DC-derived NO is at least one of the soluble factors regulating events, in the thymus, that follow recognition of self- and allo-Ags

Raman spectroscopy of graphene and bilayer under biaxial strain: bubbles and balloons

In this letter we use graphene bubbles to study the Raman spectrum of graphene under biaxial (e.g. isotropic) strain. Our Gruneisen parameters are in excellent agreement with the theoretical values. Discrepancy in the previously reported values is attributed to the interaction of graphene with the substrate. Bilayer balloons (intentionally pressurized membranes) have been used to avoid the effect of the substrate and to study the dependence of strain on the inter-layer interactions.Comment: 14 pages, 4 figure