Understanding Surfactant Stabilization of MoS₂ Nanosheets in Aqueous Dispersions from Zeta Potential Measurements and Molecular Dynamics Simulations

The sonication-assisted exfoliation of MoS₂ in aqueous media in the presence of ionic surfactants to give stable dispersions is an attractive procedure for obtaining single or few-layered nanosheets, as it is easily scalable and does not involve toxic or high boiling solvents. Here, we have investigated the origin of the stability of aqueous dispersions of MoS₂ nanosheets obtained by sonication in the presence of the cationic surfactant cetyltrimethylammonium bromide (CTAB) by zeta potential measurements at different ionic strengths and molecular dynamics (MD) simulations. Our measurements show that the dispersions are stabilized by electrostatic repulsive interactions between the delaminated MoS₂ nanosheets, which acquire a positive charge because of the adsorption of the cationic surfactant. MD simulations were performed to understand the interaction between MoS₂ nanosheets and the CTAB surfactant chains in the dispersion and the structure and arrangement of the adsorbed surfactant chains. Our simulations are able to reproduce the experimentally measured variation of the zeta potential with ionic strength. In addition, the relative contribution and role of different intermolecular interactions between various components of the dispersion was estimated by simulating the potential of mean force (PMF) between two surfactant-adsorbed MoS₂ sheets. On the basis of experiment and simulations, we are able to establish that the stability of aqueous dispersions of MoS₂ in the presence of an ionic surfactant can be understood based on classical models of charged interfaces

Liquid-Phase Exfoliation of MoS₂ Nanosheets: The Critical Role of Trace Water

Sonication-assisted liquid-phase exfoliation of layered materials in suitable organic solvents offers a simple scalable route for the production of 2D nanomaterials. <i>N</i>-methyl-2-pyrrolidone (NMP) is one of the most efficient solvents for liquid-phase exfoliation of a variety of layered solids, including MoS₂. We show here that trace water present in NMP is crucial for the stability of MoS₂ nanosheets in NMP dispersions. In the absence of water, the sheets are fragmented and chemically unstable. Using solution NMR techniques, 2D nuclear Overhauser effect and spin–lattice relaxation measurements, supported by classical molecular dynamics simulations, we are able to establish the role of water molecules in stabilizing the dispersion. We show that water molecules are localized at the Mo-terminated edges of the MoS₂ sheets, thereby inhibiting chemical erosion of the sheets, and they also exhibit enhanced interactions with the solvent NMP molecules, leading to the stability of the dispersion

Comparison of WT-1 expression and presence of proteinuria (ACR) in diabetic patients at various eGFR cutoffs.

<p>Bar graph showing percentage of patents detected with proteinuria or WT1 expression in urinary exosomes at various cutoff values of eGFR between 60–90 ml. min⁻¹/1.73 m²). WT-1 expression was detected in higher percentage of patients at earlier fall in GFR (eGFR<70/80/90 ml. min⁻¹/1.73 m²).</p

Detection of WT1 protein in urinary exosomes of diabetic patients with or without proteinuria.

<p>A) Representative immunoblots for WT1 and TSG101 proteins in urinary exosome samples from, type 1 diabetic patients with or without proteinuria and healthy controls. Exosomal protein obtained from same urine volume was loaded for all the samples. B) Frequency of WT1 expression in urinary exosomes from diabetic patients with or without proteinuria and healthy controls. All subjects were positive for TSG101 protein, an exosomal marker (data not shown). Densitometry analysis of WT1 bands in: C) Type-1 diabetic patients, using Mann-Whitney U test, and D) Proteinuria and Non-Proteinuria groups, using ANOVA rank test. The boxes indicate median and 25th and 75th percentiles; Outliers are indicated by closed dots. p<0.05 was considered significant.</p

Predicting mortality with the international classification of disease injury severity score using survival risk ratios derived from an Indian trauma population: A cohort study

<div><p>Background</p><p>Trauma is predicted to become the third leading cause of death in India by 2020, which indicate the need for urgent action. Trauma scores such as the international classification of diseases injury severity score (ICISS) have been used with great success in trauma research and in quality programmes to improve trauma care. To this date no valid trauma score has been developed for the Indian population.</p><p>Study design</p><p>This retrospective cohort study used a dataset of 16047 trauma-patients from four public university hospitals in urban India, which was divided into derivation and validation subsets. All injuries in the dataset were assigned an international classification of disease (ICD) code. Survival Risk Ratios (SRRs), for mortality within 24 hours and 30 days were then calculated for each ICD-code and used to calculate the corresponding ICISS. Score performance was measured using discrimination by calculating the area under the receiver operating characteristics curve (AUROCC) and calibration by calculating the calibration slope and intercept to plot a calibration curve.</p><p>Results</p><p>Predictions of 30-day mortality showed an AUROCC of 0.618, calibration slope of 0.269 and calibration intercept of 0.071. Estimates of 24-hour mortality consistently showed low AUROCCs and negative calibration slopes.</p><p>Conclusions</p><p>We attempted to derive and validate a version of the ICISS using SRRs calculated from an Indian population. However, the developed ICISS-scores overestimate mortality and implementing these scores in clinical or policy contexts is not recommended. This study, as well as previous reports, suggest that other scoring systems might be better suited for India and other Low- and middle-income countries until more data are available.</p></div

Comparison of renal function parameters between WT1 positive and WT1 negative diabetic subjects.

<p>Box plots comparing; A) Estimated GFR; B) Urine protein-to- creatinine ratio; C) Urine albumin-to-creatinine ratio; and D) serum Creatinine levels between WT1 positive and WT1 negative diabetic patients. The boxes indicate median and 25th and 75th percentiles; Outliers are indicated by closed dots. Data were compared by the Mann-Whitney U test. p<0.05 was considered significant.</p

Missing data per variable.

<p>Missing data per variable.</p

Calibration plots comparing observed and predicted mortality.

<p>Plots for the validation sample are shown for <b>(A)</b> within 30 days and <b>(B)</b> within 24 hours. Abbreviations: CSL: Calibration line slope, CLI: Calibration line intercept.</p

Area under the receiver operating characteristics curve (AUROCC) for ICISSm30d and ICISSm24h.

<p>Area under the receiver operating characteristics curve (AUROCC) for ICISSm30d and ICISSm24h.</p

Patient characteristics.

<p>Patient characteristics.</p