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Critical assessment of the evidence for striped nanoparticles.

ABSTRACT: There is now a significant body of literature which reports that stripes form in the ligand shell of suitably functionalised Au nanoparticles. This stripe morphology has been proposed to strongly affect the physicochemical and biochemical properties of the particles. We critique the published evidence for striped nanoparticles in detail, with a particular focus on the interpretation of scanning tunnelling microscopy (STM) data (as this is the only technique which ostensibly provides direct evidence for the presence of stripes). Through a combination of an exhaustive re-analysis of the original data, in addition to new experimental measurements of a simple control sample comprising entirely unfunctionalised particles, we show that all of the STM evidence for striped nanoparticles published to date can instead be explained by a combination of well-known instrumental artefacts, or by issues with data acquisition/analysis protocols. We also critically re-examine the evidence for the presence of ligand stripes which has been claimed to have been found from transmission electron microscopy, nuclear magnetic resonance spectroscopy, small angle neutron scattering experiments, and computer simulations. Although these data can indeed be interpreted in terms of stripe formation, we show that the reported results can alternatively be explained as arising from a combination of instrumental artefacts and inadequate data analysis techniques.

SUBMITTER: Stirling J

PROVIDER: S-EPMC4234314 | biostudies-literature | 2014

REPOSITORIES: biostudies-literature

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Critical assessment of the evidence for striped nanoparticles.

Stirling Julian J Lekkas Ioannis I Sweetman Adam A Djuranovic Predrag P Guo Quanmin Q Pauw Brian B Granwehr Josef J Lévy Raphaël R Moriarty Philip P

PloS one 20141117 11

There is now a significant body of literature which reports that stripes form in the ligand shell of suitably functionalised Au nanoparticles. This stripe morphology has been proposed to strongly affect the physicochemical and biochemical properties of the particles. We critique the published evidence for striped nanoparticles in detail, with a particular focus on the interpretation of scanning tunnelling microscopy (STM) data (as this is the only technique which ostensibly provides direct evide ...[more]

PMID: 25402426

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Project description:Stirling et al., (10.1371/journal.pone.0108482) presented an analysis on some of our publications on the formation of stripe-like domains on mixed-ligand coated gold nanoparticles. The authors shed doubts on some of our results however no valid argument is provided against what we have shown since our first publication: scanning tunneling microscopy (STM) images of striped nanoparticles show stripe-like domains that are independent of imaging parameters and in particular of imaging speed. We have consistently ruled out the presence of artifacts by comparing sets of images acquired at different tip speeds, finding invariance of the stipe-like domains. Stirling and co-workers incorrectly analyzed this key control, using a different microscope and imaging conditions that do not compare to ours. We show here data proving that our approach is rigorous. Furthermore, we never solely relied on image analysis to draw our conclusions; we have always used the chemical nature of the particles to assess the veracity of our images. Stirling et al. do not provide any justification for the spacing of the features that we find on nanoparticles: ~1 nm for mixed ligand particles and ~ 0.5 nm for homoligand particles. Hence our two central arguments remain unmodified: independence from imaging parameters and dependence on ligand shell chemical composition. The paper report observations on our STM images; none is a sufficient condition to prove that our images are artifacts. We thoroughly addressed issues related to STM artifacts throughout our microscopy work. Stirling et al. provide guidelines for what they consider good STM images of nanoparticles, such images are indeed present in our literature. They conclude that the evidences we provided to date are insufficient, this is a departure from one of the authors' previous article which concluded that our images were composed of artifacts. Given that four independent laboratories have reproduced our measurements and that no scientifically rigorous argument is presented to invalidate our STM images, and also given that Stirling et al. do not contest the quality of our recent STM images, we re-affirm that specific binary mixture of ligands spontaneously form features in their ligand shell that we describe as stripe-like domains ~1 nm in width.

Project description:Cigarettes with lower machine measured "tar" and nicotine yields have been marketed as "safer" than high tar products over the last four decades, but there is conflicting evidence about the impact of these products on the disease burden caused by smoking. This paper critically examines the epidemiological evidence relevant to the health consequences of "reduced yield" cigarettes. Some epidemiological studies have found attenuated risk of lung cancer but not other diseases, among people who smoke "reduced yield" cigarettes compared to smokers of unfiltered, high yield products. These studies probably overestimate the magnitude of any association with lung cancer by over adjusting for the number of cigarettes smoked per day (one aspect of compensatory smoking), and by not fully considering other differences between smokers of "high yield" and "low yield" cigarettes. Selected cohort studies in the USA and UK show that lung cancer risk continued to increase among older smokers from the 1950s to the 1980s, despite the widespread adoption of lower yield cigarettes. The change to filter tip products did not prevent a progressive increase in lung cancer risk among male smokers who began smoking during and after the second world war compared to the first world war era smokers. National trends in vital statistics data show declining lung cancer death rates in young adults, especially males, in many countries, but the extent to which this is attributable to "reduced yield" cigarettes remains unclear. No studies have adequately assessed whether health claims used to market "reduced yield" cigarettes delay cessation among smokers who might otherwise quit, or increase initiation among non-smokers. There is no convincing evidence that past changes in cigarette design have resulted in an important health benefit to either smokers or the whole population. Tobacco control policies should not allow changes in cigarette design to subvert or distract from interventions proven to reduce the prevalence, intensity, and duration of smoking.

Project description:BackgroundMental Rehearsal (MR) the cognitive act of simulating a task in our heads to pre-experience events imaginatively. It has been used widely to improve individual and collective performance in fields outside healthcare and offers potential for more efficient training in time pressured surgical and medical team contexts. The study aims to review the current systematic review literature to determine the impact of MP on surgical performance and learning.MethodsMedline, Embase, British Educational Index, CINAHL, Web of Science PsycINFO, Cochrane databased were searched in the period 1994-2018. The primary outcomes measure were performance improvements in surgical technical skills, stress reduction, confidence and team performance. Study quality of the Systematic Reviews was assessed using AMSTAR 2, a critical appraisal tool for systematic reviews. The reported impacts of MP in all included studies were mapped onto Kirkpatrick's framework for the evaluation of educational interventions.ResultsSix Systematic reviews were identified which met the inclusion criteria, of which all reported positive and varying benefits of MP on surgical performance, confidence, and coping strategies. However, reported impacts on a modified Kirkpatrick's framework did not exceed level 3. Mental practice was described in terms of mental imagery and mental rehearsal with most authors using each of the terms in their search strategies. The impacts on transfer to practice and the long- term acquisition of skills, but also personal uptake of mental practice routines were not reported.ConclusionThe majority of studies demonstrate benefits of MP for technical performance. Overall the systematic reviews were of medium to high quality. However, studies lacked a sufficiently articulated evaluation methodology to examine impacts beyond the immediate experimentations. This is also due to the limitations found in the primary studies. Future research should look at longitudinal mixed method evaluation designs and focus on real clinical teams.

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Critical assessment of the evidence for striped nanoparticles.

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Critical assessment of the evidence for striped nanoparticles.

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