Have nanoparticles lost their stripes?

The world of materials science and nanotechnology is certainly not without controversy. Health and safety, environmental concerns, and other issues arise repeatedly especially when new substances with intriguing properties emerge. But, controversy can also arise when researchers find themselves in disagreement regarding their successes or alleged failures. One such controversy has even hit the (almost) mainstream press.

According to the Royal Society of Chemistry's flagship magazine Chemistry World, Francesco Stellacci formerly of MIT was using thiolated ligands to decorate nanoparticles, as were others at the time.
In 2004, however, his team published a paper in the journal Nature Materials in which they claimed to have shown that if they used two different thiolated ligands with gold nanoparticles, the ligands spontaneously self-assemble into alternative, discrete and evenly spaced stripes around the nanoparticle. The evidence was in their scanning tunnelling micrographs and they went on to extend their particles in various ways. Such control hinted at greater things to come for nanotechnology.

But, writing in a recent issue of the Wiley-VCH journal Small, Raphaël Lévy of the University of Liverpool explains how he was not convinced by the STM images that Stellacci's team had made stripy nanoparticles. He contends that the evenly-spaced stripes are nothing more than an artefact of the STM scanning process. Stellacci retorts in the same issue of the journal that Lévy and other detractors are mistaken and that subsequent years of work and additional evidence support the original claims. Stellacci currently at the École Polytechnique Fédérale de Lausanne in Switzerland asserts in a quote to Chemistry World that his peer-reviewed papers detailing NMR spectra, transmission electron microscopy, atomic force microscopy and X-ray crystal structures all support the stripes.

The research group of Sharon Glotzer of the University of Michigan have simulated Stellacci's nanoparticles and say their models and predictions lend further support as well as themselves having in turn been validated by experiments in the Stellacci lab. However, STM expert Philip Moriarty of the University of Nottingham, suggests that the stripes span but a few pixels in the images and could simply be noise.

Writing on his blog towards the end of 2012, Lévy points out that it took three years from submission for his critique of the 2004 Stellacci work to appear in Small, although it had six months prior to that been submitted to and presumably rejected by Nature Materials. Regardless, Lévy points out that the STM images are incompatible with a stripy hypothesis because of fundamental geometric reasons. "If stripes are regularly spaced in 3D they cannot be in a 2D projection," he says. He and his colleagues also used fast Fourier transform analysis to look at the periodicity and their evidence suggests that the stripes are imaging artefacts.

The comments on Lévy's blog range from accusations of time and money wasting to full on support. Either way debate is healthy and scientific criticism as vital now as ever. Now, Paul Jump, writing in the newspaper, Times Higher Education, reports that Lévy's critique not only provides an interesting perspective on a specific piece of research that may or may not be ultimately validated, but raises numerous questions about the current state of scientific peer review and whether or not an approach to refereeing of papers involving a blog-type commenting system might not be more appropriate for modern science.

According to a comment from Moriarty on the Jump's TLS article online, Pep Pàmies, an associated editor at Nature Materials, posted several comments on Lévy's blog in support of the decision to publish Stellacci's original paper. There are now at least a couple of dozen comments on the TLS article itself. If only there were some centralised system for pulling all the arguments together and perhaps tying them to the original papers from Stellacci and from Lévy. Perhaps we will one day see such a development in web 3.0. Meanwhile, we still don't know for sure whether those gold nanoparticles are stripy or not!

There is a coda to this ongoing saga, in that a former MIT student of Stellacci published a guest post on Lévy's blog in which he suggested that the stripes were indeed artefacts of the imaging process and that he had doubts in 2005 not a year after the original paper appeared...