This is a guest post by Mathias Brust, Professor of Chemistry at the University of Liverpool
Followers of Raphaël Lévy’s blog on “stripy nanoparticles” have been waiting eagerly for the outcome of an experimental study conducted by independent experts to evaluate the veracity of Stellacci’s et al. original interpretation of their STM data as the presence of molecular stripes in certain thiolate-capped gold nanoparticles.
I assume that the two papers recently published in ACS Nano and Langmuir, respectively, both co-authored by recognized STM experts, detail the various findings of this study. Unfortunately, the authors shy away from making clear statements in relation to Stellacci’s previous work, published most prominently in 2004 in Nature Materials. The new images obtained with state of the art modern equipment, unlike the original ones from 2004, show hardly any discernible features. Indeed, in the absence of Stellacci’s previous claims, nobody would see anything special in these new data, which just look like rather well done STM images of gold nanoparticles, with some inevitable noise. Unfortunately, rather than stating that there is a clear discrepancy between the original data from 2004 and the new ones, the authors employ an arsenal of image analysis techniques to convince presumably themselves and evidently the referees that the now barely discernible ripples at the noise level represent indeed all the features Stellacci et al. had previously reported in much clearer images obtained with inferior instrumentation and without sophisticated image analysis. The new study thus implicitly admits interpretation errors in the original work, while explicitly aiming to corroborate it. A tacit assertion that it is hard to do these experiments, which are prone to imaging artifacts, is perhaps the only hint that maybe before we were not looking at the real thing at all. I strongly advise everybody interested in this debate to look at the newly published images, and again at the ones from 2004, to make up their own mind on this topic. I suspect that an even more carefully conducted study in the future may reveal that the particles have no discernible features at the molecular level and that the stripes are “invisible” by STM. A new class of “stealth stripes” would make a nice cover for Nature Materials.