Spherical Nucleic Acid


Some readers might wonder why I am going on about this, so let me tell you: this is a considerably more important story than Stripy Nanoparticles Revisited. If, as I am arguing, some of this science is shaky, then it is not only the way we evaluate scientists and spend public money which are put into question, but the foundation of ongoing clinical trials.

Back to basics: in the section of Mirkin’s group PhD dissertation (previous post) that respond to our critique of their work on Spherical Nucleic Acid / SmartFlare / StickyFlare, they wrote the following:

Additionally, since the commercialization and sale of the nanoflare platform under the trade name Smartflare (Millipore), dozens of researchers around the world have participated in successful sequence-specific gene detection.[80]

Reference [80] correspond to six (half a dozen) articles, 80a to 80f (see below for details and links). Out of these six, only two are actual research papers, and, for both, the SmartFlares are a very minor addition to the work. Out of these two, only one is completely independent of Mirkin/EMD Millipore (the other one comes from Northwestern).

80a) is not primary research; it is an advertorial produced by EMD Millipore.

80b) is not primary research: it is a 300 words congress abstract (no figure). A follow up paper by the same group is discussed here.

80c) is a review and it is a collaboration between Northwestern (Mirkin’s University) and EMD Millipore. CoI statement from the paper: “D. Weldon is the R&D Manager at EMD Millipore responsible for the production of SmartFlares. Patents related to therapeutically targeting Nodal in tumor cells have been awarded to E.A. Seftor, R.E.B. Seftor, and M.J.C. Hendrix.

80d) is a research paper. It does not show in any way that SmartFlares work. It assumes it does. The SmartFlare is a minor part of the article.

80e) is not primary research: it is an advertorial in a magazine funded by company advertising (including EMD Millipore in that very issue). The author is a journalist working for the magazine, not a practicing scientist.

80f) is a research paper. It does not show in any way that SmartFlares work. It assumes it does. SmartFlares are a very minor part of the article. The authors are from Northwestern, i.e. Mirkin’s University.


A response from Chad Mirkin’s group

Well nearly. Possibly as close as we might get.

If you have followed the Spherical Nucleic Acid / SmartFlare / StickyFlare story on this blog, you will know that we have raised doubts about the endosomal escape of these nanoparticles which are supposed to reach the cytosol of cells where they could detect mRNAs. We have even published an article on this topic. The Mirkin group has developed the technology and it has been commercialized four years ago for the live cell detection of mRNAs by EMD Millipore.

One PNAS paper on the topic was Briley et al (see here for letter to PNAS and what happened to that letter). In his PhD dissertation (Briley, W. E. (2016), William Edward Briley respond to our criticism. I reproduce the relevant section below. One might note that there is an incredibly simple way to determine the localisation of these particles inside the cells: electron microscopy, a technique which has been used for this exact purpose for over 50 years. We have used it. The results were unambiguous.

2.3 Commentary on the Endosomal Escape of SNAs
Though the endosomal escape of SNA nanostructures such as the Nanoflare and stickyflare is evident based upon their ability to provide sequence-specific information regarding RNA levels and locations within cells, one researcher has concluded that SNAs cannot escape from endosomes.[75] That researcher [That’s me!] is ignoring the many papers now that use such architectures for sequence-specific cell-sorting experiments. Indeed, if these architectures, which are taken up by scavenger-receptor mediated endosomal pathways,[68a] do not escape the endosome, then it is difficult to understand the reports by the many groups who have documented the sequencespecific function of SNAs (all of which require endosomal escape), in antisense gene regulation,[12, 44-45, 53] siRNA gene regulation,[20, 68b, 76] nanoflare gene detection,[47, 67a, 67c, 77] and sticky-flare gene detection.[78] Perhaps the best demonstration of this sequence specificity is in the function of the multiplexed Nanoflare.[67a] This nanoconjugate, discussed in chapter 1, contains two targeting sequences specific to two different genes (actin and survivin). When cells treated with multiplexed nanoflares were subjected to siRNA that specifically knocked down the expression of survivin, a corresponding decrease of fluorescence was observed in the nanoflare’s survivin-associated fluorescence (cy5), but not the actin-associated fluorescence (cy3) compared to control.[67a] Likewise, when cells were subjected to actin-targeting siRNA, a decrease in actin-associated fluorescence was observed, with no decrease of survivin-associated fluorescence.
These results indicate that the detection by nanoflares is unique to the targeted mRNA transcript. To rule out any possible effects of the fluorophores, the Cy5 and Cy3 dyes were switched to the other gene (actin-cy5, survivin-cy3), and again the corresponding sequence-specific responses were observed. Importantly, since the development of the multiplexed nanoflare, other research groups have independently developed nanoflare-like structures capable of sequence-specific detection of 3,[57] and even 4[79] genes simultaneously. Additionally, since the commercialization and sale of the nanoflare platform under the trade name Smartflare (Millipore), dozens of researchers around the world have participated in successful sequence-specific gene detection.[80]
Further evidence of SNA endosome escape can be seen visually through analysis of the sticky-flare construct. If sticky-flares were incapable of escaping endosomes, one would expect consistent colocalization with endosomes. However, this is not the case. The patterns of β-actin targeted sticky-flares, when used in HeLa cells, instead exhibit localization around mitochondria. If such structures were limited to endosomes, it is inconceivable that they would co-localize with specific organelles. This is consistent with mitochondrial localization of multiple RNAs which
has also been identified by other groups, using multiple techniques, in HeLa cells.[74] Sticky-flare release from the endosome was further confirmed by designing sticky-flares targeting a second sequence, a U1 short nuclear RNA (snRNA). U1 snRNA is known to traffic from the cytoplasm to the nucleus. Indeed, cells treated with U1-targeting sticky-flares exhibited specific fluorescence within the nucleus. The pattern observed indicates nuclear localization through endosomal escape and sequence-specific tagging of an RNA that is actively transported into the nucleus. Again, this would not be possible if such structures were confined exclusively to endosomes. Speculation that SNAs do not escape endosomes has been fueled by the observation that the fluorescence pattern of β-actin in MEFs is punctate, which has been interpreted as an indication that the sticky-flares are simply trapped in endosomes. However, β-actin is well known to exhibit punctate fluorescence in many cases, an observation made by others in multiple cell lines, including MEFs.[81] Punctate fluorescence is very common in RNA-labeling studies and well known by researchers familiar with FISH.82 This is due to the fact that RNA is often packaged into large RNA-containing granules, which facilitates transport and translational control of the included transcripts.[82b, 83] Such packaging into granules has been extensively studied using β-actin mRNA. Thus, the fact that sticky-flares targeting β-actin were packaged into granules as previously observed, while U1-targeting sticky-flares were specific to the nucleus in the same cell line, demonstrates the functionality of the construct.
Taken together, the success of the many groups who use flare architectures for the detection and knockdown of RNA in cells, and the work of dozens of labs studying related nanoparticle constructs, provide unambiguous evidence of the ability for such architectures to escape the endosome and participate in reactions exclusive to the cytosol. The mechanism of endosomal escape for nanoparticle-based vehicles is currently unknown and is an interesting and important question that is actively being investigated by many in the field.[84]


Briley, W. E. (2016). Investigation and manipulation of the local microenvironment of spherical nucleic acid nanoconjugates (Order No. 10117274). Available from ProQuest Dissertations & Theses Global. (1795522748). Retrieved from https://search.proquest.com/docview/1795522748?accountid=12117

SmartFlare controversy: independent confirmation of endosomal localization

Check this previous post for a quick summary of the SmartFlare controversy, or read all SmartFlare-related posts if you are really passionate.

At the centre of the SmartFlare controversy is the rather simple question, from an experimental point of view, of how many Spherical Nucleic Acids (to use Chad Mirkin’s terminology), if any, escape the endosomal pathway.

In contradiction with Chad Mirkin’s many peer reviewed articles and EMD Millipore marketing material, we concluded (Mason et al, 2016) that the Spherical Nucleic Acids do not escape endosomes and do not detect cytosolic mRNAs.

A few days ago, Sven Budik et al, an Austrian group published their evaluation of the SmartFlare in the context of equine embryo development. They write: “In all positive cells,
regardless of whether they occurred in equine conceptus, trophoblastic vesicle or fibroblast cell culture, the fluorescence signal showed a spotted pattern that is in accordance with the observations of Mason et al. (2016).

They also used electron microscopy to look at the intracellular localization of the particles. Here is the relevant part of their discussion and conclusion (emphasis mine):

The present study indicates that the intracellular process of nanogold particle uptake is endocytic and endosomal with a lysosomal sorting after longer incubation periods. This finding is in agreement with results from HeLa cells in vitro (Gilleron et al. 2013). Similarly, nanoparticles injected intravenously were taken up by endocytosis and later
clustered in lysosomes primarily in macrophages (Sadauskas et al. 2007). The incorporation time of lipid nanoparticlecontaining short interfering RNA gold particles in HeLa cells was similar (Gilleron et al. 2013) to that demonstrated in equine trophoblast vesicles in the present study. Accumulation of SmartFlare probes in residual bodies may be a consequence of increased stability of the immobilised oligonucleotides adjacent to the nanogold particles due to enhanced nuclease resistance (Rosi et al. 2006). In accordance with the results of Mason et al. (2016), we observed no or very few nanogold particles free in the cytoplasm, confirming a primarily endosomal and lysosomal localisation.

This observation raises the question how a specific SmartFlare probe is able to detect its target mRNA located in the cytoplasm. One possible explanation for the generation of lysosome-located specific fluorescence signals by SmartFlare probes could be the existence of specific RNA sequences imported for subsequent degradation into lysosomes (Fujiwara et al. 2013). Further studies using qRT-PCR investigating the isolated lysosomal fraction before and after incubation with specific SmartFlare probes are necessary to confirm this hypothesis. An 18S RNA nano-flare probe had a dose-dependent cytotoxic effect on porcine fetal fibroblasts (Fu et al. 2016). In contrast, no cytotoxic effects or changes in morphology after incorporation of antisense oligonucleotide nanogold particles in a mouse endothelial cell line were observed by Rosi et al. (2006). In addition, in the present study, there was no evidence that incubation with the SmartFlare probes had a toxic effect on the equine cells tested, even at higher concentrations. This is in accordance with the results of Pan et al. (2009) demonstrating that 15-nm gold particles have only low cytotoxic effects compared with the detrimental effects of small 1.4-nm gold particles.

In conclusion, SmartFlare probes pass into early equine conceptuses at stages used for embryo transfer, as well as trophoblast vesicles and cells cultured in vitro. In these early ZP equine conceptuses, the time frame (.5 and ,24 h) for SmartFlare uptake would be suitable for practical applications in commercial embryo transfer programs. Therefore, these probes are suggested to be applicable to pre-implantation genetic diagnosis before transfer of these conceptuses to the recipient.

In summary, the authors’ results are entirely consistent with our observations. They conclude, quite reasonably, that if SmartFlares detect mRNAs whilst being in endosomes, they cannot directly detect cytosolic mRNAs. This is in direct contradiction with Mirkin et al and EMD Millipore. Then, they propose that if the SmartFlares work, they maybe detect mRNAs which are in endosomes. This an interesting hypothesis that will require further study and is very different from anything published by Mirkin and EMD Millipore (the relevant reference is here). Since Budik et al do not provide any evidence that the SmartFlares actually detect mRNAs in the first place, maybe a simpler explanation is that the SmartFlares signal is unspecific and result from the probe degradation by nucleases in endosomes.

A welcome Nature Editorial

I reproduce below a comment I have left on this Nature editorial entitled “Go forth and replicate!“.

Nature Publishing Group encouragement of replications and discussions of their own published studies is a very welcome move. Seven years ago, I wrote a letter (accompanying a submission) to the Editor of Nature Materials. The last paragraph of that letter read: “The possibility of refuting existing data and theories is an important condition of progress of scientific knowledge. The high-impact publication of wrong results can have a real impact on research activities and funding priorities. There is no doubt that the series of papers revisited in this Report contribute to shape the current scientific landscape in this area of science and that their refutation will have a large impact.” [1]

The submission was “Stripy Nanoparticles Revisited” and it took three more years to publish it… in another journal; meanwhile Nature Materials continued to publish findings based on the original flawed paper [2]. The ensuing, finally public (after three years in the secret of peer review), discussions on blogs, news commentary and follow up articles were certainly very informative on the absolute necessity of changing the ways we do science to ensure a more rapid discussion of research results [3].

One of the lessons I draw from this adventure is that the traditional publishing system is, at best ill suited (e.g. Small: three years delay), or at worst (e.g. Nature Materials) completely reluctant at considering replications or challenges to their published findings. Therefore, I am now using PrePrints (e.g. to publish a letter PNAS won’t share with their readers [4]), PubPeer and journals such as ScienceOpen where publication happens immediately and peer review follows [5].

So whilst I warmly welcome this editorial, it will need a little more to convince me that it is not a complete waste of time to use the traditional channels to open discussions of published results.

[1] The rest of letter can be found at https://raphazlab.wordpress.com/2012/12/17/letter-to-naturematerials/
[2] The article was eventually published in Small (DOI:10.1002/smll.201001465

2 comments on PubPeer

); timeline: https://raphazlab.wordpress.com/2012/12/20/stripy-timeline/
[3] https://raphazlab.wordpress.com/stripy-outside/
[4] https://raphazlab.wordpress.com/2015/11/16/pnas-your-letter-does-not-contribute-significantly-to-the-discussion-of-this-paper/
[5] https://raphazlab.wordpress.com/2015/11/17/the-spherical-nucleic-acids-mrna-detection-paradox/

How many people are using the #SmartFlares? Freedom of Information request provide insights

Quick summary of previous episodes for those who have not been following the saga: Chad Mirkin’s group developed a few years ago a technology to detect mRNAs in live cells, the nano-flares. That technology is currently commercialised by Merck under the name smartflares. For a number of reasons (detailed here), I was unconvinced by the publications. We bought the smartflares, studied their uptake in cells as well as their fluorescent signal and concluded that they do not (and in fact cannot) report on mRNAs levels. We published our results as well as all of the raw data

This question – how many people are using the SmartFlares? – is interesting because surely, if a multinational company such as Merck develops, advertises and sells products, to scientists worldwide, these products have to work. As Chad Mirkin himself said today at the ACS National Meeting in Philadelphia “Ultimate measure of impact is how many people are using your technologies“.

So, we must be wrong. SmartFlares must work.

But our data say otherwise, so what is going on?

One hint is the very low number of publications using the smartflares and the fact that some of those are not independent investigations. This, however does not tell us how many groups in the world are using the smartflares.

Here is an hypothesis: maybe lots of groups worldwide are spending public money on probes that don’t work… and then don’t report the results since the probes don’t work. That hypothesis is not as far fetched as it may seem: it is called negative bias in science publishing and it is one of the causes of the reproducibility crisis.

To test this hypothesis, we would need to know how many research groups worldwide have bought the smartflares, an information that I suspected Merck was not going to volunteer. So, instead, I made Freedom of Information requests to (nearly) all UK research intensive universities (the Russell group) asking whether they had evidence of smartflare purchase orders.

Some Universities (6) declined because it would have been too much work to retrieve the information but most (14) obliged. The detailed results are available here. They show that a minimum of 76 different purchases were made between the launch of the product and June 2016. The money spent is £38k representing 0.0013% of these UK universities research income. As far as I can see, none has resulted in a publication so far.

All I can say is that these data do not falsify our hypothesis.

And if after reading this, you are still unconvinced of the need to publish negative data, check the upturnedmicroscope cartoon (warning: scene of violence).




Chad Mirkin on Nano Hype

Chad Mirkin did a Reddit AMA yesterday (h/t Neil Withers).



(highlight mine)

Of these 1800 commercial products, 1700+ are in fact a single product, the famous Spherical Nucleic Acids/SmartFlares.

More on this blog and our paper (The spherical nucleic acids mRNA detection paradox) here.

With the risk of being accused of having cynical views…

A $58M question

Nanosphere, one of the three companies founded by Chad Mirkin, has been bought today for $58M by Luminex. Is this another triumph of the Spherical Nucleic Acids?

Nanosphere was founded in 1999 by Dr. Robert Letsinger and Dr. Chad Mirkin and went public in 2007 (NASDAQ: NSPH). In 2004, MIT technology reports “a powerful but cheap nanotech tool available this year could test for everything from genetic diseases to heart-attack signs.”

Mirkin says that the Nanosphere technology is orders of magnitude more sensitive than other detection techniques, as well as fast and accurate. What’s more, the technology detects DNA or proteins directly, does not require expensive and time-consuming preparation of blood samples, and can test for multiple targets at once. “It will completely change the way the world looks at diagnostics, he says. “I’m very confident that we’re going to see a lot of new diagnostic tools come out of this.”

However, 12 years after this statement and 17 years since foundation, the company is still to make a profit. It has been able to raise and spend huge amounts of money. Not being a financial expert myself, I can’t quite work out the total, but it is probably close to ten times the value it has been sold today. An article last year, entitled “Things are not well at Nanosphere” reported that the company had “burned through $412.5 million since inception”.


The difficulties of the company, visible for all for example in the evolution of the share prices since 2007 (above), have not led to any nuance in the enthusiastic celebration of Mirkin as a genius entrepreneur leading the way in the translation of nanotechnology into healthcare. Mirkin also benefitted directly through consultancy fees from 2005 to 2013 ($100k per year 2008-2013) and a 2010 news article reports that “while profits have been elusive, Nanosphere has paid off for Mr. Mirkin, who owned 840,000 shares as of this spring, or $2.5 million worth, although the stock has sagged lately…“.

Future will tell how much an important contribution to diagnostic the Spherical Nucleic probes of Nanosphere (now Luminex) will make.

At least, for the moment, it is a better outcome than another Mirkin-founded company, NanoInk.

Update: see reporting by John Pletz from Chicago Business