The recipe for "Cube-shaped nitrogen-doped carbon dots" is easier and lower-tech than one might imagine:
*0.5 g of the calcein dye was dissolved in distilled water (20.0 mL) and kept in domestic microwave oven (power intensity = 600 W) for 30 min. After that the solution was placed for hydrothermal reaction in Teflon lined stainless steel autoclave at 150° C for 2 h. *
These CCDs are impressively consistent in terms of size and appearance. "Figure 1. (C) TEM image of CCDs."
The many desirable properties of these CCDs include bacteriotoxicity, once they have bound Pb2+. "Figure 7. Confocal microscopic images of MCF-7 and E. coli cells, before and after incubation with fixed Pb2+, captured at different time intervals: (A and E) 0, (B and F) 10, (C and G) 20, (D and H) 30 s, respectively. Confocal microscopic images of MCF-7 cells, after incubation with different concentrations of Pb2+: (I) 0, (J) 1.0, (K) 2.0, and (L) 5.0 μg L−1."
I have to say that panels (I) to (L), purportedly showing different cultures of cancer cells incubated with different concentrations of bound Pb2+, appear to be all the same image. There are also resemblances to panels (A) to (D), which for convenience I have rotated through 180 deg. and repeated as a fourth row below (I) to (L).
Comparisons are also possible between panels (E) to (H) -- E. coli cultures, incubated with fixed Pb2+ for 0, 10, 20, 30 seconds -- with Figure 6 from Roy et al (2015) https://pubpeer.com/publications/420FF5968F52006E6E80CAE776F8CC
Except Fig. 6 depicts "Confocal images of live (green) and dead (red) E. coli bacterial cells: (A) without F-AgNPs, (B) after 5 min, (C) 15 min and (D) 30 min incubation with F-AgNPs."
"Figure 2. (a) XPS spectrum of CCDs. Deconvoluted (b) C 1s, (c) N 1s, and (d) O 1s XPS spectra of CCDs."
The scatter of experimental points in Fig 2C -- used to fit a combination of four functions -- appears in other papers, used to fit different functions each time. See Choundary et al (2017) https://pubpeer.com/publications/488D59B462B4FBAEB4AEBA2190E265#2
Karfa et al (2016) https://pubpeer.com/publications/05C01FDC20C60489EE35CF3FEAAD90#6
Patra et al (2016) https://pubpeer.com/publications/C64749A8DE4EE82F4CE90AB6386BF9#5
All 10 known appearances of the Dromedary Distribution brought together here: https://pubpeer.com/publications/488D59B462B4FBAEB4AEBA2190E265#8
"Figure 1. … (F) Zeta potential plot of CCDs"
Other versions of the same function are brought together at Patra et al. (2016), https://pubpeer.com/publications/48D0BA291B328B05395A6E21D8A8B9#8
including "Figure S5: … Zeta potential plot" from Choudary et al. (2017), https://pubpeer.com/publications/02C5FAC82721C30D2E819FDC7AEF10
"Figure S4: Zeta potential plot of the prepared CDs" from Patra et al. (2016) https://pubpeer.com/publications/80BA2E5AAFD159C5E6CCFEADB7B2F1
#1 In addition to an improbable level of size and shape consistency, the TEM image in Fig 1C also shows clear light edges where the shapes overlap. As these are regions of even greater "carbon dot" density, these overlaps should appear darker by TEM, yet instead there is clear outline every time overlap occurs:
Figure 1C continued..... Next, in addition to the regularity of size and shape of these "carbon dots", there is evidence that the pattern of squares in Figure 1C is repeated several times within. You can even enhance the brightness and contrast manually (which I did using ppt) and pick out the appearance of a comparatively darker square, which then provides a convenient point-of-reference to view this clearly. Doing so also indicates that the bottom right region are the same set of squares rotated.
Figure 6D, the cytotoxicity data (including error bars) are identical for 24 and 48 h incubation times:
And these results also appear to be the same as used for Figure 6G in Patra et al., J Mater Chem C (where again 24 and 48 are identical).
https://pubpeer.com/publications/80BA2E5AAFD159C5E6CCFEADB7B2F1#14
"As shown in the Table (S1), the effect of microwave treatment is very prominent and observable." Do the authors have any actual data to back up the "shape" results in this table, i.e. confirming their successful synthetic strategy to influence shape (which you would think is needed to support the claims made within the manuscript), as the only TEM "results" presented are for their cubed particles in Fig 1C? No doubt many readers would find it fascinating to see these additional TEM results generated by the authors to describe these "very prominent and observable" results for the other shapes presented within Table S1:
I also am a bit confused by their chemical scheme, which shows Pb2+ binding to, well, what exactly? They have just re-drawn the same molecule in a different colour surrounded by "Pb2+" circles. Why would Pb2+ associate in this way but not the other ions out of curiosity, since no binding mode whatsoever is indicated?
I also am a bit confused by their chemical scheme, which shows Pb2+ binding to, well, what exactly?
That pentagonal structure in Scheme 1 does not strike me as entirely plausible. The text does not explain its origins... it appears to crystallise spontaneously around each cubic carbon dot (these being somehow small enough to fit into the central void of the pentagonal ring), as a way of binding to Pb++ ions.
In lieu of these useful details, the authors do provide us with "Figure 3. Different calligraphy patterns drawn by sketch pen filled with CCD solution under UV light (λ = 360 nm)".
I have to say that panels (I) to (L), purportedly showing different cultures of cancer cells incubated with different concentrations of bound Pb2+, appear to be all the same image. There are also resemblances to panels (A) to (D), which for convenience I have rotated through 180 deg. and repeated as a fourth row below (I) to (L).
Close-ups of panels (A)-(D) / (I)-(L) of Figure 7 appear in Figures 5 and 6 of Roy et al. (2017), with different descriptions. https://pubpeer.com/publications/33CB940D42723BAB8B4F737B434E86#3
And in many other publications from the same team, although characterised differently in each appearance.
#12 Their proposed chemical structure appears to be a new (?) cyclic calcein derivative, yet no chemical characterisation data (nmr, mass spec etc) is provided. The only data is xps showing the presence of C, N, and O in the whole carbon dot. It is quite a leap from this finding to their confident description of a specific - and rather complex - chemical structure in the Scheme. As you would think this has a big influence on Pb2+ binding - I.e. the basis for the whole manuscript - I am amazed such fundamental scientific information has been omitted in favour of such delightful doodling.
Retracted Mary 30th. "The Editor retracts this article (10.1021/acssuschemeng.6b01463) based on the duplication of images from DOI 10.1016/j.cej.2016.11.122 that were presented as different materials."
Six months from initiation of peer post-review to retraction is exemplary alacrity by current standards, and ACS is to be commended. It is understandable that the retraction cites a clear and demonstrable violation of editorial policy and does not get into discussion of fabrications that may be obvious, but cannot be definitively traced to the authors. This is an especially good tactic with authors that have already threatened critical peers with legal action, although they have not deigned to reply to any of the comments offered here.
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