Short-Wave Infrared Quantum Dots with Compact Sizes as Molecular Probes for Fluorescence Microscopy
Authors: Phuong Le
Paul R Selvin
Duncan Nall
Zhiyuan Han
Andrew M Smith
Yang Liu
Junlong Geng
Mohammad U Zahid
Yeoan Youn
Suresh Sarkar
Journal: Journal of the American Chemical Society (2020)
Discipline: CHEMISTRY
Keywords: SWIR emission; contrast agents; in vivo animal imaging; blood vessels; semiconductor quantum dots
Affiliations: Department of Bioengineering , University of Illinois at Urbana-Champaign , Urbana , Illinois 61801 , United States., Micro and Nanotechnology Laboratory , University of Illinois at Urbana-Champaign , Urbana , Illinois 61801 , United States., Beckman Institute for Advanced Science and Technology , University of Illinois at Urbana-Champaign , Urbana , Illinois 61801 , United States., Department of Materials Science and Engineering , University of Illinois at Urbana-Champaign , Urbana , Illinois 61801 , United States., Department of Physics , University of Illinois at Urbana-Champaign , Urbana , Illinois 61801 , United States., Center for the Physics of Living Cells , University of Illinois at Urbana-Champaign , Urbana , Illinois 61801 , United States., Center for Biophysics and Quantitative Biology , University of Illinois at Urbana-Champaign , Urbana , Illinois 61801 , United States., Carl R. Woese Institute for Genomic Biology , University of Illinois at Urbana-Champaign , Urbana , Illinois 61801 , United States., Carle Illinois College of Medicine , Urbana , Illinois 61801 , United States.

Abstract:  Materials with short-wave infrared (SWIR) emission are promising contrast agents for in vivo animal imaging, providing high-contrast and high-resolution images of blood vessels in deep tissues. However, SWIR emitters have not been developed as molecular labels for microscopy applications in the life sciences, which require optimized probes that are bright, stable, and small. Here, we design and synthesize semiconductor quantum dots (QDs) with SWIR emission based on HgxCd1-xSe alloy cores red shifted to the SWIR by epitaxial deposition of thin HgxCd1-xS shells with a small band gap. By tuning alloy composition alone, the emission can be shifted across the visible-to-SWIR (VIR) spectra while maintaining a small and equal size, allowing direct comparisons of molecular labeling performance across a broad range of wavelength. After coating with click-functional multidentate polymers, the VIR-QD spectral series has high quantum yield in the SWIR (14-33%), compact size (13 nm hydrodynamic diameter), and long-term stability in aqueous media during continuous excitation. We show that these properties enable diverse applications of SWIR molecular probes for fluorescence microscopy using conjugates of antibodies, growth factors, and nucleic acids. A broadly useful outcome is a 10-55-fold enhancement of the signal-to-background ratio at both the single-molecule level and the ensemble level in the SWIR relative to visible wavelengths, primarily due to drastically reduced autofluorescence. We anticipate that VIR-QDs with SWIR emission will enable ultrasensitive molecular imaging of low-copy number analytes in biospecimens with high autofluorescence. 

Retracted: No

PubPeer comments:
 *[right]* Fig 4.  Estimation of apoptotic cell population by annexin V PI staining at indicated doses of lactucopicrin. ... The results indicate that with increasing doses of the compound, the population of both early and late apoptotic cells increased significantly . Appears to be the original of *[left]* Fig 4 from [Hou et al (2020)] , though extensively re-worked. ![file] UPDATE: Another sighting! Fig 5 from [Wang et al (2018)] .  Estimation of apoptotic cell populations by annexin V PI staining of HCT-116 cells using flow cytometry...The results revealed that the apoptotic cell populations increased from 3.04% in the controls to 33.9% at 30u03bcM concentration. ![file] , 
 *[above]* Figure 5 from [Zhang et al (2018)] .  Effect of lactucopicrin on the expression of Bax and Bcl-2 expression in SKMEL-5 human skin cancer cells at indicated doses by (A) western blotting . *[below]* Figure 7A from [Gong et al (2017)] .  Effect of aesculetin on the expression levels of Bcl-2 and Bax which are apoptosis-related proteins. ![file] , 
 *[right]* Figure 3A.  Lactucopicrin-induced apoptosis in human SKMEL-5 human skin cancer cells. (A) DAPI staining at indicated concentrations. *[left]* Figure 2 from [Zeng et al (2018)] .  Induction of apoptosis by caffeic acid n-butyl ester at indicated concentrations as depicted by DAPI staining. ![file] , 
 As is the custom with this journal, the paper has undergone a stealth revision or correction to replace Figs 3, 4 and 5. The version currently provided by the journal website was created modified on 5 February 2021. ![file] Interested readers can still consult the original figures via the copies [archived at SemanticScholar] . ![file] The new Fig 4 follows a specific style of flow-cytometry scatterplot, encountered frequently within J.BUOn stealth corrections (for all manner of cell-lines) and infrequently anywhere else. ![file] ![] , 
 It gets better! The replacement Fig 4 from [Zhang et al (2018)] *[right]* and the replacement Fig 6 from [Wu Li (2017)] *[left]* are not only surprisingly similar in general appearance; one panel is **identical**. ![file] I realise that the editors primary concern is to fill what would otherwise be embarrassing gaps in each paper, left after removing figures with problematic provenance, and that the information value of these replacements is nuncupatory. Even so, they could have invested a little more effort in it. ,