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Shortwave infrared polymethine fluorophores matched to excitation lasers enable non-invasive, multicolour in vivo imaging in real time

Abstract

High-resolution, multiplexed experiments are a staple in cellular imaging. Analogous experiments in animals are challenging, however, due to substantial scattering and autofluorescence in tissue at visible (350–700 nm) and near-infrared (700–1,000 nm) wavelengths. Here, we enable real-time, non-invasive multicolour imaging experiments in animals through the design of optical contrast agents for the shortwave infrared (SWIR, 1,000–2,000 nm) region and complementary advances in imaging technologies. We developed tunable, SWIR-emissive flavylium polymethine dyes and established relationships between structure and photophysical properties for this class of bright SWIR contrast agents. In parallel, we designed an imaging system with variable near-infrared/SWIR excitation and single-channel detection, facilitating video-rate multicolour SWIR imaging for optically guided surgery and imaging of awake and moving mice with multiplexed detection. Optimized dyes matched to 980 nm and 1,064 nm lasers, combined with the clinically approved indocyanine green, enabled real-time, three-colour imaging with high temporal and spatial resolutions.

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Fig. 1: Real-time excitation-multiplexed SWIR imaging design.
Fig. 2: Panel of flavylium heptamethine dyes and their photophysical properties.
Fig. 3: Excitation-multiplexed SWIR imaging.
Fig. 4: Applications enhanced by SWIR multiplexed imaging.
Fig. 5: Orthogonal lymphatic and circulatory imaging with high spatiotemporal resolution after intradermal (i.d.) injection of ICG and i.v. injection of JuloFlav7 (3) micelles.

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Data availability

Image datasets, including all raw and processed imaging data generated in this work, are available at BioImage Archive (accession number: S-BIAD27). All other datasets that support the findings of this study are contained within the manuscript and its Supplementary Information.

Code availability

Custom computer programs used for the work are available at GitHub (https://gitlab.com/brunslab/ccda).

References

  1. Dean, K. M. & Palmer, A. E. Advances in fluorescence labeling strategies for dynamic cellular imaging. Nat. Chem. Biol. 10, 512–523 (2014).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  2. Wei, L. et al. Super-multiplex vibrational imaging. Nature 544, 465–470 (2017).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  3. Frangioni, J. V. In vivo near-infrared fluorescence imaging. Curr. Opin. Chem. Biol. 7, 626–634 (2003).

    Article  CAS  PubMed  Google Scholar 

  4. Kong, L. et al. Continuous volumetric imaging via an optical phase-locked ultrasound lens. Nat. Methods 12, 759–762 (2015).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  5. Grimm, J. B. et al. A general method to fine-tune fluorophores for live-cell and in vivo imaging. Nat. Methods 14, 987–994 (2017).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  6. Fenrich, K. K. et al. Long-term in vivo imaging of normal and pathological mouse spinal cord with subcellular resolution using implanted glass windows. J. Physiol. 590, 3665–3675 (2012).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  7. Rakhymzhan, A. et al. Synergistic strategy for multicolor two-photon microscopy: application to the analysis of germinal center reactions in vivo. Sci. Rep. 7, 7101 (2017).

    Article  PubMed  PubMed Central  CAS  Google Scholar 

  8. Kim, P., Puoris’haag, M., Côté, D., Lin, C. P. & Yun, S. H. In vivo confocal and multiphoton microendoscopy. J. Biomed. Opt. 13, 010501 (2008).

    Article  PubMed  Google Scholar 

  9. Kosaka, N., Ogawa, M., Sato, N., Choyke, P. L. & Kobayashi, H. In vivo real-time, multicolor, quantum dot lymphatic imaging. J. Invest. Dermatol. 129, 2818–2822 (2009).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  10. Erogbogbo, F. et al. In vivo targeted cancer imaging, sentinel lymph node mapping and multi-channel imaging with biocompatible silicon nanocrystals. ACS Nano 5, 413–423 (2011).

    Article  CAS  PubMed  Google Scholar 

  11. Shcherbakova, D. M. & Verkhusha, V. V. Near-infrared fluorescent proteins for multicolor in vivo imaging. Nat. Methods 10, 751–754 (2013).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  12. Zavaleta, C. L. et al. Multiplexed imaging of surface enhanced Raman scattering nanotags in living mice using noninvasive Raman spectroscopy. Proc. Natl Acad. Sci. USA 106, 13511–13516 (2009).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  13. Zhang, H. et al. Penetration depth of photons in biological tissues from hyperspectral imaging in shortwave infrared in transmission and reflection geometries. J. Biomed. Opt. 21, 126006 (2016).

    Article  PubMed  PubMed Central  Google Scholar 

  14. Carr, J. A. et al. Absorption by water increases fluorescence image contrast of biological tissue in the shortwave infrared. Proc. Natl Acad. Sci. USA 115, 9080–9085 (2018).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  15. Naczynski, D. J. et al. Rare-earth-doped biological composites as in vivo shortwave infrared reporters. Nat. Commun. 4, 2199 (2013).

    Article  CAS  PubMed  Google Scholar 

  16. Welsher, K. et al. A route to brightly fluorescent carbon nanotubes for near-infrared imaging in mice. Nat. Nanotechnol. 4, 773–780 (2009).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  17. Hong, G. et al. In vivo fluorescence imaging with Ag2S quantum dots in the second near-infrared region. Angew. Chem. Int. Ed. 51, 9818–9821 (2012).

    Article  CAS  Google Scholar 

  18. Bruns, O. T. et al. Next-generation in vivo optical imaging with short-wave infrared quantum dots. Nat. Biomed. Eng. 1, 0056 (2017).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  19. Tao, Z. et al. Biological imaging using nanoparticles of small organic molecules with fluorescence emission at wavelengths longer than 1000 nm. Angew. Chem. Int. Ed. 52, 13002–13006 (2013).

    Article  CAS  Google Scholar 

  20. Yang, Q. et al. Rational design of molecular fluorophores for biological imaging in the NIR-II window. Adv. Mater. 29, 1605497 (2017).

    Article  CAS  Google Scholar 

  21. Zhu, S. et al. 3D NIR-II molecular imaging distinguishes targeted organs with high-performance NIR-II bioconjugates. Adv. Mater. 30, 1705799 (2018).

    Article  CAS  Google Scholar 

  22. Wan, H. et al. A bright organic NIR-II nanofluorophore for three-dimensional imaging into biological tissues. Nat. Commun. 9, 1171 (2018).

    Article  PubMed  PubMed Central  CAS  Google Scholar 

  23. Wang, F. et al. Light-sheet microscopy in the near-infrared II window. Nat. Methods 16, 545–552 (2019).

    Article  PubMed  PubMed Central  CAS  Google Scholar 

  24. Zhu, S. et al. Molecular imaging of biological systems with a clickable dye in the broad 800- to 1,700-nm near-infrared window. Proc. Natl Acad. Sci. USA 114, 962–967 (2017).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  25. Ma, B. L., Zhai, X., Du, G. & Zhou, J. Orthogonal shortwave infrared emission based on rare earth nanoparticles for interference-free logical codes and bio-imaging. Chem. Sci. 10, 3281–3288 (2019).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  26. Hong, G. et al. Through-skull fluorescence imaging of the brain in a new near-infrared window. Nat. Photonics 8, 723–730 (2014).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  27. Diao, S. et al. Fluorescence imaging in vivo at wavelengths beyond 1500 nm. Angew. Chem. Int. Ed. 54, 14758–14762 (2015).

    Article  CAS  Google Scholar 

  28. Kapanidis, A. N. et al. Alternating-laser excitation of single molecules. Acc. Chem. Res. 38, 523–533 (2005).

    Article  CAS  PubMed  Google Scholar 

  29. Müller, B. K., Zaychikov, E., Bräuchle, C. & Lamb, D. C. Pulsed interleaved excitation. Biophys. J. 89, 3508–3522 (2005).

    Article  PubMed  PubMed Central  CAS  Google Scholar 

  30. Lewis, E. K. et al. Color-blind fluorescence detection for four-color DNA sequencing. Proc. Natl Acad. Sci. USA 102, 5346–5351 (2005).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  31. Garbacik, E. T., Sanz-Paz, M., Borgman, K. J. E., Campelo, F. & Garcia-Parajo, M. F. Frequency-encoded multicolor fluorescence imaging with single-photon-counting color-blind detection. Biophys. J. 115, 725–736 (2018).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  32. Gómez-García, P. A., Garbacik, E. T., Otterstrom, J. J., Garcia-Parajo, M. F. & Lakadamyali, M. Excitation-multiplexed multicolor superresolution imaging with fm-STORM and fm-DNA-PAINT. Proc. Natl Acad. Sci. USA 115, 12991–12996 (2018).

    Article  PubMed  CAS  PubMed Central  Google Scholar 

  33. Thimsen, E., Sadtler, B. & Berezin, M. Y. Shortwave-infrared (SWIR) emitters for biological imaging: a review of challenges and opportunities. Nanophotonics 6, 1043–1054 (2017).

    Article  CAS  Google Scholar 

  34. Bricks, J. L., Kachkovskii, A. D., Slominskii, Y. L., Gerasov, A. O. & Popov, S. V. Molecular design of near infrared polymethine dyes: a review. Dyes Pigm. 121, 238–255 (2015).

    Article  CAS  Google Scholar 

  35. Marshall, M. V. et al. Near-infrared fluorescence imaging in humans with indocyanine green: a review and update. Open Surg. Oncol. J. 2, 12–25 (2010).

    PubMed  PubMed Central  Google Scholar 

  36. Rurack, K. & Spieles, M. Fluorescence quantum yields of a series of red and near-infrared dyes emitting at 600–1000 nm. Anal. Chem. 83, 1232–1242 (2011).

    Article  CAS  PubMed  Google Scholar 

  37. Carr, J. A. et al. Shortwave infrared fluorescence imaging with the clinically approved near-infrared dye indocyanine green. Proc. Natl Acad. Sci. USA 115, 4465–4470 (2018).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  38. Starosolski, Z. et al. Indocyanine green fluorescence in second near-infrared (NIR-II) window. PLOS One 12, e0187563 (2017).

    Article  PubMed  PubMed Central  CAS  Google Scholar 

  39. Cosco, E. D. et al. Flavylium polymethine fluorophores for near- and shortwave infrared imaging. Angew. Chem. Int. Ed. 56, 13126–13129 (2017).

    Article  CAS  Google Scholar 

  40. Henary, M., Mojzych, M., Say, M. & Strekowski, L. Functionalization of benzo[c,d]indole system for the synthesis of visible and near-infrared dyes. J. Heterocycl. Chem. 46, 84–87 (2009).

    Article  CAS  Google Scholar 

  41. Li, B., Lu, L., Zhao, M., Lei, Z. & Zhang, F. An efficient 1064 nm NIR-II excitation fluorescent molecular dye for deep-tissue high-resolution dynamic bioimaging. Angew. Chem. Int. Ed. 57, 7483–7487 (2018).

    Article  CAS  Google Scholar 

  42. Ding, B. et al. Polymethine thiopyrylium fluorophores with absorption beyond 1000 nm for biological imaging in the second near-infrared subwindow. J. Med. Chem. 62, 2049–2059 (2019).

    Article  CAS  PubMed  Google Scholar 

  43. Wang, S. et al. Anti-quenching NIR-II molecular fluorophores for in vivo high-contrast imaging and pH sensing. Nat. Commun. 10, 1058 (2019).

    Article  PubMed  PubMed Central  CAS  Google Scholar 

  44. Lei, Z. et al. Stable, wavelength-tunable fluorescent dyes in the NIR-II region for in vivo high-contrast bioimaging and multiplexed biosensing. Angew. Chem. Int. Ed. 58, 8166–8171 (2019).

    Article  CAS  Google Scholar 

  45. Chen, J.-R., Wong, J.-B., Kuo, P.-Y. & Yang, D.-Y. Synthesis and characterization of coumarin-based spiropyran photochromic colorants. Org. Lett. 10, 4823–4826 (2008).

    Article  CAS  PubMed  Google Scholar 

  46. Roehri-Stoeckel, C., Gonzalez, E. & Fougerousse, A. Synthetic dyes: simple and original ways to 4-substituted flavylium salts and their corresponding vitisin derivatives. Can. J. Chem. 79, 1173–1178 (2001).

    Article  CAS  Google Scholar 

  47. Seijas, J. A., Vázquez-Tato, M. P. & Carballido-Reboredo, R. Solvent-free synthesis of functionalized flavones under microwave irradiation. J. Org. Chem. 70, 2855–2858 (2005).

    Article  CAS  PubMed  Google Scholar 

  48. Kónya, K., Pajtás, D., Kiss-Szikszai, A. & Patonay, T. Buchwald-Hartwig reactions of monohaloflavones. Eur. J. Org. Chem. 2015, 828–839 (2015).

    Article  CAS  Google Scholar 

  49. Kopainsky, B., Qiu, P., Kaiser, W., Sens, B. & Drexhage, K. H. Lifetime, photostability, and chemical structure of IR heptamethine cyanine dyes absorbing beyond 1 μm. Appl. Phys. B 29, 15–18 (1982).

    Article  Google Scholar 

  50. Hansch, C., Leo, A. & Taft, R. W. A survey of Hammett substituent constants and resonance and field parameters. Chem. Rev. 91, 165–195 (1991).

    Article  CAS  Google Scholar 

  51. Semonin, O. E. et al. Absolute photoluminescence quantum yields of IR-26 Dye, PbS, and PbSe quantum dots. J. Phys. Chem. Lett. 1, 2445–2450 (2010).

    Article  CAS  Google Scholar 

  52. Hatami, S. et al. Absolute photoluminescence quantum yields of IR26 and IR-emissive Cd1−xHgxTe and PbS quantum dots – method- and material-inherent challenges. Nanoscale 7, 133–143 (2015).

    Article  CAS  PubMed  Google Scholar 

  53. Lukasik, V. M. & Gillies, R. J. Animal anaesthesia for in vivo magnetic resonance. NMR Biomed. 16, 459–467 (2003).

    Article  CAS  PubMed  Google Scholar 

  54. Schwenke, D. O., Pearson, J. T., Mori, H. & Shirai, M. Long-term monitoring of pulmonary arterial pressure in conscious, unrestrained mice. J. Pharmacol. Toxicol. Methods 53, 277–283 (2006).

    Article  CAS  PubMed  Google Scholar 

  55. Sato, M. et al. Simultaneous monitoring of mouse respiratory and cardiac rates through a single precordial electrode. J. Pharmacol. Sci. 137, 177–186 (2018).

    Article  CAS  PubMed  Google Scholar 

  56. Ceppi, L. et al. Real-time single-walled carbon nanotube-based fluorescence imaging improves survival after debulking surgery in an ovarian cancer model. ACS Nano 13, 5356–5365 (2019).

    Article  CAS  PubMed  Google Scholar 

  57. Zhu, S., Tian, R., Antaris, A. L., Chen, X. & Dai, H. Near‐infrared‐II molecular dyes for cancer imaging and surgery. Adv. Mater. 31, e1900321 (2019).

    Article  PubMed  PubMed Central  CAS  Google Scholar 

  58. Cousins, A., Thompson, S. K., Wedding, A. B. & Thierry, B. Clinical relevance of novel imaging technologies for sentinel lymph node identification and staging. Biotechnol. Adv. 32, 269–279 (2014).

    Article  PubMed  Google Scholar 

  59. Rasmussen, J. C., Fife, C. E. & Sevick-Muraca, E. M. Near-infrared fluorescence lymphatic imaging in lymphangiomatosis. Lymphat. Res. Biol. 13, 195–201 (2015).

    Article  PubMed  PubMed Central  Google Scholar 

  60. Tozzi, M., Boni, L., Soldini, G., Franchin, M. & Piffaretti, G. Vascular fluorescence imaging control for complex renal artery aneurysm repair using laparoscopic nephrectomy and autotransplantation. Case Rep. Transplant. 2014, 563408 (2014).

    PubMed  PubMed Central  Google Scholar 

  61. Bexrud, J. A., Eisenberger, P., Leitch, D. C., Payne, P. R. & Schafer, L. L. Selective C-H activation α to primary amines. Bridging metallaaziridines for catalytic, intramolecular α-alkylation. J. Am. Chem. Soc. 131, 2116–2118 (2009).

    Article  CAS  PubMed  Google Scholar 

  62. Kövér, J. & Antus, S. Facile deoxygenation of hydroxylated flavonoids by palladium-catalysed reduction of its triflate derivatives. Z. Naturforsch. 60b, 792–796 (2005).

    Article  Google Scholar 

  63. Schindelin, J. et al. Fiji: an open-source platform for biological-image analysis. Nat. Methods 9, 676–682 (2012).

    Article  CAS  PubMed  Google Scholar 

  64. Rueden, C. T. et al. ImageJ2: ImageJ for the next generation of scientific image data. BMC Bioinf. 18, 529 (2017).

    Article  Google Scholar 

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Acknowledgements

This work was supported by grants to E.D.C. (NSF GRFP DGE-1144087, Christopher S. Foote Fellowship), O.T.B. (Emmy-Noether-Programme of DFG BR 5355/2-1, Helmholtz Pioneer Campus Institute for Biomedical Engineering), E.M.S. (UCLA, Sloan Research Award FG-2018-10855, NIH 1R01EB027172-01) and Helmholtz Zentrum München, and by shared instrumentation grants from the NSF (CHE-1048804) and NIH (1S10OD016387-01). We thank T. Schwarz-Romond, T. S. Bischof, D. Bengel (Helmholtz Zentrum München), K. N. Houk, J. R. Caram (UCLA) and L. D. Lavis (Janelia) for discussions and support and the Garcia-Garibay Group (UCLA) for instrumentation.

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Authors and Affiliations

Authors

Contributions

E.D.C., E.M.S. and O.T.B. designed the study. E.M.S. and O.T.B. jointly advised the study. E.D.C., A.L.S., M.P. and R.R.M. performed the synthesis. E.D.C. measured and analysed the photophysics. S.R. developed the software and built electronics and instrumentation. E.D.C., J.G.P.L. and M.W. built optical configurations. E.D.C., M.S., B.A.A. and S.G. performed imaging experiments. E.D.C., J.G.P.L. and B.A.A. analysed images. K.C.Y.W. performed cell culture experiments. E.D.C., E.M.S. and O.T.B. wrote and edited the paper. E.M.S., O.T.B. and V.N. provided funding. All authors have given approval to the final version of the manuscript. Correspondence and requests for materials should be addressed to E.M.S and O.T.B.

Corresponding authors

Correspondence to Oliver T. Bruns or Ellen M. Sletten.

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Competing interests

Material presented in this work is included in patent and patent applications US20200140404, EP3634397 and WO2018226720 with authors E.M.S and E.D.C. and PCT/EP2020065753 with authors O.T.B., E.D.C., J.G.P.L., M.W., S.R., M.S. and E.M.S.

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Extended data

Extended Data Fig. 1 Retrosynthesis of 7-aminoflavylium heterocycles.

The 7-amino-4-methyl flavylium heterocycles were accessed through flavone intermediates 13. Three routes were used to obtain flavones 13, Mentzer pyrone synthesis, Buchwald-Hartwig coupling, and acylation. Conditions and yields for each derivative can be found in the listed Supplementary Tables.

Extended Data Fig. 2 Resolution effects upon excitation multiplexing and single-channel detection in the SWIR.

a, Images of a mouse phantom acquired after injection of JuloFlav7 (3) (94 nmol) and immediate euthanasia. Images were acquired with 785 nm excitation (93 mWcm−2), 980 nm (30 mWcm−2), and 1,064 nm (11 mWcm−2) and collection 1,150–1,700 nm (48 ms, 20 fps). Displayed images are averaged over 200 frames. b, To observe resolution, 12 cross-sections were drawn over different vessels (labelled in a) and the baseline subtracted and normalized cross-sections are overlaid. ex. = excitation; LP = longpass.

Extended Data Fig. 3 Resolution effects observed upon emission multiplexing with a single excitation wavelength in the SWIR.

a, Images of a mouse phantom acquired after injection of JuloFlav7 (3) (94 nmol) and immediate euthanasia, after one freeze-thaw cycle. Images were acquired with 980 nm excitation. Laser powers and exposure time are as follows (1) 1,000 nm LP = 8.1 mWcm−2, 30 ms; 1,300 nm LP = 24 mWcm−2, 500 ms; 1,500 nm LP = 177 mWcm−2, 500 ms. Displayed images are averaged over 200 frames. b, To observe resolution, 5 cross-sections were drawn over different vessels (labelled in a) and the baseline subtracted and normalized cross-sections are overlaid. LP = longpass.

Extended Data Fig. 4 Imaging with 1064 nm excitation after injection of JuloFlav7 (3) micelles.

a, Whole mouse imaging at selected time-points after i.v. injection of JuloFlav7 (3) micelles (44 nmol) in PBS buffer with excitation at 1,064 nm (103 mWcm−1) and 1,150–1,700 nm collection (8 ms exposure time, 100 fps). b, Imaging of the mouse hind-limb at selected time points after i.v. injection of JuloFlav7 (3) micelles (55 nmol) with excitation at 1,064 nm (95 mWcm−1) with 1,100–17,00 nm collection (9 ms exposure time, 100 fps). Displayed images are averaged over 5 frames. Scale bars represent 1 cm. Data are representative of two replicate experiments.

Supplementary information

Supplementary Information

Abbreviations, Supplementary Tables 1–5, Figs. 1–16, List of Supplementary Videos 1–6, figure experimental procedures, extended data and supplementary figure experimental procedures, Notes 1–5, synthetic procedures and compound characterization.

Reporting Summary

Supplementary Video 1

Single-channel in vivo imaging with excitation 1,064 nm at 100 fps. Image sequence was frame averaged by a factor of three to reduce file size and is displayed in real time.

Supplementary Video 2

Video-rate multiplexed imaging in vivo of JuloFlav7 injection. Image sequence was frame averaged by a factor of three to reduce file size and is displayed at three times the speed.

Supplementary Video 3

Video-rate multiplexed imaging in vivo of ICG injection. Image sequence was frame averaged by a factor of three to reduce file size and is displayed at three times the speed.

Supplementary Video 4

Imaging of an awake mouse in three colours. Image sequence was not frame averaged and is displayed in real time.

Supplementary Video 5

Orthogonal circulatory and lymphatic imaging. Image sequence was frame averaged by a factor of two to reduce file size and is displayed at three times the speed.

Supplementary Video 6

Two-colour demonstration of image-guided necropsy. Image sequence was frame averaged by a factor of eight to reduce file size and is displayed at five times the speed.

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Cosco, E.D., Spearman, A.L., Ramakrishnan, S. et al. Shortwave infrared polymethine fluorophores matched to excitation lasers enable non-invasive, multicolour in vivo imaging in real time. Nat. Chem. 12, 1123–1130 (2020). https://doi.org/10.1038/s41557-020-00554-5

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