Theranostics 2019; 9(10):2856-2867. doi:10.7150/thno.33595 This issue

Research Paper

QuatCy: A Heptamethine Cyanine Modification With Improved Characteristics

Sopida Thavornpradit1, Syed Muhammad Usama1, G. Kate Park2, Jaya P. Shrestha1, Shinsuke Nomura2, Yoonji Baek2, Hak Soo Choi2✉, Kevin Burgess1✉

1. Department of Chemistry, Texas A & M University, Box 30012, College Station, TX 77842, USA
2. Gordon Center for Medical Imaging, Department of Radiology, Massachusetts General Hospital and Harvard Medical School, Boston, MA 02114, USA

This is an open access article distributed under the terms of the Creative Commons Attribution (CC BY-NC) license ( See for full terms and conditions.
Thavornpradit S, Usama SM, Park GK, Shrestha JP, Nomura S, Baek Y, Choi HS, Burgess K. QuatCy: A Heptamethine Cyanine Modification With Improved Characteristics. Theranostics 2019; 9(10):2856-2867. doi:10.7150/thno.33595. Available from

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Graphic abstract

A major restriction on optical imaging techniques is the range of available fluorophores that are compatible with aqueous media without aggregation, absorb light above 750 nm with high extinction coefficients, fluoresce with relatively high quantum yields, and resist photodecomposition. Indocyanine green (ICG or A in this paper) is an important example of a fluorophore that fits this description. Other dyes that are becoming increasingly prevalent are select heptamethine cyanine dyes (Cy7) which feature a cyclohexyl framework to rigidify the conjugated alkenes, and meso-chlorine substitution; MHI-148 (B) is one example.

Methods: Research described here was initiated to uncover the consequences of a simple isoelectronic substitution to MHI-148 that replaces a cyclohexyl methylene with a dialkyl ammonium fragment. Solubility experiments were carried out in aqueous and cell culture media, photophysical properties including fluorescence quantum yields, brightness and stability were measured. Moreover, in vivo pharmacokinetics, distribution and tumor seeking properties were also explored.

Results: Modification to incorporate dialkyl ammonium fragment leads to a brighter, more photostable fluorophore, with a decreased tendency to aggregation, complementary solubility characteristics, and a lower cytotoxicity.

Conclusion: All the above-mentioned parameters are favorable for many anticipated applications of the new dye we now call quaternary cyanine-7 or QuatCy.

Keywords: heptamethine cyanine, fluorescence imaging, tumor seeking, near-infrared