Indocyanine Green (ICG, IC Green, Foxgreen) is a negatively charged tricarbocyanine dye widely used for imaging and flow cytometry due to its low toxicity and near-infrared fluorescence emission.

ICG has an absorption maximum at 787 nm with slight absorption in the visible range and a fluorescence emission maximum at 819 nm. The minimal light scattering and low autofluorescence in this spectral range result in a significantly reduced background and improved signal-to-noise ratios, thereby enhancing detection sensitivity.

ICG and its derivatives are utilized for imaging purposes, as their infrared fluorescence emission can penetrate tissues up to several millimeters, enabling effective deep tissue and small animal in vivo imaging. In medical diagnostics, ICG is employed to assess cardiac output, hepatic function, liver and gastric blood flow, and ophthalmic angiography. ICG is also used for linking with antibodies to target cancer cells and tumors.