Indocyanine Green

Product Overview

Indocyanine Green (abbreviated ICG) is a water-soluble tricarbocyanine polymethine dye, marketed under names such as Cardiogreen, IC Green and Foxgreen. It is currently the only near-infrared fluorescent dye approved for clinical use.

Structural characteristics: The molecule consists of two benzo[e]indolium chromophores connected by a conjugated heptamethine chain, with a 4-sulfobutyl hydrophilic side chain at each end, existing overall as an inner salt (zwitterion) containing one sodium ion. This structure determines its two core properties:

1. Near-infrared optical window — the conjugated heptamethine chain pushes its absorption and emission into the near-infrared region (excitation approximately 780–805 nm, emission approximately 830 nm). At these wavelengths, tissue penetration depth is significantly greater than visible light, and both tissue autofluorescence and hemoglobin absorption are low, yielding a high signal-to-noise ratio.
2. Amphiphilicity and protein binding — the molecule is negatively charged and “pseudofluorogenic”: free dye fluoresces weakly, but fluorescence is markedly enhanced upon non-covalent binding to plasma proteins (mainly albumin); at the same time, protein binding confines it to the intravascular space, making it an ideal tracer for blood vessels and blood flow.

In vivo disposition: After intravenous injection it rapidly binds plasma proteins and remains intravascular; it is selectively taken up by hepatocytes, excreted unchanged in bile, does not undergo enterohepatic circulation, and is not excreted by the kidneys. Its plasma clearance rate therefore directly reflects liver function and hepatic blood flow.

Why its clinical position is unique: Among near-infrared fluorescent dyes, ICG is one of the very few with comprehensive human safety data and regulatory approval, making it the standard reagent in liver function assessment, hemodynamic measurement, ophthalmic angiography and the recently emerged field of fluorescence-guided surgery.

Technical Specifications

• Standards: CHP/USP/EP; Chinese national drug standard WS-033(X-27)-92 (Indocyanine Green)

• Specification: 0.99 (purity ≥99.0%, HPLC); for pharmacopoeial/injectable use, calculated on the dried basis, the content of C₄₃H₄₇N₂NaO₆S₂ should be 94.0%–105.0% (this wide range is a statutory characteristic of dye substances and differs in meaning from “chemical purity”; care must be taken in procurement and testing)

• CAS No.: 3599-32-4 (EINECS/EC 222-751-5; MDL MFCD00013078; Beilstein 4115884; Merck Index 14,4962; PubChem CID 5284572; ChEBI 31696; KEGG DRUG D01342; MeSH D007208)

• Molecular formula: C₄₃H₄₇N₂NaO₆S₂

• Molecular weight: 774.96 (Sigma-Aldrich 774.96; TCI 774.97; ECUST database 774.963; MP Biomedicals 774.98); the 774.96/774.97/774.98 differences at the second decimal place among sources are due to rounding and calculation precision

• Appearance: Dark green-cyan or dark brownish-red powder (also described as green to greenish-brown powder); odorless; TCI lists it as a solid (20 °C). Readily degraded by light and heat

• Purity (HPLC): ≥ 99.0%; for injectable use, 94.0%–105.0% calculated on the dried basis

• Melting point: 235 °C (Baidu Baike / Chinese Pharmacopoeia-related entries; recommended value). Other sources do not record a melting point and rely primarily on spectral identification — as a dye, this product shows a marked tendency to decompose on heating, melting point is often not a primary release criterion, and actual quality control relies mainly on absorption spectrum, loss on drying and assay

• Specific optical rotation: Not specified — the molecule has C=C geometric isomerism (the heptamethine chain is all-trans), but no chiral center; pharmacopoeias substitute spectral and chromatographic identification

• Chemical name: 1H-Benzo[e]indole, 2-[7-[1,3-dihydro-1,1-dimethyl-3-(4-sulfobutyl)-2H-benzo[e]indol-2-ylidene]-1,3,5-heptatrienyl]-1,1-dimethyl-3-(4-sulfobutyl)-, hydroxide, inner salt, sodium salt

• Identification (Chinese standard WS-033(X-27)-92):

  • Dissolve approximately 10 mg in 5 mL of water, add 10 drops of sodium hydroxide test solution, heat to approximately 60 °C, add 10 drops of hydrogen peroxide solution — a dark reddish-brown color appears immediately, gradually turning orange-yellow on standing
  • After ignition, it shows the identification reactions of sodium salts and sulfates
  • The solution under the Assay item, determined by spectrophotometry, exhibits maximum absorption at 216, 263 and 784 nm

• Tests: Loss on drying — dry a sample under reduced pressure at 50 °C for 3 hours; weight loss not more than 6.0%

• Solubility: Soluble in water or methanol; practically insoluble in acetone; other sources report slightly soluble in water. Reagent grade is soluble in DMSO (approximately 1 mg/mL or higher, batch-dependent)

• Spectral characteristics: λmax 216, 263, 784 nm (recorded in the Chinese standard); other sources report 265 nm (similar in value to the λmax of steroids such as calcitriol, but a different substance — do not confuse). Excitation/emission approximately 780–805 nm / approximately 830 nm (near-infrared region)

• Computed physicochemical parameters: LogP approximately 10.56; hydrogen bond acceptors 7 / donors 0; topological polar surface area approximately 137.41 Ų

• Formulation presentation (marketed product): Indocyanine green for injection (lyophilized powder), commonly 25 mg/vial, dissolved in water for injection immediately before use

• Storage conditions: Store protected from light, sealed; TCI recommends room temperature (cool, dry place below 15 °C), storage under inert gas protection, and explicitly states moisture must be avoided (decomposition); MP Biomedicals recommends room temperature (15–30 °C), stored dry

Applications

• Liver function testing (core classic use): After intravenous injection, measurement of the blood disappearance rate (K_ICG) and 15-minute retention rate (R15_ICG) is used to assess hepatic reserve function, hepatic blood flow and hepatocyte uptake/excretion capacity — a commonly used indicator for preoperative evaluation before hepatectomy and for judging severe hepatic dysfunction

• Cardiac output measurement and hemodynamics: Measurement of cardiac output, circulating blood volume and hepatic blood flow by the dye dilution method; also used for cardiovascular angiography

• Ophthalmic angiography (ICGA): For choroidal angiography, evaluating fundus diseases such as choroidal neovascularization and polypoidal choroidal vasculopathy — because near-infrared light penetrates the retinal pigment epithelium and hemorrhagic layers, it offers advantages over sodium fluorescein angiography

• Fluorescence-guided surgery and lymphatic imaging: For sentinel lymph node localization (breast cancer, gastric cancer, colorectal cancer, etc.), tumor margin delineation, bile duct and liver segment staining in hepatobiliary surgery, and flap perfusion assessment in plastic and reconstructive surgery

• Intraoperative fluorescence angiography: For assessing tissue perfusion and anastomotic blood supply (e.g., gastrointestinal anastomoses, graft patency assessment in coronary artery bypass grafting)

• Analytical chemistry and protein research: As a “pseudofluorogenic” dye — fluorescence is markedly enhanced upon non-covalent protein binding — it can be used for protein quantification by capillary electrophoresis with laser-induced fluorescence detection, and has been applied to the separation and analysis of various labeled proteins including human serum albumin, ribonuclease A, transferrin and cytochrome c

• Other research uses: As an intraocular lens capsule staining agent; as a photosensitizer in photothermal/photodynamic therapy research; targeted delivery and imaging studies after encapsulation in nanocarriers (e.g., liposomes, micelles)

• Formulation and manufacturing: For formulation development of lyophilized powder for injection; the core control points for dye APIs are photothermal degradation and moisture-induced decomposition — the entire production process requires strict light protection, inert gas protection, low-temperature drying environment and moisture control (loss on drying ≤6.0%); quality control centers on absorption spectrum (characteristic peaks at 216/263/784 nm), assay (94.0%–105.0% on the dried basis) and loss on drying; suitable for analytical method development and validation, stability studies, and GMP scale-up and CMO/CDMO contract manufacturing

Safety notice: This product is an active pharmaceutical ingredient (API) / diagnostic dye intended solely for legitimate industrial, research and pharmaceutical manufacturing use, and does not constitute end-user clinical or self-administration guidance. Important safety information: ICG formulations containing sodium iodide (NaI) are contraindicated in patients with iodine allergy (this CAS entry corresponds to the pure dye IC Green; actual injectable formulations may contain sodium iodide — verify the specific formulation composition before use); contraindicated in patients allergic to this product. Adverse reactions: Occasional allergic reactions (rash, urticaria, pruritus), nausea, vomiting, hypotension, shock, transient fever and chills; severe allergic reactions are rare but can be fatal — anti-allergy rescue measures must be available during use. Precautions: ① Solutions should be prepared immediately before use and should not be stored after reconstitution (the dye has limited stability in aqueous solution); ② readily degraded by light and heat — preparation and infusion should be protected from light; ③ although not renally excreted, caution is still required in patients with renal insufficiency who have a concomitant allergic diathesis; ④ use in pregnancy and lactation must be weighed by a physician. When handling the API, wear protective gloves, protective clothing and eye/face protection, and avoid dust inhalation; store protected from light, moisture and under inert gas protection. Some sources carry a California Proposition 65 carcinogen warning (www.P65Warnings.ca.gov); operators should comply with local regulatory requirements.

Product information: please contact us. This information is for reference only.