Korean researchers develop next-generation fluorescent dye for cancer surgery with 4x longer imaging stability

South Korean researchers have developed a technology that overcomes a key drawback of fluorescent dyes used in cancer surgery and angiography — the tendency for imaging clarity to fade rapidly during procedures.

A research team led by Park Young-il and Nam Sang-hwan of the Korea Research Institute of Chemical Technology announced Sunday that, working with a team led by Professor Park Sung-jin at Georgia Tech, they had redesigned the near-infrared fluorescent dye indocyanine green (ICG) using a polymer structure to produce a fluorophore with significantly improved photostability.

Near-infrared light, with wavelengths of roughly 650 to 900 nanometers, penetrates human tissue more deeply than visible light because water and hemoglobin in the body absorb less of it. Combining this property with fluorescent dyes allows imaging of biological tissue several centimeters beneath the surface.

ICG is currently the only near-infrared fluorescent dye to have received FDA approval anywhere in the world. However, ICG suffers from "photobleaching" — its fluorescence fades quickly under light exposure — which can reduce accuracy during lengthy surgeries. Previous attempts to address this by encapsulating ICG in microparticles or nanostructures were hampered by complex manufacturing processes and dye leakage, limiting their commercial viability.

The research team solved the problem by attaching ICG molecules to polymer chains, anchoring the fluorescence-generating sites on both sides to extend their stability.

ICG loses its fluorescence when intense laser light causes the heptamethine ring responsible for emission to break down through reaction with surrounding oxygen. In the team's new fluorophore, KR-NIR-P, the polymer backbone blocks oxygen from reaching the chromophore. Hydrophobic interactions between molecules hold the structure stable, allowing fluorescence to persist longer under the same light conditions. The polymer structure also prevents uncontrolled molecular aggregation, eliminating another factor that accelerates photobleaching.

In experiments using a 785-nanometer near-infrared laser, conventional ICG saw its fluorescence drop sharply to 40 percent of its original intensity within 50 seconds, while KR-NIR-P retained 66 percent even after 200 seconds — a more than fourfold improvement in photostability.

Cytotoxicity tests also yielded strong results. KR-NIR-P maintained cell viability above 90 percent at concentrations up to 20 micromoles (µM) in both cancer cells — including cervical cancer and oral squamous cell carcinoma — and normal cells, confirming high biocompatibility. Changes in key proteins associated with cell death were comparable to those seen with conventional ICG, indicating the new dye does not induce cytotoxicity.

When introduced into three-dimensional tumor spheroids — artificial cell clusters that mimic actual tumors — KR-NIR-P penetrated uniformly to deep layers. In mouse studies, fluorescence was detected in lymph nodes two hours after subcutaneous injection into the footpad and accumulated strongly after 24 hours, demonstrating the dye's potential for real-time tracking of lymph nodes, which serve as pathways for cancer metastasis.

"The significance lies in our success in slowing the rate at which the chromophore is destroyed by light, by polymerizing the ICG molecule," Park Young-il said. "It will be possible to develop this into a fluorescent contrast agent for medical imaging after further preclinical and clinical trials."

The findings were published as the cover paper of the June 2026 issue of Small, a leading international journal in the field of nano and micro materials.