Fluorescence Lasts Four Times Longer During Surgery... KRICT Develops Next-Generation Near-Infrared Fluorescent Dye [Reading Science]

Overcoming 'Photobleaching' Limitations of FDA-Approved ICG: Improving Accuracy in Long Cancer Surgeries
Fluorescence Retention Time Improved Fourfold, Over 90% Cell Viability
Featured as Cover Paper in the International Journal 'Small'

A domestic research team has solved the issue of rapid fading that occurs when near-infrared fluorescent dyes used to detect the location of cancer or lymph nodes during surgery are exposed to light. By enhancing fluorescence retention performance by more than four times compared to conventional fluorescent dyes, it is expected that target areas can be stably identified even during lengthy surgical procedures.

On July 19, the Korea Research Institute of Chemical Technology announced that the research team led by Dr. Park Young-il and Dr. Nam Sang-hwan, in collaboration with Professor Sung Jin Park's group at the Georgia Institute of Technology in the United States, has developed a next-generation phosphor by redesigning the molecular structure of the near-infrared fluorescent dye 'indocyanine green (ICG)' into a polymer to significantly improve photostability.

Near-infrared imaging technology explanation. Provided by the research team.

The results of this research were published as the cover paper in the June 2026 issue of the international journal "Small" in the field of nano and micro materials.

Currently, indocyanine green is the only near-infrared fluorescent dye approved by the U.S. Food and Drug Administration (FDA). Since its approval in 1959, it has been used in various surgeries and diagnoses, including lymph node mapping for breast cancer, liver cancer resection, and biliary tract visualization.

Near-infrared light (wavelengths approximately 650–900 nm) penetrates human tissue more deeply than visible light, so when used with fluorescent dyes, it can visualize biological tissue several centimeters below the surface.

However, conventional ICG has the limitation of undergoing 'photobleaching,' where its fluorescence rapidly weakens when exposed to a surgical laser for extended periods. As a result, the dye must be repeatedly administered during long surgeries.

Redesigned with Polymer Structure... Four Times Higher Fluorescence Retention

The research team addressed this problem by tethering ICG molecules to a polymer chain, thereby fixing the fluorescent structure in a stable manner.

The newly developed phosphor, 'KR-NIR-P,' blocks oxygen access with its polymer skeleton and keeps the molecular structure stable, allowing its fluorescence to be maintained much longer under the same illumination. It also prevents molecular aggregation, reducing factors that accelerate photobleaching.

Experimental results showed that when exposed continuously to a 785 nm near-infrared laser, conventional ICG exhibited a drop in fluorescence to about 40% of its initial intensity within 50 seconds, whereas KR-NIR-P maintained 66% of its fluorescence even after 200 seconds. This means its photostability improved more than fourfold compared to the conventional dye.

It also showed low cytotoxicity. In both cancer cells, such as cervical cancer and oral squamous cell carcinoma, and normal cells, cell viability remained above 90% at concentrations up to 20 micromolar (μM), demonstrating high biocompatibility.

Demonstrated Potential for Long-Term Tracking of Cancerous Lymph Nodes

In a three-dimensional tumor spheroid experiment that mimics real tumors, the research team observed that KR-NIR-P penetrated uniformly into deep tissue layers.

In mouse experiments, fluorescence was detected in lymph nodes two hours after subcutaneous injection into the footpad and became even more strongly concentrated after 24 hours. This indicates the potential for real-time, long-term tracking of lymph nodes, which are the pathways for cancer metastasis.

Photo of the research team. (From right) Nam Sanghwan, Principal Researcher at Korea Research Institute of Chemical Technology; Park Youngil, Principal Researcher; Choi Minseok, Researcher. Courtesy of Korea Research Institute of Chemical Technology

The research team plans to further verify safety and efficacy through additional preclinical studies such as toxicity evaluation and pharmacokinetic analysis.

Park Young-il, Principal Researcher at Korea Research Institute of Chemical Technology, stated, "The key of this study is slowing down the destruction rate of the fluorescent structure exposed to light by polymerizing the ICG molecule. It is expected to enable more stable medical imaging, even during long surgeries."

Shin Seok-min, President of Korea Research Institute of Chemical Technology, added, "The polymerization strategy we developed can be applied not only to ICG but also to a variety of fluorescent dyes. In addition to medical imaging, it could expand its application to next-generation fluorescent materials for anti-counterfeiting and security purposes as well."

This content was produced with the assistance of AI translation services.