During surgery, doctors must be incredibly careful not to nick or cut the ureters — the two thin tubes that carry urine from the kidneys to the bladder. These tubes are hard to see, easy to damage, and when injured, can lead to serious complications for patients. Now, a team of researchers in Shenzhen, China may have found a clever solution: a dye that makes ureters glow bright enough for surgeons to spot them easily, for hours at a time.

The research was led by Professor Hongjie Dai at the University of Hong Kong in Shenzhen. His team developed a new fluorescent dye called SID-788, which lights up ureters under near-infrared cameras that surgeons already use in operating rooms, including robotic surgery systems. In tests on pigs — whose bodies are similar to humans — the glow remained visible for four to five hours, which is long enough for most abdominal and pelvic operations.

What makes SID-788 special is its design. The team threaded the glowing dye molecule through a ring made of α-cyclodextrin, a sugar-based material that the human body handles naturally. Think of it like sliding a bead onto a bracelet. This "sugar ring" keeps the dye from sticking to blood proteins or other tissues and helps it pass cleanly through the kidneys, leaving the body completely within hours.

Existing dyes had problems. One common option, called IRDye800CW, often fades quickly and can end up in the wrong parts of the body. Another, ZW800, clears through kidneys better but breaks down too easily. SID-788 avoids both issues. The sugar ring acts like armor, protecting the dye from chemical breakdown and light exposure.

Early safety tests look promising. Mice tolerated doses up to 500 times higher than the amount needed for actual surgery with no ill effects. The team has already scaled up production from lab-sized batches to gram quantities and is working with a contract research organization to move toward kilogram-scale production — a key step toward someday using the dye in real hospitals.

"Through its novel molecular design, SID-788 possesses properties long pursued by the NIR fluorescent dye field, solving some of the long-standing problems in this field," Dai said.

The research, published in Nature Photonics, was done in partnership with the University of Hong Kong-Shenzhen Hospital and Peking University First Hospital. Next up: more testing to bring this glowing tool from the lab into operating rooms around the world.