Cornell University engineers believe the new technology could help surgeons remove tumours more effectively.
The spheres are made of silica, a glass-like material, and are coated with a dye that glows when exposed to light.
The spheres are then attached to antibodies that target specific proteins on cancer cells.
When the spheres bind to the cancer cells, they light up, making the tumours visible to surgeons.
The researchers say the spheres are small enough to pass through the tiny blood vessels that feed tumours, and are bright enough to be seen even through thick tissue.
They also say the spheres are safe for use in patients.
The researchers are now planning to test the spheres in clinical trials.
If the trials are successful, the spheres could be used to help surgeons remove a variety of tumours, including brain, breast, and prostate cancer.
"We are excited about the potential of this technology to help surgeons remove tumors more effectively," said Professor Ulrich Wiesner, who led the research team.
"We believe that these spheres could make a real difference in the lives of cancer patients."
