Stanford Univ. scientists developed new molecular fluorescent dyes capable of being injected into the patient that both improve imaging depth and safety compared to previous dyes.

“Fluorescent imaging of biological systems in the second near-infrared window (NIR-II) can probe tissues at centimeter depths and achieve micrometer-scale resolution at depths of millimeters,” the researchers wrote in their paper appearing in Nature Materials. “Unfortunately, all current NIR-II fluorophores are excreted slowly and are largely retained within the reticuloendothelial system, making clinical translation nearly impossible.”

The technology has potential use as a diagnostic tool.

Already, dyes are used in the medical field. Doctors inject a dye into patient’s bloodstream in an eye test known as fluorescein angiography. The dye travels from the arm to the blood vessels in the eyes in a matter of seconds, giving doctors a view into the blood vessels’ configuration.

For a while, researchers have worked at creating dyes that emit long wavelengths near infrared light. Such a dye would be capable of being viewed via a special camera and projected on a monitor. The long wavelengths ensure the light escapes from the skin with negligible scattering, allowing for better images.   

However, there are safety concerns. According to Stanford Univ., “Some (dyes) made from carbon nanotubes or quantum dots can linger in the body for days and months, caught in the liver and spleen, before being excreted slowly.” This has prevented the technologies implementation in humans.

The new dye, according to the researchers, is 90% excreted through the kidneys within 24 hours. “The fluorophore outperformed indocyanine green (ICG)—a clinically approved NIR-I dye—in resolving mouse lymphatic vasculature and sentinel lymphatic mapping near a tumor,” the researchers wrote.

“The difficulty is how to make a dye that is both fluorescent in the infrared and water soluble,” said Alex Antaris, the first author of the paper. “A lot of dyes can glow but are not dissolvable in water, so we can’t have them flowing in human blood. Making a dye that is both is really the difficulty. We struggled for about three years or so and finally we succeeded.”    

The researchers believe the dye has applications as a surgical guide, as it can be captured in video in real-time.