Scientists at a Cambridge, Massachusetts, laboratory who set out to develop a tattoo for tracking heart health may now be on track for developing a tattoo for people with diabetes that changes color as blood glucose levels rise and fall. If it becomes a workable approach, the tattoo technology could spare millions of people the tiresome, often painful routine of pricking themselves throughout the day to produce blood samples for their glucose monitors.
Draper Laboratories, a nanotechnology company, is working on an injectable ink that contains tiny particles (about 120 billionths of a meter across) whose three components interact to indicate BG levels. The first component is a glucose-detecting molecule; the second is a glucose-mimicking molecule; and the third is a dye that changes color depending upon the circumstances.
When injected into a person with diabetes, the particles move around “looking” for glucose. If the glucose-detecting molecules find mostly glucose-more likely if blood glocose levels are high-they turn the ink yellow. If glucose levels are low, the molecules latch on to the glucose mimics, producing a purple color. Ideally, say the researchers, healthy blood glucose levels will produce an “orangey” color.
The detection process, which is continuous as the nano-particles move about, takes only a few milliseconds. Even if it does not approach the accuracy of blood sample-based monitors, the tattoo could serve as both a warning system and a recovery monitoring system for too high or too low BG levels.
Draper scientists say that the tattoo would not have to be large or as deep as a conventional tattoo. Experiments on mice were scheduled in March 2010. The company says that it expects human trials to begin in 2011.
“It doesn’t have to be a large, over-the-shoulder kind of tattoo,” said scientist Heather Clark. “It would only have to be a few millimeters in size and wouldn’t have to go as deep as a normal tattoo.”
Clark and her colleagues didn’t set out to create a glucose-detecting ink.
“At first I didn’t even think it was possible,” said Clark.
Originally the scientists developed a sodium-sensitive ink to monitor heart health, advancing basic knowledge of electrolytes in the body, or to ensure athletes are properly hydrated.
Monitoring a single ion is easier than a complex molecule made of 24 atoms however. After speaking with a colleague, Clark decided to give glucose detection a try.
She started with the basic three-part system to detect sodium and modified to detect glucose. The nano ink particles are tiny, squishy spheres about 120 nanometers across. Inside the sphere are three parts: the glucose detecting molecule, a color-changing dye, and another molecule that mimics glucose. When the particles are dissolved in water they look like food coloring, says Clark.
The three parts continuously move around the inside the hydrophobic orb. When they approach the surface, the glucose detecting molecule either grabs a molecule of glucose or the mimicking molecule.
If the molecules mostly latch onto glucose, the ink appears yellow. If glucose levels are low, the molecule latches onto the glucose mimic, turning the ink purple. A healthy level of glucose has a “funny orangey,” color, according to Clark. The sampling process repeats itself every few milliseconds.
Time measured in milliseconds is much faster than then most current blood testing systems, and certainly less painful. But is it as accurate?
Glucose levels in the skin, where the ink would be injected subcutaneously, might not necessarily reflect the more critical measurement of glucose levels in the blood. Some studies show that skin glucose levels can lag up to 20 minutes behind blood glucose levels, while other show a much faster change.
“It’s an interesting question,” said Clark. “It’s one that we might even be able to help answer.”
Even if there is a significant lag time between blood and skin glucose levels, a small tattoo, in the several square millimeter range, according to Clark, would let diabetics know if an abnormally high or low reading was either returning to a normal level or getting worse.
