A glowing tat, but not a rad tat. (via flickr)
Imagine the challenge of developing a chemical monitor to implant beneath the skin. The technology would provide non-invasive, constant monitoring of glucose in diabetic patients instead of current sporadic measurements requiring blood withdrawal. But its development is a rubix cube—all aspects of the puzzle must be considered with every turn; focus on one face and the other five will be a mess.
Smart tattoos, as they are called, won’t be developed overnight. But researchers explain how clinical applications are a step closer in a paper published this summer in the journal Analytical Chemistry.
Different mechanisms can be applied for in vivo glucose monitoring. Dr. Heather Clark, an associate professor at Northeastern University, is studying nanoparticles which contain highly fluorescent molecules. As glucose flows into the particles it displaces the fluorophore and reduces the amount of light being emitted. Dr. Clark says fluorescence “is the most sensitive optical technique for these types of measurements.”
Dr. Mike McShane, an associate professor of biomedical engineering at Texas A&M University, employs a different strategy for glucose monitoring. The particles created in his lab are enzyme based. The phosphorescence of a molecule embedded in the particle turns off in the presence of oxygen. Glucose entering the particle reacts with an enzyme which requires oxygen. Oxygen depletion, and therefore glucose concentration, can be measure by intensity of the light emitted when phosphorescence is turned on.
The feasibility of smart tattoo technology was demonstrated two years ago when Dr. Clark and colleagues published a paper showing images of tattooed rats drinking sugar solutions. As time elapsed the intensity of the tattoo’s glow fluctuated. Glucose concentrations measured by the emission from the tattoos correlated with concentrations measured by the conventional blood withdrawal method.
Researchers have since grappled with the technology’s limitations. Dr. Clark addressed one issue in a June publication discussing particle materials which “have favorable characteristics for in vivo applications,” bringing the tattoos closer to fruition. But Dr. McShane acknowledges, “It is a major materials challenge to find a way to get these particles into human tissue.”
Another complication is the particles’ size. Nanoparticles allow glucose diffusion that is representative of blood concentrations, but the particles are so small they migrate from the injection site within hours. “Larger materials are more consistent with current clinical applications,” explains Dr. McShane. “Like dermal fills used in cosmetics.”
So your doctor’s office won’t include a tattoo parlor anytime soon. Dr. McShane admits that although there are industries interested in his and Dr. Clark’s work, the challenge will be developing biosensors that maintain a stable response overtime. Dr. Clark says, “We don't have a good estimate yet on when we would be ready for clinical trials, but it would be years, not months, away.” That allows plenty of time for design considerations on your rad—short for radiative, of course—tat.
Rebecca Guenard is formerly a chemistry professor and currently a science writer. She maintains the humorous science blog Atomic-o-licious, aimed at simultaneously entertaining and educating nonscientists.
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