Tattoos may have more than an artistic or social expression message. A team of scientists in Germany have developed permanent dermal sensors that can be applied as artistic tattoos. As reported in the journal Angewandte Chemie, a colorimetric analytic formulation was injected into the skin instead of tattoo ink. The pigmented skin areas changed their color when blood pH or other health indicators changed.
The concept of using tattoos for diagnostic rather than cosmetic purposes was created by a research team led by Ali K. Yetisen, who works at the Technical University of Munich, Germany. He and his colleagues thought the technique could be useful in placing sensor formulations at spots in the body where they can record changes in metabolic substances directly, without any spatial distance or time delay, and for possibly extended time periods.
The researchers identified and adapted three colorimetric chemical sensors that produce a color change in response to biomarkers. The first sensor was a rather simple pH indicator comprising the dyes methyl red, bromothymol blue, and phenolphthalein. If injected into a model skin patch—a piece of pig skin—the resulting tattoo turned from yellow to blue if the pH was adjusted from five to nine.
The other two sensors probed the levels of glucose and albumin. Albumin is a carrier and transport protein in the blood. High body glucose levels may indicate diabetic dysfunction, whereas falling albumin levels can indicate liver or kidney failure. The glucose sensor comprised the enzymatic reactions of glucose oxidase and peroxidase, which, depending on the glucose concentration, led to a structural change of an organic pigment, and a change from yellow to dark green. The albumin sensor was based on a yellow dye that, upon association with the albumin protein, turned green.
To demonstrate the concept, the scientists applied several sensor tattoos onto patches of pig skin. When they changed the pH or the glucose or albumin concentrations, the colors of the decorated areas changed accordingly. They quantified these visible effects by evaluating the colors with a smartphone camera and an app.
The authors claim that such sensor tattoos could allow low cost, permanent monitoring of patients. With the development of suitable colorimetric sensors, the technique could also extend to recording electrolyte and pathogen concentrations or the level of patient dehydration. Further studies will explore whether tattoo artwork can be applied in a diagnostic setting.