gold nanoparticles (IMAGE) Johannes Gutenberg Universitaet Mainz Caption Gold nanoparticles embedded in a porous hydrogel can be implanted under the skin and used as medical sensors. The sensor is like an invisible tattoo revealing concentration changes of substances in the blood by color change. Credit ill./©: Nanobiotechnology Group, JGU Department of Chemistry Usage Restrictions This image may only be used in connection with the press release "Tattoo made of gold nanoparticles revolutionizes medical diagnostics", issued by Johannes Gutenberg University Mainz on April 6, 2021. License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.