A recent Phys.org article noted a novel type of implantable sensor developed at Johannes Gutenberg University Mainz that employs gold nanoparticles to solve the issues of current sensors. The problem with implantable sensors that continuously transmit information on vitals is that they can’t remain in the body for more than a few weeks. Either the immune system rejects the device, or the sensors that use color to indicate concentration changes fade over time.
The new sensor uses color-stable gold nanoparticles that are modified with receptors for specific molecules. The nanogold is embedded in an artificial polymeric tissue and implanted under the skin. It then reports drug concentration changes by shifting color. Because they’re embedded in a porous hydrogel with a tissue-like consistency, they act like invisible tattoos that aren't rejected by the body. The gold nanoparticles aren’t visible with the naked eye, but can be viewed non-invasively through the skin with a special device.