For many years, scientists in many countries have been developing devices that can read a person’s state of health, such as temperature, blood pressure and brain activity. Such devices make life much easier for people who have to be under the constant supervision of doctors and who have chronic diseases. As a rule, such sensors are attached to the skin or applied as tattoos, which can change color when the chemical composition of the blood changes. The problem with these sensors is that they are not long-lasting. They can wash off with water, be rejected by the body and require constant renewal.

Researchers at Mainz University in Germany have developed a tattoo on gold nanoparticles. This invisible gold tattoo, the size of a coin and less than a millimeter thick, picks up the slightest changes in blood composition when exposed to drugs or when the patient’s condition changes. Gold nanoparticles are immersed in a special polymer, which is placed under the skin in the form of an implant. Immersed in a porous gel, they remain under the skin in one place and are not destroyed by immune cells.