A 'tooth tattoo' made from silk strands and gold wires could be used to detect life-threatening illnesses, researchers have said.
The tiny wireless device sticks to dental enamel and transmits real-time updates on chemicals in the breath and saliva.
Engineers at Princeton University in America have used it to detect bacteria that causes surgical infections and stomach ulcers, and say it could also be used to recognise viruses.
The sensor is in the early stages of development, but the university's researchers say it could one day be used to monitor human health with unprecedented accuracy.
During a demonstration, a volunteer breathed across a prototype sensor attached to a cow's tooth.
It generated an instant response which was sent to a nearby monitor.
"The antenna coil is what transmits the signal," said Michael McAlpine, the team's principal investigator, "you don't need a battery."
Details of the invention were reported in the medical journal Nature Communications.
The researchers created the device by bundling the silk and gold with graphene - an extremely thin sheet of carbon.
Yet despite its complexity, it can be applied to a tooth's surface with water "like a child's transfer tattoo", the university said.
The sensor is currently too big to fit onto a human tooth, and needs further work to scale it down.
The team also plans to improve the sensor so that it can withstand eating and brushing over a long period of time.
"Ideally, you want something that would be there for a while. We have a way to go before we could master that," Mr McAlpine said.