"Our goal is to develop a non-invasive system that, when placed inside the blood cells of astronauts, will monitor continuously for radiation exposure or infectious agents," said James Baker, director of the centre. "Radiation changes the flow of calcium ions within white blood cells and eventually triggers irreversible cell death. It's important to monitor continuously for early signs of damage."

The University of Michigan scientists will build on work from a study currently under way for the National Cancer Institute. In that project the researchers are developing devices to sense premalignant and cancerous changes inside cells.

The devices consist of synthetic polymers called dendrimers and are less than 5 nm in diameter. Baker says that, because the nanosensors are so small, they pass easily into white blood cells (called lymphocytes), where they are in a perfect position to detect the first signs of biochemical changes caused by radiation.

"We can attach fluorescent tags to dendrimers, which glow in the presence of proteins associated with cell death," added Baker. "Our plan is to develop a retinal-scanning device with a laser capable of detecting fluorescence from lymphocytes as they pass one by one through narrow capillaries in the back of the eye." Baker reckons that a 15 s scan should be sufficient to detect radiation-induced cell damage.

Using nanosensors will remove the need for taking blood samples or implanting larger sensors that can cause inflammation. The devices are likely to be administered through the skin every few weeks, thus avoiding the use of injections.

If the first phase of the research succeeds, Baker plans to develop nanosensors that will monitor protein markers of infection in other immune system cells.