An oxygen-sensing probe for the emerging medical technology in vivo EPR has been made by scientists in the US and India.

The probe, made by Periannan Kuppusamy and his colleagues at the Ohio State University and the Indian Institute of Technology, Chennai, is biologically stable, non-toxic and sensitive to the amount of oxygen in its surroundings.

The probe is made of lithium and macrocyclic organic groups, and has an unusual crystal structure with channels running lengthwise through it. The probe is injected into the tissue, and oxygen molecules can enter the channels, disturbing the magnetic properties of the material. Kuppusamy used electron paramagnetic resonance (EPR) spectroscopy to measure these changes, which gives a very accurate measurement of the amount of oxygen in the probe's environment.

Although the use of in vivo EPR is currently limited to small animals, Kuppusamy is upbeat about the potential uses for his new probe. 'There is a great need for reliable and non-invasive measurements of oxygen levels in body tissues,' he said, 'because oxygen imbalances result in conditions within the tissues that are implicated in illnesses such as heart attacks and strokes.'

'We have just completed some studies establishing the use of this probe for non-invasive tracking of stem cells labelled with it, and in situ measurements of oxygen concentration of transplanted stem cells in infarcted hearts [hearts with dead tissue resulting from a loss of blood supply],' he added.

Bernard Gallez, director of the Biomedical Magnetic Resonance Unit at the University of Louvain, Belgium, welcomed their findings. 'This work is excellent, offering a convincing interpretation about the mechanisms by which some paramagnetic materials may act as oxygen sensors,' he said. 'Kuppusamy has established a rational basis for measuring these essential molecules in biological systems using in vivo EPR.'

Kuppusamy is now investigating other materials with similar properties, and using the probe to investigate cardiovascular disease.

Susan Batten