Abstract: A sensor for measuring oxygen concentration in a tissue or an organ of a subject is provided. The sensor includes a sensory element comprising at least one paramagnetic spin probe compound encapsulated in a biocompatible oxygen permeable material. A barrier layer partially covers the sensory element and is comprised of at least one biocompatible oxygen impermeable material. Oxygen concentration data may be acquired by applying the sensor to the tissue or the organ of the subject, and subsequently applying a magnetic resonance spectroscopy or imaging technique.