A Miniature Electron Spin Resonance Probehead for Transcutaneous Oxygen Monitoring

Oxygen concentration in the skin is an important clinical indicator for monitoring pathological conditions such as chronic wounds, skin cancer, and peripheral vascular disease. Currently, the only clinically approved method for acquiring these oxygen levels is based on electrochemical measurements that employ Clarke-type electrodes attached to the skin. This technique has many drawbacks and limitations, making it unattractive for standard medical practice and care. Electron spin resonance (ESR), which can obtain the oxygen concentration through measurements of the spin–spin relaxation time (T ₂) of paramagnetic species interacting with molecular oxygen, provides a possible alternative. However, a traditional ESR setup requires a large homogenous static magnetic field source with limited gap between the poles and complicated equipment, making it unattractive for clinical use. Here, we present a new design for a miniature ESR probehead, which is comprised of a specially designed permanent magnet and a small microwave resonator. The small size of the probehead (36 mm diameter cylinder with a height of 24 mm) enables transcutaneous measurements from virtually any part of the skin. Compared to the electrochemical method, this ESR-based approach may provide faster and more accurate readings of oxygen concentration in the skin, making it highly attractive for future clinical use.