In Vivo and in vitro EPR oximetry with fusinite: A new coal-derived,particulate EPR probe

The peak-to-peak line width (LW) of the first derivative electron spin resonance (EPR) spectrum of the coal maceral fusinite is reversibly broadened by O₂. The extent of broadening per unit of partial pressure of oxygen (pO₂) is unusually large, exceeding that of nitroxides by almost two orders of magnitude. This paramagnetic properly of fusinite, combined with its very stable physicochemical properties and low toxicity, is shown to be of utility in the measurement of pO₂ in vitro and in vivo. Fusinite particles are endocytosed by Chinese hamster ovary (CHO) cells in vitro; this is useful for intracellular O₂ measurements with commercially available EPR spectrometers operating at 9.1-9.3 GHz. For measurement of oxygen in vivo using low frequency EPR (1.l-1.3 GHr), fusinite provides a sensitive and persistent means to measure pop in tissues. Particles implanted into the gastrocnemius muscle of NJ mice remained interstitially in the same position for months with undiminished sensitivity to pO₂ and no specific toxic effects.