Electron paramagnetic resonance and dynamic nuclear polarization of char suspensions: surface science and oximetry

Carbon chars have been synthesized in our laboratory from a variety of starting materials, by means of a highly controlled pyrolysis technique. These chars exhibit electron paramagnetic resonance (EPR) line shapes which change with the local oxygen concentration in a reproducible and stable fashion; they can be calibrated and used for oximetry. Biological stability and low toxicity make chars good sensors for in vivo measurements. Scalar and dipolar interactions of water protons at the surfaces of chars may be utilized to produce dynamic nuclear polarization (DNP) of the H-1 nuclear spin population in conjunction with electron Zeeman pumping. Low-frequency EPR, DNP and DNP-enhanced MRI all show promise as oximetry methods when used with carbon chars.