Measurement of pH under skin

Kroll et al. used X-band spectral/spatial EPRI together with pH-sensitive nitroxide probes to study the microacidity of rat and human skin biopsies. A dose of nitroxide solution was placed on the skin surface and allowed to penetrate into the sample prior to the commencement of EPRI measurements. Magnetic field gradients were applied perpendicular to the skin surface, in order to allow spatial discrimination within the various layers of the skin. Local pH was deduced from the spectral axis of the spectral/spatial data, by determination of the hyperfine coupling constant, which is pH-sensitive in these compounds. Plots of pH versus depth into the skin could be produced, and the shape of the curves was found to change under the influence of topical drug treatment. This preliminary study showed the potential for one-dimensional pH imaging in the skin, a tool that is likely to be of use to the pharmaceutical industry. 

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