Melanin Radicals in Paraffin-embedded Melanoma Investigated Using Surface-type Dielectric Resonator for X-band EPR.

We investigated melanin radicals in paraffin-embedded malignant melanoma (MM) using a surface-type dielectric resonator for X-band electron paramagnetic resonance (EPR) and analyzed the radical species. The surface-type resonator's performance was examined using 5 - 10 μL of 0.1 mM 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPOL) aqueous solution in a 1.0-mm (i.d.) glass capillary as well as 1,1-diphenyl-2-picrylhydrazyl (DPPH) powder. The surface-type detection has approximately two times poorer S/N ratio than commercial insertion-type detection. A sample of the paraffin-embedded MM specimen was used for the radical detection. We obtained an EPR spectrum of melanin radicals in the paraffin-embedded melanoma sample (size ∼3 × 4 × 3 mm). A single line (∼0.64 mT peak-to-peak line-width) with a small shoulder was observed and was identified as a pheomelanin-related radical. The pheomelanin radical can be directly related to the MM. Thus, the present results were a good indication for noninvasive measurement, as well as for detailed analyses of melanin radicals in human MM.