Development of an innovative 9 GHz EPR surface detection method and its application to non-invasive human fingers and...

We developed an innovative surface-type cavity for 9 GHz electron paramagnetic resonance (EPR) and used it to non-invasively measure human fingers and nails. This surface-type cavity measures a sample on the top of the cavity instead of a sample inserted into the cavity. To verify the performance of this method, 5-10 μL of 0.1 mM 4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPOL) aqueous solution in a 1.0-mm (i.d.) glass capillary was used. Although the detectable radical concentration of the surface-type cavity is lower than that of a commercial cavity, the surface-type cavity can measure biomedical samples. In addition, the cavity is capable of measuring human fingers and nails. The dynamics of a topically applied 1.0-mM TEMPOL solution with a commercial lotion (5:1 by weight) on a human finger and nail were investigated. The present EPR results suggest that TEMPOL in solution may not easily permeate into the finger and nail during the measurements. Therefore, 9 GHz surface-type detection exhibits the good potential to study paramagnetic species in bulky biomedical samples.