Electron spin resonance investigation of laser and heated metal‐tip–induced free radical formation in various tissues

The short‐lived free radical formation accompanying laser irradiation and laser‐heated metal tip contact was examined using electron spin resonance (ESR) spin‐trap methodology. Various tissues (canine myocardium, human aorta, liver, and spleen) were irradiated by argon‐ion (continuous wave [CW] and pulse) and YAG (CW) lasers employing both naked fiber and a laser‐heated metal tip. All showed the formation of primarily carbon‐centered, not oxygenated, free radicals, together with some minor unidentified species. This implies that the backbones of amino acids, lipids, or other biological building blocks are cleaved during the irradiation or thermal treatment. Different tissues produce similar radicals but with different amounts when irradiated by argon‐ion, YAG, and laser‐heated metal tip sources. The amount of the free radicals formed depends on the laser power (within 5–15 W). Compared to the naked fiber, the laser‐heated metal tip shows the generation of at least twice the amount of free radicals. The possible relationship of the free radical formation to tissue injury is briefly discussed.