Encapsulation of a highly sensitive EPR active oxygen probe into sonochemically prepared microspheres

A solution of perchlorotriphenylmethyl triester (PTM-TE, a stable organic free radical) dissolved in hexamethyldisiloxane (HMDS) is encapsulated by using high-power ultrasound into a polymerized shell of bovine serum albumin (BSA). It is found that the method leads to an overall loss of EPR signal intensity from the washed suspension of microspheres and the encapsulated PTM-TE/HMDS solution is found to be sensitive to the partial pressure of oxygen in the muscle and tumor tissue of mice.