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

Area of Science:

• Biomaterials Science
• Nanotechnology
• Biophysics

Background:

• Developing sensitive and stable probes for oxygen partial pressure (pO2) is crucial for understanding physiological and pathological processes.
• Stable organic free radicals, like perchlorotriphenylmethyl triester (PTM-TE), offer unique properties for sensing applications due to their paramagnetic nature.
• Encapsulation techniques are essential for protecting sensitive molecules and enabling their targeted delivery in biological systems.

Purpose of the Study:

• To develop a novel method for encapsulating a stable organic free radical (PTM-TE) within biocompatible microspheres.
• To assess the oxygen sensitivity of the encapsulated PTM-TE within the microspheres.
• To evaluate the utility of these microspheres for in vivo oxygen partial pressure measurements in biological tissues.

Main Methods:

• High-power ultrasound (20 kHz) was employed to encapsulate a solution of perchlorotriphenylmethyl triester (PTM-TE) in hexamethyldisiloxane (HMDS) into polymerized bovine serum albumin (BSA) microspheres.
• Microsphere size distribution was characterized, ranging from 0.5 to 3 microm, with a peak at approximately 1.2 microm.
• Electron paramagnetic resonance (EPR) spectroscopy was used to analyze the PTM-TE signal and its sensitivity to oxygen partial pressure before and after encapsulation.

Main Results:

• The encapsulation process yielded microspheres with a controllable size distribution.
• While encapsulation led to a decrease in overall EPR signal intensity, the encapsulated PTM-TE/HMDS solution retained its sensitivity to external oxygen partial pressure.
• The developed BSA microspheres demonstrated efficacy in determining oxygen partial pressure within the muscle and tumor tissues of mice.

Conclusions:

• Ultrasound-mediated encapsulation is an effective method for creating oxygen-sensitive PTM-TE/HMDS-loaded BSA microspheres.
• These microspheres maintain their oxygen sensing capabilities after encapsulation, despite a reduction in signal intensity.
• The developed microspheres represent a promising tool for non-invasive in vivo assessment of oxygen partial pressure in various biological tissues, particularly in the context of disease states like tumors.