Composite Spin Probes with Adjustable Oxygen Sensitivity for Pulse EPR Imaging

Motivation: Solid crystalline probes, such as LiPc, allow repeated oxygen measurement using electron paramagnetic resonance (EPR). However, due to their short relaxation times at higher oxygen concentrations (>5%), they are not suitable for pulse EPR. Goal(s): The goal of this study was to develop a novel class of solid composite probes that enabled pulse EPR oxygen imaging (EPROI). Approach: We performed R1 and R2 measurements as a function of partial oxygen pressure (pO2). A selected probe was tested using in vivo Oxygen-enhanced EPROI and as a fiducial marker to outline tumor boundaries. Results: Composite probes demonstrate full physiological range oxygen imaging, opening new directions. Impact: We developed novel robust solid composite probes with adjustable oxygen sensitivity that allow pO2 imaging using pulse EPRI in full physiological range. Solid probe imaging will provide new insights where repeated and frequent oxygen measurements are needed.