Oxygen sensing using time-domain X-ray luminescence.

Oxygen tension is a critical physiological parameter in deep tissues; however, high-resolution and non-invasive measurement of oxygenation remains challenging. In this study, we developed a prototype for a lifetime measurement system based on a pulsed carbon nanotube X-ray source to evaluate X-ray-excited luminescence oxygen sensing. The X-ray irradiated a PDMS fiber containing the rapidly responding X-ray scintillator cerium-doped lutetium orthosilicate (LSO) and an oxygen sensing dye, (Pt(II) meso-Tetra(pentafluorophenyl)porphine (PtTFPP)), that is excited by the LSO X-ray luminescence and emits red fluorescence quenched by oxygen. At 0 kPa oxygen tension, the sensor showed a lifetime of approximately 62 μs, while at 21 kPa oxygen, the emission was strongly quenched with an estimated lifetime less than 1.33 μs. Covering the oxygen-sensing fiber with chicken breast tissue slices from 1.4 to 8.3 mm thick had minimal effect on measured luminescence lifetime in deoxygenated conditions (lifetime of 62.0 ± 6.1 μs). Control measurements using gadolinium oxysulfide doped with europium (GOS:Eu) powder also confirmed thickness-independent lifetime behavior. These results demonstrate that X-ray-excited lifetime measurement depends primarily on oxygen concentration and is independent of tissue thickness, supporting the feasibility of deep-tissue oxygen sensing and future time-domain X-ray luminescence computed tomography (XLCT) imaging for three-dimensional oxygenation mapping.