Evaluation of oxygen-response times of phthalocyanine-based crystalline paramagnetic spin probes for EPR oximetry

Abstract

The goal of the present study was to evaluate the temporal response of particulate-based EPR oximetry probes to changes in partial pressure of oxygen (pO 2 ). In order to accurately evaluate the oxygen-response time, we developed a method for rapid modulation of pO 2 in a chamber containing the probe using an oscillator-driven speaker-diaphragm setup. The apparatus was capable of producing sinusoidal changes in pO 2 at frequencies up to 300 Hz or more. The pressure-modulation setup was used to evaluate the temporal response of some of the most commonly used phthalocyanine-based particulate probes. For validation, the time-response of the probes was compared to that of a high sensitivity pressure sensor. The results revealed that some particulate probes could respond to changes in pO 2 with a temporal response of 3.3 ms (300 Hz). The observations were interpreted in the light of their crystalline packing in favor of oxygen diffusion. The results of the present study should enable the selection of probes for oximetry applications requiring high temporal resolution.

Fabrication and physical evaluation of a polymer-encapsulated paramagnetic probe for biomedical oximetry

“…The response time of the chip when the gas was switched from oxygen to nitrogen was long enough (120 s) that the time to manually switch gas (1–2 s) did not significantly affect it, but may affect the response time when switching from nitrogen to oxygen (5 s). The speed of responses to changes in pO 2 can be measured with greater accuracy using audio speaker-mediated pressure modulation, as previously described (Vikram et al 2008). This system produces very rapid and controllable fluctuations in pO 2 (on the order of 200 Hz, for changes in pO 2 of 20 mmHg or less (Vikram et al 2008)).…”

“…The speed of responses to changes in pO 2 can be measured with greater accuracy using audio speaker-mediated pressure modulation, as previously described (Vikram et al 2008). This system produces very rapid and controllable fluctuations in pO 2 (on the order of 200 Hz, for changes in pO 2 of 20 mmHg or less (Vikram et al 2008)).…”

“…The temporal responsiveness of LiNc-BuO:PDMS to changes in pO 2 was tested in two ways: by switching the bulk gas (flowing past the sample) from room air to nitrogen and also by inducing rapid fluctuations in oxygen partial pressure using an oscillator-driven speaker-diaphragm setup as reported (Vikram et al 2008). …”

“…Samples were also subjected to sinusoidal changes in pO 2 at frequencies up to 300 Hz, using a previously described speaker-diaphragm apparatus (Vikram et al 2008). In brief, a function generator was used to drive a speaker, the center cone of which was attached to a piston.…”

“…The spatial displacement of the diaphragm due to the movement of the piston by the speaker cone induced a change in volume in the closed system, and, therefore, changed system pO 2 . EPR acquisition and data analysis were performed as described (Vikram et al 2008). …”