Fig. 5.

Temporal response of LiNc-BuO:PDMS chip to changes in oxygen partial pressure. Effect of oxygenation/deoxygenation on the EPR response of LiNc-BuO:PDMS was measured at X-band (9.8 GHz). Chips made by the encapsulation of 40 mg of LiNc-BuO in 5.5 g of PDMS were used, while uncoated LiNc-BuO was used as a standard for comparison. The samples were equilibrated with nitrogen and the magnetic field was set at the peak of the EPR spectrum under anoxic condition (preset). The response of the EPR signal to rapid switching of the perfusing gas, from nitrogen (0% O₂) to room air (20.9% O₂), was monitored and recorded. The time point when room air is introduced is indicated by the filled arrow, while switching to nitrogen is indicated by the clear arrow. The Y-axis of each panel represents the EPR intensity (in arbitrary units) at the preset magnetic field (peak of the anoxic EPR spectrum) (a) Response of uncoated LiNc-BuO. It can be observed that the unencapsulated probe is characterized by rapid switching times (Pandian et al. 2006); of less than a second when switching from nitrogen to room air and approximately 3 seconds when switching from room air back to nitrogen. (b) Response of LiNc-BuO:PDMS chip. The chip response was markedly slower compared to uncoated LiNc-BuO. The switch from nitrogen to room air was relatively fast (~5 s), but the switch from room air to nitrogen took significantly longer (~120 s)