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We report on a comparison of different gate oxides for AlGaN/GaN highelectron-mobility transistor (HEMT) pH sensors. The HEMTs show a linear increase in drain-source current as the pH of the electrolyte solutions introduced to the gate region is decreased. Three different gate oxides were examined, namely the native oxide on the AlGaN surface, a UV-ozone-induced oxide and an Sc 2 O 3 gate deposited by molecular beam epitaxy. The Sc 2 O 3 produced superior results in terms of resolution in measuring small changes in pH. The devices with Sc 2 O 3 in the gate region exhibited a linear change in current between pH 3 and 10 of 37 lA/pH with a resolution of <0.1 pH over the entire pH range. In contrast, the native oxide devices showed a larger change in current, $70 lA/pH, but with a degraded resolution of $0.4 pH. Results for the UV-ozone oxide were intermediate in resolution, 0.2 pH. These HEMTs have promise for detecting pH changes in biological samples and can be readily integrated into a standard package for wireless data transmission.

Exercise is known to promote mitochondrial biogenesis in skeletal muscle as well as enhance mitochondrial function and efficiency in human and rodent models. These adaptations help to decrease exercise-associated production of reactive oxygen species, which can negatively affect health and performance if antioxidant mechanisms are overwhelmed. Little is known about the adaptations of mitochondria in response to exercise training in the growing horse or if supplementation with a dietary antioxidant can improve mitochondrial function. To evaluate the separate and combined effects of selenium (Se) supplementation, training, and an acute strenuous exercise bout on mitochondrial adaptations in young horses, 30 American Quarter Horse yearlings were randomly assigned to an exercise training group or a no-training group and, within each group, received either 0.1 or 0.3 mg Se/kg DM for 14 wk. The study was split into 2 phases (wk 0 to 8 and wk 9 to 14), with half of the trained horses switched to the opposite dietary treatment in Phase 2. At the end of each phase, all horses underwent a 120-min submaximal exercise test (SET; SET 1 and SET 2). Biopsies of the middle gluteal muscle were collected before and after each phase of the study and in response to each SET and analyzed for markers of mitochondrial number and function. At rest, horses receiving 0.3 mg Se/kg DM had higher citrate synthase activity ( = 0.021) than horses receiving 0.1 mg Se/kg DM, indicating higher mitochondrial content. In contrast, cytochrome oxidase (CCO) activity was not affected by dietary Se overall, but horses that were dropped from 0.3 mg Se/kg DM to 0.1 mg Se/kg DM during Phase 2 showed a decrease ( = 0.034) in integrated CCO activity from wk 9 to 14, suggesting impaired mitochondrial function. Mitochondrial enzyme activities were unaffected by an acute, strenuous exercise bout (SET 1 and SET 2). Our relatively low-intensity exercise training protocol did not appear to induce functional mitochondrial adaptations. However, elevated dietary Se may impart beneficial effects on mitochondrial biogenesis during growth and training. A more strenuous exercise training protocol should be investigated to determine the potential benefits of elevated dietary Se for elite equine athletes.

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