The authors describe mitochondrial studies in a 6-year-old patient with a seizure disorder that can be seen in myoclonic epilepsy and ragged red fibers. Using a recently developed noninvasive approach, analysis of buccal mitochondrial enzyme function revealed severe respiratory complex I and IV deficiencies in the patient. In addition, analysis of buccal mitochondrial DNA showed significant amounts of the common 5 kb and 7.4 kb mitochondrial DNA deletions, also detectable in blood. This study suggests that a buccal swab approach can be used to informatively examine mitochondrial dysfunction in children with seizures and may be applicable to screening mitochondrial disease with other clinical presentations.

Resolving low-energy features in the density of states (DOS) holds the key to understanding a wide variety of rich novel phenomena in graphene-based 2D heterostructures. The Lifshitz transition in bilayer graphene (BLG) arising from trigonal warping has been established theoretically and experimentally. Nevertheless, the experimental realization of its effects on transport properties has been challenging because of its relatively low energy scale (∼1 meV). In this work, we demonstrate that the thermoelectric power (TEP) can be used as an effective probe to investigate fine changes in the DOS of BLG. We observed additional entropy features in the vicinity of the charge neutrality point (CNP) in gapped BLG. This apparent violation of the Mott formula can be explained quantitatively by considering the effects of trigonal warping, thereby serving as possible evidence of a Lifshitz transition.

The combination of field-tunable bandgap, topological edge states, and valleys in the band structure, makes insulating bilayer graphene a unique localized system, where the scaling laws of dimensionless conductance g remain largely unexplored. Here we show that the relative fluctuations in ln g with the varying chemical potential, in strongly insulating bilayer graphene (BLG) decay nearly logarithmically for channel length up to L/ξ ≈ 20, where ξ is the localization length. This 'marginal' self-averaging, and the corresponding dependence of ln g on L, suggest that transport in strongly gapped BLG occurs along strictly one-dimensional channels, where ξ ≈ 0.5±0.1 µm was found to be much longer than that expected from the bulk bandgap. Our experiment reveals a nontrivial localization mechanism in gapped BLG, governed by transport along robust edge modes.

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