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We report on nanometer magnetic imaging of two-dimensional current flow in bilayer graphene devices at room temperature. By combining dynamical modulation of the source-drain current with ac quantum sensing of a nitrogen-vacancy center in the diamond probe tip, we acquire magnetic field and current density maps with excellent sensitivities of 4.6 nT and 20 nA/μm, respectively. The spatial resolution is 50-100 nm. We introduce a set of methods for increasing the technique's dynamic range and for mitigating undesired back-action of magnetometry operation (scanning tip, laser and microwave pulses) on the electronic transport. Finally, we show that our imaging technique is able to resolve small variations in the current flow pattern in response to changes in the background potential. Our experiments demonstrate the feasibility for detecting and imaging subtle spatial features of nanoscale transport in two-dimensional materials and conductors.

We measure quasiparticle tunneling across a constriction in the first Landau level. In the limit of weak backscattering, the dependence of the tunneling conductance on temperature and dc-bias is in qualitative disagreement with existing theories. For stronger backscattering, data obtained in the ν = 1/3 state can be fitted to weak backscattering theory with the predicted effective fractional charge of e * = e/3. The scaling parameter g is however not universal and depends strongly on the gate voltage applied to the constriction. At ν = 4/3, a more complex picture emerges. We propose an interpretation in terms of selective tunneling between the multiple modes present at the edge.

We report on the implementation of a scanning nitrogen-vacancy (NV) magnetometer in a dry dilution refrigerator. Using pulsed optically detected magnetic resonance combined with efficient microwave delivery through a co-planar waveguide, we reach a base temperature of 350 mK, limited by experimental heat load and thermalization of the probe. We demonstrate scanning NV magnetometry by imaging superconducting vortices in a 50-nm-thin aluminum microstructure. The sensitivity of our measurements is approximately 3  μT per square root Hz. Our work demonstrates the feasibility for performing noninvasive magnetic field imaging with scanning NV centers at sub-Kelvin temperatures.

Novel glycoproteins, inaccessible by other techniques, can be obtained by metabolic engineering of the oligosaccharide biosynthesis pathway. Furthermore, alteration of cell-surface oligosaccharides can change the properties of receptors involved in cell-cell adhesion. Sialyl Lewis X (sLex) is a cell-surface oligosaccharide determinant which is specifically expressed on granulocytes and monocytes and which interacts with selectins to influence leukocyte trafficking, thrombosis, inflammation, and cancer. Antisense technology targeting fucosyltransferase VI (Fuc-TVI), an enzyme necessary for the synthesis of the sLex in engineered Chinese hamster ovary (CHO) cells, has reduced Fuc-TVI activity, sLex synthesis, and adhesion to endothelial cells. Antisense methodology to reduce targeted activity in oligosaccharide biosynthesis or other pathways is an important addition to CHO cell metabolic engineering capabilities.