Graphene quantum dots (GQDs) are a promising next generation nanomaterial with manifold biomedical applications. For real world applications, comprehensive studies on their influence on the functionality of primary human cells are mandatory. Here, we report the effects of GQDs on the transcriptome of CD34 + hematopoietic stem cells after an incubation time of 36 hours. Of the 20 800 recorded gene expressions, only one, namely the selenoprotein W, 1, is changed by the GQDs in direct comparison to CD34 + hematopoietic stem cells cultivated without GQDs. Only a meta analysis reveals that the expression of 1171 genes is weakly affected, taking into account the more prominent changes just by the cell culture. Eight corresponding, weakly affected signaling pathways are identified, which include, but are not limited to, the triggering of apoptosis. These results suggest that GQDs with sizes in the range of a few nanometers hardly influence the CD34 + cells on the transcriptome level after 36 h of incubation, thereby demonstrating their high usability for in vivo studies, such as fluorescence labeling or delivery protocols, without strong effects on the functional status of the cells.

Human leukocytes obtained from samples of leukapheresis products of three healthy donors stimulated by granulocyte colony stimulating factor (G-CSF) were exposed to graphene quantum dots. A time-and concentration dependent uptake was observed with a significantly greater uptake into monocytes and granulocytes in comparison to lymphocytes, suggesting a better incorporation ability of cells with phagocytotic properties. The uptake rates also correlate with the cell membrane area. Looking at the different lymphoid subsets a greater uptake was found into CD19 + B-, CD56 + natural killer cells and CD34 + hematopoietic stem cells (HSC) in comparison to CD4 + T-and CD8 + T cells. Independent of the cell type studied, the observed uptake dynamics is consistent with a diffusion-driven process, which allows the determination of cell-specific membrane permeabilities for the graphene quantum dots. The toxicity of the quantum dots is relatively low resulting in a 90% viability of the entire leukocyte population after 36 hours of exposure to GQDs at a concentration of 500 mg ml À1 .

Among various nanoparticles tested for pharmacological applications over the recent years, graphene quantum dots (GQDs) seem to be promising candidates for the construction of drug delivery systems due to their superior biophysical and biochemical properties. The subcellular fate of incorporated nanomaterial is decisive for transporting pharmaceuticals into target cells. Therefore a detailed characterization of the uptake of GQDs into different breast cancer models was performed. The demonstrated accumulation inside the endolysosomal system might be the reason for the particles’ low toxicity, but has to be overcome for cytosolic or nuclear drug delivery. Furthermore, the penetration of GQDs into precision-cut mammary tumor slices was studied. These constitute a far closer to reality model system than monoclonal cell lines. The constant uptake into the depth of the tissue slices underlines the systems’ potential for drug delivery into solid tumors.

Hybrid lateral superlattices composed of a square array of antidots and a periodic one-dimensional magnetic modulation are prepared in Ga [Al]As heterostructures. The two-dimensional electron gases exposed to these superlattices are characterized by magnetotransport experiments in vanishing average perpendicular magnetic fields. Despite the absence of closed orbits, the diagonal magnetoresistivity in the direction perpendicular to the magnetic modulation shows pronounced classical resonances. They are located at magnetic fields where snake trajectories exist which are quasi-commensurate with the antidot lattice. The diagonal magnetoresistivity in the direction of the magnetic modulation increases sharply above a threshold magnetic field and shows no fine structure. The experimental results are interpreted with the help of numerical simulations based on the semiclassical Kubo model. PACS numbers: 73.23.-b, 73.63.-b z , which allows a more direct comparison to the simulations. Even though the simulated function ρ xx (B max z ) deviates from the experimental trace in several aspects, the most prominent features are reproduced qualitatively, namely the positive magnetoresistivity around B max z = 0, minima close to B max z = 53 mT, 110 mT, 170 mT and 280 mT, the decrease of ρ xx at B max z ≈ 260 mT, and some weakly pronounced maxima and minima at larger magnetic fields. The sharp decrease of of ρ xx around B max z = 500 mT is not observed experimentally, most likely because our fringe fields are too weak. The simulation of ρ yy (B max z) is compared to the scaled experimental data in Fig. 3 (c). Very good agreement is found for B max z ≤ 0.3 T, while the strong increase of the resistivity around B max z ≈ 0.4 T is reproduced as well, though shifted to slightly higher magnetic fields. Further simulations 30 show that the presence of the antidots does influence ρ yy (B max z ) to some extent, but the overall behavior is dominated by the magnetic barriers and is not an effect of the hybrid superlattice.We proceed by interpreting the magnetoresistivity features in terms of the electron dynamics which determines the components of the magnetoconductivity tensor. 30 The off-diagonal elements σ xy and σ yx are approximately independent of B max z and of the order of 0.1 mS. σ yy decreases from 18 mS at B max z = 0 to almost zero at B max z ≈ 0.5 T. Only σ xx shows resonances as B max z is changed. This implies that ρ xx ≈ 1/σ xx and ρ yy ≈ 1/σ yy , while ρ xy (B y ) ≈ σ xy /(σ xx σ yy ). The sharp increase of ρ xy (see Ref. 30) and ρ yy at B max z = 0.5 T has thus its origin in the strongly suppressed diagonal conductivity in y-direction.FIG. 4. (color online). Poincaré sections for various values of B max z (a-e). Some characteristic trajectories are shown in (f), the initial conditions of which are indicated by full circles in the corresponding Poincaré sections.