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 .

This study reports on the development of vertical, partially encapsulated nanoelectrodes for electrically contacting the interior of electrogenic cells with microelectronics. Intracellular electrical stimulation and recording with single cell resolution enables new insights into the electrophysiology of cells embedded in a complex multicellular network, providing detailed understanding of fundamental processes affecting cell to cell communication and thereby paving the way for novel applications including pharmacological studies and other neuromodulation techniques like focused ultrasound and electroceuticals. In order to minimize the influence of the measurement system, an approach based on nano-sized hollow electrodes, achieving an adhesion based intracellular access, is used. The focus of the presented work is on the novel fabrication technology and the characterization of the resulting nanoelectrodes. In CMOS compatible processes, the hollow geometry is achieved using a sacrificial layer technique combining deep reactive ion etching and atomic layer deposition of Ru. For decoupling the extracellular milieu, a partial passivation of the nanoelectrodes by Ta 2 O 5 is realized. The monolithic integration allows an application specific fine-tuning of geometry and placement of the nanoelectrodes. A discrete microelectrode array was designed to electrically and electrochemically characterize the nanoelectrodes. Resistance measurements, cyclic voltammetry and electrochemical impedance spectroscopy show the feasibility of the developed electrodes as an electronic interface to electrochemical fluids. Specifically, an electrode resistance of 2.92 k and charge delivery capacitance of 748.13 μC cm 2 were observed. Confocal microscopy analyses of neural cells interfaced with the nanoelectrodes indicate an adhesion based intracellular access as well as biostability and biocompatibility.

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