We investigate the effect of surface termination on the charge state of nitrogen vacancy centers, which have been ion-implanted few nanometers below the surface of diamond. We find that, when changing the surface termination from oxygen to hydrogen, previously stable NV − centers convert into NV 0 and, subsequently, into an unknown non-fluorescent state. This effect is found to depend strongly on the implantation dose. Simulations of the electronic band structure confirm the dissappearance of NV − in the vicinity of the hydrogen-terminated surface. The band bending, which induces a p-type surface conductive layer leads to a depletion of electrons in the nitrogenvacancies close to the surface. Therefore, hydrogen surface termination provides a chemical way for the control of the charge state of nitrogen-vacancy centers in diamond. Furthermore, it opens the way to an electrostatic control of the charge state with the use of an external gate electrode.

Arrays of graphene solution‐gated field‐effect transistors are fabricated for the detection of electrical activity of electrogenic cells. Cardiomyocyte‐like cells are cultured on the transistor arrays and their action potentials are detected by the underlying transistors. The analysis of the recorded cell signals and the electronic noise of the transistors confirm that graphene transistors surpass state‐of‐the‐art devices for bioelectronic applications.

The nitrogen-vacancy (NV) centre in diamond is a promising candidate for a solid-state qubit. However, its charge state is known to be unstable, discharging from the qubit state NV− into the neutral state NV0 under various circumstances. Here we demonstrate that the charge state can be controlled by an electrolytic gate electrode. This way, single centres can be switched from an unknown non-fluorescent state into the neutral charge state NV0, and the population of an ensemble of centres can be shifted from NV0 to NV−. Numerical simulations confirm the manipulation of the charge state to be induced by the gate-controlled shift of the Fermi level at the diamond surface. This result opens the way to a dynamic control of transitions between charge states and to explore hitherto inaccessible states, such as NV+.