All-diamond Transistor Array for the Detection of Cell Action Potentials

In an effort towards neuro-prostheses for medical applications and in the quest to understand the fundamental nature of neuronal networks, cellsemiconductor interfaces have been realized in the last decades. The overwhelming majority of the reports used established silicon technology. However, the use of silicon has serious drawbacks like drift and long term degradation. Therefore, materials better suited for the operation in physiological environments are required. Diamond is such a material, with extraordinary properties regarding chemical and electrochemical stability and promising biocompatibility as an all-carbon material. Here we report the first recordings of cell action potentials using readily processed all-diamond transistor arrays. The transistor array presented here is based on undoped hydrogen-terminated single crystalline diamond, which exhibits p-type surface conductivity. This surface conductivity is caused by upward bending of the valence band directly beneath the surface of hydrogen-terminated diamond. Using the diamond as an electrode in an electrolyte, this conductivity is modulated with the electrodes' potential, thereby allowing the design of solution gate field effect transistors (SGFETs). We confirm that this design is stable in relevant physiological environments. Furthermore, the electric characterization shows that the diamond SGFETs are suitable for the detection of cell action potentials regarding the available potential range, the achievable time resolution, and the noise. Culturing HL-1 cells on an array of transistors, we observe a healthy growth on the encapsulation as well as the active gate areas. Recordings of the drain-source current reveal clear, coordinated peaks which are attributed to the action potentials of the HL-1 cells. The shape of the signals can be explained by capacitive and ionic currents, according to the point contact model for the transistor/cell interface. Further experiments with a second cell type, HEK 293 cells, showed healthy growth of individual cells on the active areas of the transistors. Using the patch clamp method we could observe controlled response of the cells and the corresponding signal produced in the transistor. The ionic nature of the cell response is observed via the ion sensitivity of the diamond surface. In summary, the hydrogen-terminated diamond/electrolyte interface is presented as a promising new tool for fundamental research on neuronal networks as well as for application in medical prosthesis.