Reduced graphene oxide‐based sensing platform for electric cell–substrate impedance sensing

Abstract

Graphene, with its unique electrical properties and biocompatibility, has become a material of choice for the development of biosensor platforms. In this study, a microelectrode array based on reduced graphene oxide (rGO) was constructed and used as a platform for electrical monitoring of cell-substrate adhesion. The rGO-based sensor arrays were designed in order to facilitate sensor pads comparable to the size of individual cells. The sensor chips were fabricated in a scalable manner via site-specific immobilization of graphene oxide flakes onto microelectrode pairs followed by reduction to rGO. The sensor chips were mounted on a measurement platform equipped with a fluidic cell. Electrical characteristics were recorded and fieldeffect behavior was confirmed. Sensors reacted to changes of pH value in the solution. Finally, as a proof-of-concept, the graphene oxide-based sensing platform was used for electrical cell-substrate impedance sensing of individual HEK293 cells in culture.Schematic view of the rGO-based sensor chip for electrical cell-substrate adhesion assays.

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“…Here, it is also interesting to notice a diagonal line appearing on the right side of the Nyquist plot for the devices annealed for 40 s which generally appears due to ionic diffusion in the circuit. However, this is not observed in the subsequent curves and the imepedance behavior suggests for a regular RC equivalent circuit as was observed for the rGO devices in our previous work [26]. A rapid thermal annealing treatment of the GrO chips at 600 8C improved their conductivity by at least three orders of magnitude or more.…”

“…Differently annealed GrO devices, i.e., with different annealing periods were characterized using electrochemical impedance spectroscopy. An electrochemical setup as described in our previous work was used with an external Ag/AgCl reference electrode . A phosphate buffer solution with a value of pH 7 was used as a medium for the electrochemical measurements setup.…”

“…After centrifugation, the supernatant was removed (approximately 250 μl) and replaced by 100 μl of deionized water. The design and configuration of the microelectrodes on our glass chips were discussed in our previous work . Each of the GrO chip contained 16 sensor arrays with typical channel lengths of 5 μm between the source and drain electrodes.…”

“…The hydrophilic nature of the chemical groups present on the GO surfaces enables their easy deployment into different micro‐structuring and micromanipulation techniques. Simple and routine methods for the fabrication of microarray devices and ion‐sensitive field‐effect transistors based on rGO as well as their deployment as biosensors for cell‐substrate adhesion have been previously demonstrated by our group . The fabrication of rGO devices by definition involves processes for the conversion of chemically exfoliated GO into graphene, meaning: (i) getting rid of the oxidative groups on the GO surface and (ii) restoration of the graphene lattice by inducing the formation of sp 2 bonds between adjacent carbon atoms.…”

“…In this paper, the concept for the use of graphite oxide (GrO) multilayers as a suitable material for the fabrication of electronic devices is put forward. The method for the fabrication of GrO electronic devices starts with the exfoliation of GrO multilayers in an optimized chemical procedure which is explained in detail in a recent publication from our group . The GrO flakes are then site‐specifically deposited by using routine dielectrophoretic methods onto microelectrode pairs constituting source and drain electrodes of the electrical device.…”