Short Communication
A flexible hydrophilic-modified graphene microprobe for neural and cardiac recording

https://doi.org/10.1016/j.nano.2012.12.004Get rights and content

Abstract

A graphene-based flexible microprobe developed by microelectromechanical system technology shows high resolution for the detection of electrophysiological signals from various bio-objects. The hydrophilization post-treatment using steam plasma was performed on the graphene surface to decrease the interfacial impedance between graphene and electrolyte, and thus improve the signal-to-noise ratio during neural and cardiac recording. The signal-to-noise ratio of the action potentials from axons of a crayfish measured by hydrophilic-modified graphene microprobe (27.8 ± 4.0 dB) is higher than that of untreated device (20.3 ± 3.3 dB). Also, the form of the QRS complex and T wave in the electrocardiogram of the zebrafish heart can be clearly distinguished using the modified device. The total measured noise levels of the overall stability of the system were 4.2 μVrms (hydrophilic graphene) and 7.64 μVrms (hydrophobic graphene). The graphene-based implant can be further used for in vivo, long-term recording and retina prosthesis.

From the Clinical Editor

In this study a graphene-based flexible microprobe developed using microelectromechanical system technology was demonstrated to enable high resolution detection of electrophysiological signals, including EKG in zebrafish models. Both hydrophilic and hydrophobic graphene were studied, paving the way to potential future clinical applications of this new technology.

Section snippets

Methods

Fig. 1A shows our design of a novel prototype neural interface using graphene as an electrode and SU-8 as a flexible substrate; SU-8 provides satisfactory biocompatibility, effective electrical insulation, and great flexibility, but one issue for graphene materials is their intrinsically great hydrophobicity, which might lead to a large impedance between graphene and an electrolyte surface. We demonstrate that a graphene surface with a mild steam plasma (SP) significantly increases the

Results

The CVD graphene as-grown of average contact angle was 91.1° ± 5.6° (hydrophobic). The surface of graphene treated at 25 W for 1-s SP was 41° ± 4.7° (hydrophilic) (Fig. S2). Fig. 2A shows our measurement of the spontaneous action potentials (AP) from the axons that run along the abdominal nerve cord of crayfish to confirm the functionality of the microprobe based on graphene. The axons link two ganglions. The spontaneous AP from the axons between the second and third abdominal ganglions were

Discussion

We have demonstrated that the detection of neural and electrocardiographic recording can be carried out by using a graphene-based flexible microprobe. The effect of the SP treatment demonstrates the surface wettability of graphene, the average contact angle decreased from 91.1° ± 5.6° to 41° ± 4.7° (Fig. S2). With the hydrophilic graphene, it becomes feasible to separate electrophysiological signals and to recognize their distinct shapes. The results also show that the electrode yields a larger

Acknowledgments

We thank Professor Fan-Gang Tseng of National Tsing Hua University for providing the fabrication facilities and impedance measurements.

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National Science Council of Republic of China (Taiwan) provided partial support through grant NSC 96-2627-E-007-002. Graphene synthesis and characterization were supported by Academia Sincia, Taiwan.

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