ConspectusBiointerfacing electrodes have been broadly applied for noninvasively monitoring and modulating neuro-electrical signals, which are of crucial importance in cognition study. Considering that neuro-electrical signals are extremely weak (∼μV scale for electroencephalogram), susceptible to interference and spatiotemporally dependent, there is a pressing need for the development of biointerfacing electrodes with an efficient and stable bioelectronic interface, superior electron-ion transduction, and high spatiotemporal resolution. Although metals and conductive polymers have been used as biointerfacing electrodes, metal electrodes have only electronic conduction properties and a relatively large Young's modulus, while conductive polymer-based hydrogels mainly have ionic conductivity and lack efficient charge transfer ability. Therefore, there is an urgent need for novel biointerfacing electrodes for high-precision, spatiotemporal, and multimodal acquisition of neuro-electrical signals for cognition study. Carbon-based materials, such as graphene and transition metal carbides, exhibiting excellent optoelectrical properties and wide electrochemical stability windows, represent promising candidates. They can be mechanically conformable to the skin and endow the electrodes with electron-ion dual conductivity through synergistic effects with polymers. Their unique physicochemical structures potentially contribute to both efficient and stable bioelectronic interfaces and high spatiotemporal resolution in signal acquisition. In this Account, we summarize recent efforts in the design and fabrication of ultraconformal carbon-based biointerfacing electrodes for cognition study. Regarding the characteristics of neuro-electrical signals for cognition study, we focus on highly conductive graphene and transition metal carbides, and use atomic structure design and polymer interfacing strategies to fabricate biointerfacing electrodes with efficient charge transfer and ultraconformable properties. First, the structurally tunable and diverse carbon-based material systems provide a platform for efficient coupling with underlying biological tissues/organs, enabling an understanding of the relationship between charge coupling mechanisms and carbon material structures. Second, high-density, high-throughput acquisition of neuro-electrical signals in limited space is a key goal in cognition study. Our developed UV-sensitive carbon/polymer composites are compatible with traditional photolithography for the fabrication of biointerfacing electrode arrays. Laser-patterned carbon-based biointerfacing electrode array technology also offers new opportunities for large-scale high-density array production. Furthermore, we introduce an ultrathin "skin-like" bionic substrate with stretchability and adhesiveness, firmly bonded to carbon-based materials via interfacial engineering. The resultant biosensors are capable of high-fidelity, high-resolution, multimodal acquisition of neuro-electrical signals for cognition study. Finally, we outline the design principles for carbon-based biointerfacing electrodes, analyze the technical limitations, and propose future directions for ultraconformal carbon-based bioelectronics.
Hu et al. (Tue,) studied this question.