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Jonghyun Choi1 Yongdeok Kim2 Gelson Pagan3 Yerim Kim1 Pilgyu Kang1 Rashid Bashir4 3 SungWoo Nam1 2

1, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States
2, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States
3, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States
4, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States

Nanomaterials offer promising platforms for establishing active interface with biological systems, owing to their unique electrical, optical, mechanical properties and large surface-to-volume ratio. Among various nanomaterials-based bioelectronic platforms, graphene has been shown to be an advanced building block over zero- and one-dimensional nanomaterials, owing to its compatibility with conventional top-down approaches (for scalable and low-cost process), high carrier mobility (i.e., sensitivity), and the complementary field-effect sensing capability (both at the p- and n-type regimes). Thus, a variety of graphene-based bioelectronic studies have been reported, such as the electrical recording of electrogenic cells (e.g., cardiac muscle cells). However, little work has been reported beyond other phenotypes, and no studies have demonstrated simultaneous optical stimulation and its electrical and optical recording. In this work, we report light-stimulation of optogenetically encoded mouse-derived skeletal muscle cell lines (C2C12) and their simultaneous imaging and electrical recording based on optically transparent graphene field-effect transistors (FETs). C2C12 transfected with channelrhodopsin-2 (ChR2) was used to express ChR2, and the transparent graphene FET array was prepared by the deposition of graphene on quartz followed by the standard photolithography processes. The light-stimulation with various frequencies (0.5 to 4.0 Hz) and pulse-widths (50 to 500 ms) generated reproducible contractions of the differentiated ChR2-expressing C2C12, which was recorded by the video as well as the biphasic current signals both at the p- and n-type regimes of graphene FET. Control experiments without cells showed no biphasic current peaks under the light-stimulation, demonstrating the current signals resulted from the myogenic action potentials instead of the photoresponse of graphene. Our work, for the first time, demonstrates electrical measurements of optically stimulated skeletal muscle cells based on optically transparent graphene FETs. The distinct and complementary properties of transparent graphene FET and its versatile sensing capabilities will open up unique opportunities in the field of nano-bioelectronics and electrophysiology in the future.

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