Micro-sized microbial fuel cells (MFCs) are miniature energy harvesters that use bacteria to convert biomass from liquids into usable power. The key challenge is transitioning laboratory test beds into devices capable of producing high power using readily available fuel sources. Here, we present a pragmatic step toward advancing MFC applications through the fabrication of a uniquely mobile and inexpensive micro-sized device that can be fueled with human saliva. The 25-ll MFC was fabricated with graphene, a two-dimensional atomic crystal-structured material, as an anode for efficient current generation and with an air cathode for enabling the use of the oxygen present in air, making its operation completely mobile and free of the need for laboratory chemicals. With saliva as a fuel, the device produced higher current densities (1190 A m À3 ) than any previous aircathode micro-sized MFCs. The use of the graphene anode generated 40 times more power than that possible using a carbon cloth anode. Additional tests were performed using acetate, a conventional organic material, at high organic loadings that were comparable to those in saliva, and the results demonstrated a linear relationship between the organic loading and current. These findings open the door to saliva-powered applications of this fuel cell technology for Lab-on-a-Chip devices or portable point-of-care diagnostic devices.

Utilization of graphene may help realize innovative low-power replacements for III-V materials based high electron mobility transistors while extending operational frequencies closer to the THz regime for superior wireless communications, imaging, and other novel applications. Device architectures explored to date suffer a fundamental performance roadblock due to lack of compatible deposition techniques for nanometer-scale dielectrics required to efficiently modulate graphene transconductance (gm) while maintaining low gate capacitance-voltage product (CgsVgs). Here we show integration of a scaled (10 nm) high-κ gate dielectric aluminum oxide (Al2O3) with an atmospheric pressure chemical vapor deposition (APCVD)-derived graphene channel composed of multiple 0.25 μm stripes to repeatedly realize room-temperature mobility of 11,000 cm(2)/V·s or higher. This high performance is attributed to the APCVD graphene growth quality, excellent interfacial properties of the gate dielectric, conductivity enhancement in the graphene stripes due to low tox/Wgraphene ratio, and scaled high-κ dielectric gate modulation of carrier density allowing full actuation of the device with only ±1 V applied bias. The superior drive current and conductance at Vdd = 1 V compared to other top-gated devices requiring undesirable seed (such as aluminum and poly vinyl alcohol)-assisted dielectric deposition, bottom gate devices requiring excessive gate voltage for actuation, or monolithic (nonstriped) channels suggest that this facile transistor structure provides critical insight toward future device design and process integration to maximize CVD-based graphene transistor performance.

Microbial fuel cells harvest electrical energy produced by bacteria during the natural decomposition of organic matter. We report a micrometer‐sized microbial fuel cell that is able to generate nanowatt‐scale power from microliters of liquids. The sustainable design is comprised of a graphene anode, an air cathode, and a polymer‐based substrate platform for flexibility. The graphene layer was grown on a nickel thin film by using chemical vapor deposition at atmospheric pressure. Our demonstration provides a low‐cost option to generate useful power for lab‐on‐chip applications and could be promising to rapidly screen and scale up microbial fuel cells for water purification without consuming excessive power (unlike other water treatment technologies).

1 Introduction Wide band gap semiconductors like gallium nitride (GaN) and silicon carbide (SiC) are currently employed in high temperature power transistor applications owing to their superior combination of characteristics including mobility, breakdown voltage, cutoff frequency, and operating temperature [1]. However, fabricating these devices using high vacuum epitaxial growth techniques (i.e. molecular beam epitaxy, MBE or metal organic chemical vapor deposition, MOCVD) is often cost prohibitive. Recently, high mobility graphene transistors have exhibited cut-off frequencies in the GHz regime suggesting that they are promising candidate for future low cost RF electronic applications [2]. However, the behavior of graphene devices needs to be evaluated at elevated temperatures in order to understand its behavior for harsh environment applications. The technique used in this study, APCVD, has emerged as both a cheap and scalable approach to graphene synthesis. Apart from the consideration of industrial applications, a great portion of CVD derived graphene studies have reported on graphene's growth mechanism [3,4], electronic properties [5][6][7], substrate interface [8,9] and device fabrication issues [10,11]. However, the lack of studying CVD based graphene functionality at elevated temperatures is a roadblock to realize low cost CVD graphene devices for use in high temperature

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