Carbon Nanotube Transistor Controlled by a Biological Ion Pump Gate Shih-Chieh J. Huang, †,‡ Alexander B. Artyukhin, †,§,¶ Nipun Misra, †,| Julio A. Martinez, †,§ Pieter A. Stroeve, § Costas P. Grigoropoulos, | Jiann-Wen W. Ju, ‡ and Aleksandr Noy* ,†,⊥ † Molecular Biophysics and Functional Nanostructures Group, Physical and Life Sciences Directorate, Lawrence Livermore National Laboratory, Livermore, CA, ‡ Department of Civil Engineering, University of California Los Angeles, Los Angeles, CA, § Department of Chemical Engineering and Materials Science, University of California Davis, Davis, CA, | University of California Berkeley, Berkeley, CA, and ⊥ School of Natural Sciences, University of California Merced, Merced, CA ABSTRACT We report a hybrid bionanoelectronic transistor that has a local ATP-powered protein gate. ATP-dependent activity of a membrane ion pump, Na + /K + -ATPase, embedded in a lipid membrane covering the carbon nanotube, modulates the transistor output current by up to 40%. The ion pump gates the device by shifting the pH of the water layer between the lipid bilayer and nanotube surface. This transistor is a versatile bionanoelectronic platform that can incorporate other membrane proteins. KEYWORDS Nanobioelectronics, carbon nanotube, lipid bilayer, membrane protein, ion pump B iological systems have evolved to perform highly sophisticated tasks. To achieve that complexity, liv- ing organisms rely on protein machines that store and transmit information, 1,2 shuttle ions and molecules in and out of the cell, 3 and perform other essential duties. Great precision, efficiency, and accuracy of these biomolecules make them an attractive choice for incorporation into artificial hybrid circuits to introduce new functionality and improve device performance. 4,5 Carbon nanotube (CNT) devices are particularly promising candidates for building an inorganic platform for electronic integration of biomolecules given their ability to operate in physiological conditions, high sensitivity, and size scale suitable for working with individual proteins. 6 At the same time, hydrophobic CNT surfaces do not represent a natural environment for most biomolecules and often have strong nonspecific interactions with pro- teins. 7 We and others have recently developed an approach for integrating biological molecules with carbon nanotube devices that is based on coating the CNTs with lipid bilayers. 8,9 In these devices, the lipid bilayer performs two key roles: it serves as an impenetrable barrier between the CNT and the surrounding medium turning it from a “bare” wire into a “shielded” wire, and it also serves as a matrix for membrane proteins. In this work, we have exploited these two key advantages to demonstrate a bionanoelec- tronic device that uses a protein machine, Na + /K + -ATPase, powered by ATP hydrolysis, to control the output of a carbon nanotube transistor. The Na + /K + -ATPase is an ion trans- porter protein found in virtually all eukaryotic cells; 3,10 its function is to control and maintain sodium and potassium ion gradients and osmotic pressure across the plasma mem- brane. 11 This protein metabolizes ATP to undergo a cycle of conformational changes 11,12 that translocates three Na + ions and two K + ions in opposite directions across the membrane with the net result of accumulating an extra cation at the extracellular side of the membrane (the side opposite to the ATP hydrolysis site). Specificity in controlling ionic gradients, 11 simple reconstitution, 13 and abundance in nature make Na + /K + -ATPase an attractive component for use in nanoelectronic devices. Several previous studies have integrated proteins with nanotube or nanowire electronic devices. 9,14 However, these devices incorporated passive biological elements, which transmitted an environmental change to the nanowire using molecular recognition, 9 or equilibrium ion transport. 14 Our work demonstrates the possibility of using an ATP-powered biological machine to control a nanoelectronic circuit. Our experiments used a carbon nanotube transistor platform (Figure 1a, also see Supporting Information for more details) in which a single semiconducting single-walled carbon nanotube bridged two metal electrodes that served as transistor’s source and drain (Figure 1a,b). The source and drain electrodes were insulated from the solution by an additional coating with LOR3A photoresist that left only the middle section of the CNT exposed to the solution. This modification not only improved the signal-to-noise ratio but also eliminated any contribution from the nanotube-elec- trode contacts. 15 We used vesicle fusion to coat the device surface with a lipid bilayer (DPhPC/DPhPE/PI/Cholesterol 61/ 14.4/2.6/22 by weight, see Supporting Information for de- * To whom correspondence should be addressed. E-mail: anoy@ucmerced.edu; anoy@lbl.gov. ¶ Current address: Department of Molecular Biology, University of Texas South- western Medical Center, Dallas, TX Received for review: 2/10/2010 Published on Web: 04/28/2010 pubs.acs.org/NanoLett © 2010 American Chemical Society 1812 DOI: 10.1021/nl100499x | Nano Lett. 2010, 10, 1812–1816