Highly Sensitive and Wearable In 2 O 3 Nanoribbon Transistor Biosensors with Integrated On-Chip Gate for Glucose Monitoring in Body Fluids Qingzhou Liu, † Yihang Liu, ‡ Fanqi Wu, † Xuan Cao, † Zhen Li, ‡ Mervat Alharbi, § Ahmad N. Abbas, ∥,⊥ Moh R. Amer,* ,§,# and Chongwu Zhou* ,†,‡ † Mork Family Department of Chemical Engineering and Materials Science and ‡ Ming Hsieh Department of Electrical Engineering, University of Southern California, Los Angeles, California 90089, United States § Center of Excellence for Green Nanotechnologies, Joint Centers of Excellence Program, King Abdulaziz City for Science and Technology, P.O Box 6086, Riyadh 11442, Saudi Arabia ∥ Department of Electrical and Computer Engineering, University of Jeddah, 285 Dhahban 23881, Saudi Arabia ⊥ Department of Electrical and Computer Engineering, King Abdulaziz University, Abdullah Sulayman Street, Jeddah 22254, Saudi Arabia # Department of Electrical Engineering, University of California, Los Angeles, 420 Westwood Plaza, 5412 Boelter Hall, Los Angeles, California 90095, United States * S Supporting Information ABSTRACT: Nanoribbon- and nanowire-based field-effect transistor (FET) biosensors have stimulated a lot of interest. However, most FET biosensors were achieved by using bulky Ag/AgCl electrodes or metal wire gates, which have prevented the biosensors from becoming truly wearable. Here, we demonstrate highly sensitive and conformal In 2 O 3 nanoribbon FET biosensors with a fully integrated on-chip gold side gate, which have been laminated onto various surfaces, such as artificial arms and watches, and have enabled glucose detection in various body fluids, such as sweat and saliva. The shadow-mask-fabricated devices show good electrical performance with gate voltage applied using a gold side gate electrode and through an aqueous electrolyte. The resulting transistors show mobilities of ∼22 cm 2 V −1 s −1 in 0.1× phosphate-buffered saline, a high on−off ratio (10 5 ), and good mechanical robustness. With the electrodes functionalized with glucose oxidase, chitosan, and single-walled carbon nanotubes, the glucose sensors show a very wide detection range spanning at least 5 orders of magnitude and a detection limit down to 10 nM. Therefore, our high- performance In 2 O 3 nanoribbon sensing platform has great potential to work as indispensable components for wearable healthcare electronics. KEYWORDS: wearable biosensor, gold side gate, glucose sensor, indium oxide semiconductor, field-effect transistor, shadow-mask fabrication W earable biosensors are smart electronic devices that can be worn on the body as implants or accessories. Recent advances in microelectronics, telecommuni- cations, and sensor manufacturing have opened up possibilities for using wearable biosensors to continuously monitor an individual’s body status without interrupting or limiting the user’s motions. 1−8 However, while many commercially available wearable electronics can track users’ physical activities, devices that can provide an insightful view of user’s health status at the molecular level need more development. On the other hand, although some commercial hand-held analyzers enable glucose or lactate detection, most of these devices rely on blood samples. 9 Neither finger-prick nor invasive sensors (such as a needle embedded under the skin) are desired for wearable biomedical applications. Continuous analyte monitoring, a key advantage offered by wearable biosensors, has great potential in Received: September 25, 2017 Accepted: December 19, 2017 Article www.acsnano.org Cite This: ACS Nano XXXX, XXX, XXX-XXX © XXXX American Chemical Society A DOI: 10.1021/acsnano.7b06823 ACS Nano XXXX, XXX, XXX−XXX