Carbon Nanotube/Green Tea Composite for the Electronic Detection of Hydrogen Peroxide Yanan Chen, Yang Doo Lee, Harindra Vedala, Brett L. Allen, and Alexander Star * * Department of Chemistry, University of Pittsburgh and the National Energy Technology Laboratory, Pittsburgh, PA 15260, USA, astar@pitt.edu ABSTRACT Single-walled carbon nanotubes (SWNTs) and their composites are ideal candidates for chemical and biological sensing application, due to their unique electronic, chemical and physical properties. Green tea, or more specifically its main antioxidant component, epigallocatechin gallate (EGCG), has been found to disperse SWNTs in water and form SWNT/green tea (SWNT/EGCG) composite. With the presence of EGCG, this SWNT composite should have strong antioxidant properties and thus respond to reactive oxygen species (ROS). Here we report the fabrication and characterization of a SWNT/Green Tea (SWNT/EGCG) sensing system for the detection of H 2 O 2 in solution phase. By liquid-gating field-effect (FET) transistor measurements and conductance measurements, it was observed that the conductance of SWNT/EGCG composite thin film increased with increase in H 2 O 2 concentrations. These findings suggest that SWNT/Green Tea composite has a great potential for developing simple resistivity-based nanoscale sensors for the electronic detection of ROS. Keywords: single-walled carbon nanotubes, antioxidant, resistivity sensors, ROS, hydrogen peroxide 1 INTRODUCTION The determination of hydrogen peroxide is very important, because it is a by-product of many biological processes and an essential mediator in food, pharmaceutical, clinical, industrial and environmental analysis. 1 There have been many demonstrated examples of hydrogen peroxide sensors using various techniques, including spectrometry, 2 chemiluminescence 3 and electrochemistry 4 . However, carbon nonamaterial-based resistivity sensors for hydrogen peroxide have not been fully explored. Here we report a carbon nanotube/green tea (EGCG) composite-based resistivity sensor for the detection of hydrogen peroxide. Single-walled carbon nanotubes (SWNTs) have been of increasing importance in a variety of areas including materials and life sciences. 5-7 Because of their size (approximately 1-3 nm in diameter, 1 µm long) and unique physical and electronic properties, SWNTs are an ideal material to interface with biological systems. Made solely from the leaves of Camellia sinensis, green tea has been extensively studied for its antioxidant abilities. 8 Specifically, antioxidant properties can be derived from the presence of catechins. Catechins are a group of water- soluble polyphenols, consisting of epicatechin (EC), epicatechin gallate (ECG), epigallocatechin (EGC), and epigallocatechin gallate (EGCG). Such compounds possess biological activity exhibiting not only antioxidant behavior, but antitumor and anticancer effects as well. Among antioxidants present in green tea, EGCG is the most abundant and has the strongest activity. 9 This compound reacts readily with reactive oxygen species (ROS) such as superoxide (O 2 - ), hydroxyl radicals (·OH), and hydrogen peroxide (H 2 O 2 ). 10 It has been reported that green tea or EGCG can disperse nanotubes in aqueous solutions and for SWNT/green tea (EGCG) composite. 11 2 RESULTS 2.1 Device Fabrication We obtained the SWNT/EGCG composite (Figure 1a) by sonicating approximately 1 mg of SWNTs in 20 mL of 0.3 mg/mL green tea (or 4×10 -4 M EGCG) at room temperature (Sonicator: Branson 5510) for 1 hr. The solution was then centrifuged (Fisher Scientific centrific model 228) at 3400 RPM for 15 minutes. The supernatant was then filtered and washed with deionized water subsequently to remove any unbound green tea (EGCG). The resulting material was then dispersed in water to obtain SWNT/green tea (SWNT/EGCG) suspension (resulting concentration 0.05 mg/mL). This composite material was characterized by ultraviolet-visible-near-infrared (UV-Vis-NIR) absorption spectroscopy Fourier transform infrared (FTIR) spectroscopy, transmission electron microscopy (TEM), and atomic force microscopy (AFM) in thin films. 12 Spectroscopic measurements were taken of a spray-cast film on a quartz slide using UV-Vis-NIR spectroscopy. The resulting spectrum is a superposition of SWNTs and EGCG spectra (Figure 1b), in a good agreement with previous solution studies. 11 Metal interdigitated devices (Au/Ti, 100 nm/30 nm) with interelectrode spacing of 10 μm were patterned on a Si/SiO 2 substrate using conventional photolithography. One chip (2mm×2mm) containing four identical devices was then set into a 40-pin ceramic dual in-line package (CERDIP) and wire-bonded using Au wire. Devices were subsequently isolated from the rest of the package by epoxying the inner cavity. Fabrication of bare SWNTs conductance measurement was made by sonicating approximately 1 mg NSTI-Nanotech 2011, www.nsti.org, ISBN 978-1-4398-7138-6 Vol. 3, 2011 52