Detection of Trace Zinc by an Electrochemical Microsensor based on Carbon Nanotube Threads Xuefei Guo, a Woo Hyoung Lee, b Noe Alvarez, c Vesselin N. Shanov, c William R. Heineman* a a Department of Chemistry, University of Cincinnati, OH, 45221-0172, USA b Oak Ridge Institute for Science and Education (ORISE) Post–Doctoral Fellow at U.S. Environmental Protection Agency, Cincinnati, Ohio 45268, USA c Smart Materials Nanotechnology Laboratory, Department of Mechanical, Industrial and Nuclear Engineering, University of Cincinnati, Cincinnati, OH, 45221-0072, USA *e-mail: William.Heineman@uc.edu Received: February 11, 2013 Accepted: April 5, 2013 Published online: May 15, 2013 Abstract Carbon nanotubes (CNTs) have attracted intense interest due to their excellent properties, such as increased elec- trode surface area, fast electron transfer rate, significant mechanical strength and good chemical stability. CNT threads, spun from shorter CNTs, inherit the advantages of CNTs, while avoiding the potential toxicity caused by in- dividual CNTs. In this work, microelectrodes based on CNT threads were used to detect trace zinc by anodic strip- ping voltammetry with an estimated detection limit of 1.4 nM without mercury or bismuth films. CNT threads showed promise for measuring trace metals in small sample volumes without stirring such as encountered in some in vivo and in vitro applications. Keywords: Anodic stripping voltammetry (ASV), Osteryoung square-wave stripping voltammetry (OSWSV), Carbon nanotube (CNT)-thread microelectrode, Trace zinc detection, Physiological pH DOI: 10.1002/elan.201300074 1 Introduction Carbon nanotubes (CNTs) have attracted intense interest due to important properties, such as increased electrode surface area [1], fast electron transfer rate [2], significant mechanical strength and good chemical stability [3, 4]. Recently, CNT modified electrodes have been used as a new material for detecting trace heavy metals by anodic stripping voltammetry (ASV) [5–7]. Most of the reports thus far use randomly ordered CNTs causing only a small portion of the CNTs to expose their ends which generally give better electrochemical performance. Studies have shown that it is the edge-plane-like nanotube ends that lead to the enhanced electrochemical activity and elec- tron-transfer rate at CNT electrodes [8]. CNT arrays that provide much better control of the arrangement of CNTs are advantageous compared with randomly ordered CNTs, including lower detection limit, increased signal- to-noise ratio, and easier manipulation [9–11]. The CNT tower electrode shows potential for in situ detection for in vivo and in vitro studies [12], because it does not need coatings of other materials such as mercury and bismuth to enhance its performance. The diameter of the CNT towers that we used for ASV was about 400 mm. Smaller electrodes using arrayed CNTs can potentially expand the applications to extracellular or even intracellular studies. CNTs) unique combination of mechanical, thermal and electrical properties makes CNT threads, or CNT fibers and yarns, even better candidates for multifunctional ma- terials [13]. CNT threads, spun from shorter CNTs, have longer length and smaller diameter [14] compared with the CNT tower or array. CNT threads have good electri- cal resistivity (0.001 W cm) and tensile strength (0.8 GPa), although their performance characteristics are not as good as those of individual CNTs. Apart from good elec- trical and mechanical properties, the CNT thread inherits the advantages of the high surface area and good electro- catalytic properties of CNTs, while avoiding the potential toxicity caused by individual CNTs in the form of small particles with a high aspect ratio. Thus, CNT threads have good potential for conducting and sensing applications. So far, CNT threads have been tested in potential appli- cations for biosensors, such as the detection of NADH oxidation [15] and glucose [16]. As far as we know, there is no report of CNT threads used for trace metal detec- tion. Zinc ion is used as the model system in this research to explore possible applications of CNT threads since zinc, the second most abundant heavy metal after iron, is an essential component of many protein scaffolds (e.g., car- bonic anhydrase and zinc finger proteins) and is critical to many cellular functions [17]. Highly sensitive tech- niques and instruments for detecting zinc have been de- veloped. Fahrni and co-workers presented an excellent Electroanalysis 2013, 25, No. 7, 1599 – 1604 # 2013 Wiley-VCH Verlag GmbH &Co. KGaA, Weinheim 1599 Full Paper