Aug 3, 2009
Polymer nanotube bundles track NO levels
Researchers at the National University of Singapore have developed a sensor based on CuTAPc (copper tetraamino-phthalocyanine) polymer nanotubes to detect toxic gases, for example nitric oxide (NO), present in the aqueous phase. The nanostructured sensor was fabricated through template-assisted electropolymerization in anodic aluminum oxide filters. It has been shown to be extremely sensitive and intrinsically selective to specific gases at concentrations as low as one part per billion (ppb).
As reported in Nanotechnology, Gu Feng and colleagues applied a simple protocol for polymer nanotube fabrication to CuTAPc, a commonly used industrial dye, to form their surface modified device. A high surface area to volume ratio was obtained by modifying the nanotube structure on a platinum layer, which helped the team to realize a sensor with high sensitivity and a fast response towards NO.
High sensitivities and improved linear ranges were achieved through well established measurements such as differential pulse voltammetry (DPV) and differential potential amperometry (DPA). Detection limits as low as 10 nM were obtained in common voltammetric analysis with the ultra-high response current in the microamp range.
Meanwhile, electrochemical impedance spectroscopy (EIS) was introduced to determine the sensitivity of the device to variations in polymer conductivity. By comparing the data with values obtained from an equivalent circuit model simulation, it was found that the resistance of poly-CuTAPc nanotubes decreased proportionally with the NO concentration exclusively at the oxidation potential, which points towards the possibility of determining the NO concentration in the nanometre range.
In addition, a de-doping process was applied to the sensors to increase the porosity of the nanotubes, which further lowers the detection limit. This is probably because high porosity provides more active sites and/or surface area through the expulsion of embedded anions.
The scientists are currently planning to fabricate sensors that can detect more chemicals such as dopamine, hydrazine and glucose, to further extend the applications in human and environmental studies.
About the author
The work was performed in the surface chemistry lab in the Department of Chemistry, National University of Singapore (NUS), and was supported by research grant (R143-00-191-112). Gu Feng is a PhD student the department of chemistry, NUS. He is supervised by Dr Ang Siau Gek and Dr Xu Guo Qin. Dr Ang Siau Gek is an associate professor in the Department of Chemistry, NUS. Dr Xu Guo Qin is a professor and head of the Department of Chemistry, NUS.