Electrochemical detection of glucose at physiological pH using gold nanoparticles deposited on carbon nanotubes

There is currently considerable interest in the development of non-enzymatic glucose sensors and gold is one of the noble metals that enables the oxidation of glucose. Gold nanoparticles with a mean diameter of 7.5 nm were deposited onto the walls of functionalised carbon nanotubes to give a gold loading of 2.0% by weight. This composite was dispersed and cast onto glassy carbon and carbon screen printed electrodes. These electrodes were then used to detect glucose in a neutral phosphate buffer solution, corresponding to physiological pH. Using constant potential amperometry, a linear calibration curve was obtained with a sensitivity of 2.77 +/- 0.14 mu A/mM, a limit of detection, LOD, of 4.1 mu M and a linear region extending to 25 mM. This sensor showed very good selectivity in the presence of ascorbic acid, galactose and fructose, but interference was observed in the presence of uric acid. This interference was eliminated by applying a Nafion((R)) film to the composite electrodes. Due to a lower diffusion of glucose across the Nafion ((R)) barrier, the sensitivity of the Nafion((R) )coated composite was reduced to 0.55 +/- 0.03 mu A/mM and the LOD was increased to 10.0 mu M. However, a linear response between 0.1 mM and 25 mM was obtained, which covers the normal and elevated levels of glucose in blood. These sensors showed very good stability when stored in air and it was also possible to re-use the sensors.