Amperometric biosensors for glucose based on layer-by-layer assembled functionalized carbon nanotube and poly (neutral red) multilayer film

Multiwalled carbon nanotubes (MWNTs) were treated with a mixture of concentrated sulfuric and nitric acid to introduce carboxylic acid groups to the nanotubes. Conducting polymer film was prepared by electrochemical polymerization of neutral red (NR). By using a layer-by-layer method, homogeneous and stable MWNTs and poly (neutral red) (PNR) multilayer films were alternately assembled on glassy carbon ( GC) electrodes. With the introduction of PNR, the MWNTs/PNR multilayer film system showed synergy between the MWNTs and PNR, with a significant improvement of redox activity due to the excellent electron-transfer ability of carbon nanotubes (CNTs) and PNR. The electropolymerization is advantageous, providing both prolonged long-term stability and improved catalytic activity of the resulting modified electrodes. The MWNTs/PNR multilayer film modified glassy carbon electrode allows low potential detection of hydrogen peroxide with high sensitivity and fast response time. As compared to MWNTs and PNR-modified GC electrodes, the magnitude of the amperometric response of the MWNTs/PNR composite-modified GC electrode is more than three-fold greater than that of the MWNTs modified GC electrode, and nine-fold greater than that of the PNR-modified GC electrode. With the immobilization of glucose oxidase onto the electrode surface using glutaric dialdehyde, a biosensor that responds sensitively to glucose has been constructed. In pH 6.98 phosphate buffer, nearly interference-free determination of glucose has been realized at -0.2 V vs. SCE with a linear range from 50 mu M to 10 mM and response time < 10s. The detection limit was 10 mu M glucose (S/N = 3).