Aligned multiple-wall carbon nanotubes as biosensors for phenols

Vertically oriented multiple-walled carbon nanotubes (MWCNTs) aligned on a silicon substrate were covalently bonded with horseradish peroxidase (HRP) and used as biosensors or electrodes. The modified platform was investigated with Scanning Electron Microscopy (SEM), UV-VIS spectrophotometer and Cyclic Voltammetry (CV). The enzyme catalyzed reaction and the subsequent reduction of the enzymatic products by the platform were carefully investigated. The typical SEM micrographs of MWCNT-chip before and after HRP immobilization are obviously different. The colorimetric assay was done by measuring the absorbance of the dye formed from the reaction product of the substrates (phenol) and 4-aminoantipyrine. From the linear response, phenol can be quantitated in the range from 0.5 mM to 8.0 mM. The electrodes exhibited excellent electrochemical activity in aqueous solution, and the linearity range for phenol concentration lied up to 0.6 mM. The resulting modified aligned MWCNTs still exhibited enzymatic activities after storage of 13 days.