Covalently linked silica-multiwall carbon nanotube-polyaniline network: an electroactive matrix for ultrasensitive biosensor.

A three dimensional network comprising of covalently linked multi-walled carbon nanotubes (MWNT), silica and polyaniline chains (MWNT-Silica-PANI-NW) was prepared and used as the matrix for immobilization of an enzyme (horseradish peroxidase, HRP). MWNT-Silica-PANI-NW-HRP electrode showed superior performances over the individual components and their binary combinations, in terms of enzyme stability (minimum leaching to the medium), fast electron transfer from the enzyme to the electrode (2.11s(-1)), high sensitivity (58.1microAmM(-1)) and low detection limit (1pM) for the detection of hydrogen peroxide. The interconnected silica network provides open porous frame work for effective immobilization of the redox enzyme. The PANI units and MWNTs facilitate the electron transfer process and functions as molecular cable to "wire" the primary redox site of the enzyme (HRP) to the electrode. The improved performances for MWNT-Silica-PANI-NW arise from the synergistic contributions from conducting CNT, electron mediating PANI chains and porous silica network.