Layer-by-Layer Assembly of Multiwall Carbon Nanotube Ultrathin Films for Biosensing Applications

The unique mechanical, electrical, and optical properties of multi-walled carbon nanotubes (MWNTs) make them very attractive for the fabrication of new advanced materials. The layer-by-layer (LBL) deposition method involves the alternate adsorption of oppositely charged macromolecules such as polymers and biomacromolecules. This approach provides a simple and flexible method to produce high-strength multifunctional thin films from MWNTs and a variety of enzymes and polyions. Organophosphorus hydrolase (OPH) is an enzyme that exhibits the ability to hydrolyze a large variety of organophosphorus compounds by producing less toxic products such as p-nitrophenol and diethyl phosphate. OPH was immobilized on the surface functionalized MWNT. The LBL assembly was constructed starting with the well dispersed aqueous solutions of positively charged MWNT-Polyethyleneimine (PEI) and negatively charged MWNT-DNA. The bilayers of polyions was held together by electrostatic interaction. Furthermore, an alternate layer of positively charged MWNT-OPH and MWNT-DNA was adsorbed on five bilayers of MWNT-PEI/MWNT-DNA system. FT-IR shows the surface functionalization of MWNTs. TEM and SEM images indicating highly dispersed solutions. This system was used to detect a model organophosphate, paraoxon, with high sensitivity and stability. Absorption spectroscopy and electrochemical flow injection analysis was used as a transduction platforms.

Keywords: Organophosphorus hydrolase, paraoxon, polyethyleneimine