Potentiometric urea biosensor based on multi-walled carbon nanotubes (MWCNTs)/silica composite material

A novel potentiometric urea biosensor has been fabricated with urease (Urs) immobilized multi-walled carbon nanotubes (MWCNTs) embedded in silica matrix deposited on the surface of indium tin oxide (ITO) coated glass plate. The enzyme Urs was covalently linked with the exposed free –COOH groups of functionalized MWCNTs (F-MWCNTs), which are subsequently incorporated within the silica matrix by sol–gel method. The Urs/MWCNTs/SiO2/ITO composite modified electrode was characterized by Fourier transform infrared (FTIR) spectroscopy, thermal gravimetric analysis (TGA) and UV–visible spectroscopy. The morphologies and electrochemical performance of the modified Urs/MWCNTs/SiO2/ITO electrode have been investigated by scanning electron microscopy (SEM) and potentiometric method, respectively. The synergistic effect of silica matrix, F-MWCNTs and biocompatibility of Urs/MWCNTs/SiO2 made the biosensor to have the excellent electro catalytic activity and high stability. The resulting biosensor exhibits a good response performance to urea detection with a wide linear range from 2.18 × 10− 5 to 1.07 × 10− 3 M urea. The biosensor shows a short response time of 10–25 s and a high sensitivity of 23 mV/decade/cm2.