Carbon nanotube-chitosan system for electrochemical sensing based on dehydrogenase enzymes

Multiwalled carbon nanotubes (CNT) were solubilized in aqueous solutions of a biopolymer chitosan (CHIT). The CHIT-induced solubilization of CNT facilitated their manipulations, including the modification of electrode surfaces for sensor and biosensor development. The colloidal solutions of CNT-CHIT were placed on the surface of glassy carbon (GC) electrodes to form robust CNT-CHIT films, which facilitated the electrooxidation of NADH. The GC/CNT-CHIT sensor for NADH required approximately 0.3 V less overpotential than the GC electrode. The susceptibility of CHIT to chemical modifications was explored in order to covalently immobilize glucose dehydrogenase (GDH) in the CNT-CHIT films using glutaric dialdehyde (GDI). The stability and sensitivity of the GC/CNT-CHIT-GDI-GDH biosensor allowed for the interference-free determination of glucose in the physiological matrix (urine). In pH 7.40 phosphate buffer solutions, linear least-squares calibration plots over the range 5-300 microM glucose (10 points) had slopes 80 mA M(-1) cm(-2) and a correlation coefficient 0.996. The detection limit was 3 microM glucose (S/N = 3). The CNT-CHIT system represents a simple and functional approach to the integration of dehydrogenases and electrodes, which can provide analytical access to a large group of enzymes for wide range of bioelectrochemical applications including biosensors and biofuel cells.