Novel biomaterial based on monoamine oxidase-A and multi-walled carbon nanotubes for serotonin detection

Serotonin is a potential biomarker for diverse neuropsychiatric and neurodevelopmental disorders. In this study a novel biocomposite based on the enzyme monoamine oxidase-A (MAO-A) immobilized by covalent binding on multi-walled carbon nanotubes (MWCNT) has been developed for detection of serotonin. Immobilized MAO-A (MWCNT/MAO-A) retained 94.3% of its catalytic activity, showing good thermal and pH stability at temperatures from 35 to 40 degrees C and pH from 7-8.5. A decrease of the apparent Michaelis-Menten constant was observed compared to free MAO-A indicating an improvement of its affinity towards its substrate. Evaluation of MWCNT/ MAO-A by scanning electrochemical microscopy (SECM) demonstrated that the immobilized enzyme maintains its activity. The biocomposite was employed for successfull detection of serotonin through quantification of the enzymatically produced hydrogen peroxide (H2O2). A MWCNT/MAOA modified glassy carbon electrode (GCE) was characterized by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Electrochemical measurements were performed in simulated body fluid (SBF), obtaining a linear response of 5.67 x 10(-7) M 2.26 x 10(-6) M, with a low detection limit of 2 x 10(-7) M (35.6 ng mL(-1);S/N = 3) and a quantification limit of 6.73 x 10(-7) M (118.7 ng mL(-1);S/N = 3); values that are in range with serotonin levels found in different neurological disorders. The biocomposite have the potential to be employed in future development of biosensing devices for serotonin detection.