Amperometric detection of dopamine in vivo with an enzyme based carbon fiber microbiosensor.

We developed a novel implantable enzyme-based carbon fiber biosensor for in vivo monitoring of dopamine. The biosensor is fabricated using tyrosinase immobilized in a biocompatible matrix consisting of a biopolymer, chitosan and ceria-based metal oxides, deposited onto the surface of a carbon fiber microelectrode with a diameter of approximately 100 microm. Tyrosinase catalyzes the conversion of dopamine to o-dopaquinone, and the reduction of o-dopaquinone, which requires a low potential difference, was detected electrochemically. The role of each component in the sensing layer was systematically investigated in relation to the analytical performance of the biosensor. In its optimal configuration, the biosensor demonstrated a detection limit of 1 nM dopamine, a linear range of 5 orders of magnitude between 10 nM and 220 microM, a sensitivity of 14.2 nA x microM(-1), and good selectivity against ascorbic acid, uric acid, serotonin, norepinephrine, epinephrine, and 3,4-dihydroxy-l-phenylalanine (L-DOPA). The system provided continuous, real time monitoring of electrically stimulated dopamine release in the brain of an anesthetized rat. Levels of dopamine up to 1.69 microM were measured. This new implantable dopamine biosensor provides an alternative to fast scan cyclic voltammetry for in vivo monitoring of dopamine.