Overoxidized polypyrrole film directed DNA immobilization for construction of electrochemical micro-biosensors and simultaneous determination of serotonin and dopamine

A promising electrochemical microsensor was fabricated by electrochemical immobilization of calf-thymus DNA on a carbon fiber electrode (CFE) through an overoxidized polypyrrole (PPyox) template for simultaneous determination of serotonin (5-HT) and dopamine (DA). Such a DNA–PPyox biocomposite modification layer of nano-thickness exhibited superior selectivity and sensitivity towards these neuronal amines comparing with a simple PPyox or DNA coating. This microsensor gave three separated differential pulse voltammetric (DPV) peaks at 0.38, 0.20 and −0.02 V for 5-HT, DA and 25,000-fold excess of ascorbic acid (AA). The linear response was obtained in the range of 1.0 × 10 −8 to 1.0 × 10 −6 M with a detection limit of 7.0 × 10 −9 M for 5-HT, and in the range of 3.0 × 10 −7 to 1.0 × 10 −5 M with a detection limit ( s/ n = 3.0) of 5.0 × 10 −8 M for DA. A stronger interaction of 5-HT with the modification layer was observed, which led to a higher detection sensitivity for 5-HT than for DA. The utility of this modified electrode was demonstrated by the determination of 5-HT and DA in human blood serum.