We developed a novel biosensor, which used the uniform graphene oxide (GO) to afford gold nanoparticles (GNPs). The advantages of this biosensor are the better sensitivities not only of GO but also the GNPs fabricated on it for neurotransmitters, especially the lower cost in biosensor modification. The modified composite was characterized with scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), energy dispersive spectroscopy (EDS) and electrochemical methods. The determination conditions were optimized and the peak currents of DA and 5-HT were linear, with the concentrations in the range of 9.0 x 10(-7) to 7.0 x 10(-5) M for DA, and 6.0 x 10(-7) to 4.0 x 10(-5) M for 5-HT. The detection limits were 7.0 x 10(-9) M for 5-HT and 5.6 x 10(-8) M for DA. A microcapacity electrolytic cell was designed using the modified biosensor to connect to the microdialysis device and it was successfully applied to determine the concentrations of DA and 5-HT in the samples, with a spiked recovery of 82.0-118%.