This communication reports a promising platform for rapid, simple, direct, and ultrasensitive determination of serotonin. The method is related to integration of vertically aligned singlewalled carbon nanotubes (SWCNTs) in electrochemical microfluidic devices. The required microfabrication protocol is simple and fast. In addition, the nanomaterial influenced remarkably the obtained limit-of-detection (LOD) values. Our system achieved a LOD of 0.2 nmol L 21 for serotonin, to the best of our knowledge one of the lowest values reported in the literature.Glass/elastomer hybrid microfluidic platforms with integrated electrochemical detectors are powerful analytical tools. Their main advantages include: (i) low cost; (ii) chemical inertia; (iii) optical transparency; (iv) thermal, mechanical, and chemical stability; (v) automation capacity, and; (vi) easy microfabrication. In addition, they offer high values of reproducibility and sensitivity.