Detection of biogenic monoamines in nanomolar concentrations is of great importance for probing the brain chemistry and for their analytics in biological fluids. The sensitivity enhancement of amperometric detection of neurotransmitters (NTs) and their metabolites after their electrophoretic separation on a microchip is presented and is based on coupled enzymatic reactions. The current response of the analyte is amplified by cyclic oxidation on a gold electrode mediated by reduced nicotinamide dinucleotide coenzyme and glucose oxidase enzyme present in the electrophoresis buffer. Using this approach, detection limits of about 10 nm for NTs and their metabolites can be reached.