Fluorescent chemical sensors for bioactive amines are being developed. Because of the potential impact in neurochemistry, neurotransmitters such as dopamine and glutamate are of particular interest. The sensor system being developed is based on a substituted coumarin aldehyde which reversibly forms an iminium ion with primary amines in aqueous solution. The iminium ion forms an internal hydrogen bond which modulates the fluorescent properties of the coumarin giving a large increase in fluorescence upon interaction with the amine. This sensing method functions efficiently in high ionic strength, neutral conditions suitable for cellular work. The ‘R' group of the sensor is modified to append additional recognition elements in order to produce selective sensors.