Fluorescent Sensor for the Visualization of Amino Acid Neurotransmitters in Neurons Based on an SNAr Reaction.

Glutamate is an important excitatory neurotransmitter, while GABA is an inhibitory neurotransmitter. However, direct and accurate visualization of these important signaling agents by a chemical sensor is still very challenging. Here, a novel coumarin-based fluorescent sensor for the selective labeling and imaging of amino acids in neurons has been developed. This sensor system provides two binding sites for amino acids: an aldehyde group for the amine binding and a modified fluorobenzene for an unusual nucleophilic aromatic substitution (S_NAr) reaction of a carboxyl group. Spectroscopic studies reveal a large fluorescence enhancement upon reaction with glutamate. Compounds lacking both groups did not activate the sensor. A clear and efficient visualization of neurotransmitters in cultured hippocampus neurons was obtained by imaging studies.