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