A new combined imaging and chemical detection sensor for the measurement of localized l-glutamate release at the insect neuromuscular junction (NMJ) is presented. The sensor is comprised of an l-glutamate-sensitive fluorescent gel, spin-coated onto the tip of an optical imaging fiber. The gel is composed of l-glutamate oxidase (GLOD); a pH-sensitive fluorescent dye, SNAFL; and poly(acrylamide-co-N-acryloxysuccinimide) (PAN). NH 3 is liberated from the interaction of l-glutamate with GLOD, which reversibly reduces the emitted fluorescence signal from SNAFL. This sensor has a spatial resolution of 3-4 μm, and an l-glutamate detection limit of between 10 and 100 μM. l-glutamate release and re-uptake from the foregut plexus of Manduca sexta was detected by the sensor in the presence of the l-glutamate re-uptake blocker dihydrokainate, and the post-synaptic l-glutamate receptor antagonist CNQX.