Eavesdropping on Neuronal Chemical Chatter Using SWIR emissive Optical Nanosensors

Neurons communicate through chemical signaling molecules that may diffuse beyond their point of release and modulate the activity of larger neuronal networks, in a process known as volume transmission. Molecules such as dopamine belong to this class of diffusive neurotransmitters, for which real-time imaging of the signal's spatial propagation would constitute a major advance in neurochemical imaging. To this end, we present a nanoscale, short-wave infrared (SWIR) fluorescent optical reporter for dopamine and demonstrate its efficacy for imaging dopamine volume transmission. The sensor is synthesized from single wall carbon nanotubes (SWCNT) functionalized with single-strand DNA oligonucleotides and fluoresces in the tissue compatible SWIR window at 1000-1300 nm. We demonstrate that these sensors exhibit remarkable robustness that enables them to be immobilized on glass substrates for extended periods of time, on which primary dopaminergic neurons can be cultured. In this preparation, we show that our sensor-functionalized coverslips can detect synaptic dopamine efflux with remarkable spatial and temporal resolution, at length and time scales that elude conventional methods of inquiry. Our results show that SWCNT-based SWIR emissive nanosensors can relay information about neuronal signaling in a tissue-compatible optical window and constitute a versatile class of synthetic optical tools for applications in the life sciences.