Too bad Jules Verne isn’t around to read PNAS vol. 114 pp. 1789 – 1794 ’17 where 20,000 fluorescent nanoSensors were placed under a single PC12 cell. PC12 cells are derived from a pheochromocytoma, a tumor which secretes catecholamines like dopamine and norepinephrine. So they’re almost neurons, and they contain vesicles containing dopamine, just like neurons, but they don’t form synapses.
The pictures they show of the cells shows the cell bodies sitting on a slide to be about 100 microns in diameter, with multiple protrusions so how are you going to get 20,000 sensors underneath them. Assuming them to be circular that’s about 3 per square micron. A micron is 10,000 Angstroms. The authors used Single Walled Carbon NanoTubes (SWCNTs) — e.g. rolled up graphene. They have a diameter of from 5 – 20 Angstroms, so there’s plenty of room for many in a square micron.
Here’s what they did. “Previously we found that the corona phase around SWCNTs can be engineered to recognize certain small analytes––a phenomenon we termed Corona Phase Molecular Recognition (CoPhMoRe) (7, 25, 26). Specifically, DNA-wrapped SWCNTs were found to increase their near InfraRed fluorescence in the presence of catecholamines . Here, we synthesized and characterized different DNA/SWCNT com- plexes and identified the best candidates for dopamine detection.
What they found is less remarkable than having the guts to try something like this. They could stimulate the cells to release dopamine using potassium (maddeningly I couldn’t find the concentration anywhere). Then with the density of sensors they could find out where it was released (the edges of the cell) with a time resolution of .1 second. It wasn’t generally released, but in hotspots — what you’d expectd if it were being released due to vesicles containing dopamine fusing with the cell membrane.
Remarkable — hard to see how they’re going to get this sort an array into a living organism, but their use in the study of brain slices can’t be far away.