Near-infrared & upconversion optogenetics

Approaches to activate deep opsins with tissue-penetrating near-infrared light instead of poorly-penetrating visible light. The best-known injects lanthanide-doped upconversion nanoparticles that absorb near-infrared and locally re-emit visible light, gating ordinary blue or green opsins from within — allowing transcranial optogenetic stimulation of deep brain structures in mice without an implanted fiber. Directly near-infrared-sensitive opsins and other nanotransducers pursue the same wireless, minimally-invasive goal.

This is an emerging, largely rodent-scale demonstration. Nanoparticle biodistribution and clearance, long-term toxicity, upconversion efficiency, and the substantial light doses needed for reliable deep activation are open concerns that keep it far from clinical use. It is conceptually distinct from the magnetic and molecular interfaces treated elsewhere, though it shares their ambition of stimulating depth without wires.