SignificanceEfforts starting more than 20 years ago led to increasingly well performing genetically encoded voltage indicators (GEVIs) for optical imaging at wavelengths <600 nm. Although optical imaging in the >600 nm wavelength range has many advantages over shorter wavelength approaches for mesoscopic in vivo monitoring of neuronal activity in the mammalian brain, the availability and evaluation of well performing near-infrared GEVIs are still limited.AimHere, we characterized two recent near-infrared GEVIs, Archon1 and nirButterfly, to support interested tool users in selecting a suitable near-infrared GEVI for their specific research question requirements.ApproachWe characterized side-by-side the brightness, sensitivity, and kinetics of both near-infrared GEVIs in a setting focused on population imaging.ResultsWe found that nirButterfly shows seven-fold higher brightness than Archon1 under the same conditions and faster kinetics than Archon1 for population imaging without cellular resolution. But Archon1 showed larger signals than nirButterfly.ConclusionsNeither GEVI characterized here surpasses in all three key parameters (brightness, kinetics, and sensitivity), so there is no unequivocal preference for one of the two. Our side-by-side characterization presented here provides new information for future in vitro and ex vivo experimental designs.
Our study exploits Rhodopseudomonas palustris BphP1 bacterial phytochrome to generate a near-infrared (NIR) loxP-BphP1 photoswitchable transgenic mouse model that enables deep-tissue optogenetics and photoacoustic tomography (PAT). BphP1 incorporates biliverdin and reversibly switches between the ground state and activated state, with distinct optical absorption spectra in the NIR window. We validated the optogenetic performance of the BphP1-encoded mouse model to trigger gene transcription, and demonstrated its superior capability of deep-tissue optogenetics. Then, taking advantage of BphP1's photoswitching properties, we can suppress the non-switching signals from background blood and improve the molecular detection sensitivity of PAT by three orders of magnitude.
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