Imaging Striatal Dopamine Release Using a Non-Genetically Encoded Near-Infrared Fluorescent Catecholamine Nanosensor

Abraham G. Beyene; Kristen Delevich; Jackson Travis Del Bonis-O’Donnell; David J. Piekarski; Wan Chen Lin; A. Wren Thomas; Sarah J. Yang; Polina Kosillo; Darwin Yang; Linda Wilbrecht; Markita P. Landry

We report near-infrared fluorescent catecholamine nanosensors (nIRCats) that enable imaging of extrasynaptic catecholamines and their release and re-uptake dynamics in the ECS of brain tissue. Using a previously established nanosensor generation platform 22, 23 , synthetic bio-mimetic polymers were pinned onto the surface of intrinsically near-infrared fluorescent single-wall carbon nanotubes (SWNT). The resulting non-covalent nanometerscale conjugate produced the catecholamine-selective nIRCat. In in vitro solution phase experiments (Methods), nIRCats exhibited a maximal change in fluorescence (ΔF/F) of up to 24 (Figure 1b, 1c) with a dynamic range of 4 orders of magnitude, reporting detectable fluorescence changes from 10 nM to 100 µM dopamine concentration ( Figure S1 ). nIRCats were also sensitive to norepinephrine with a maximal response of ∆F/F=35 and a similar dynamic range ( Figure S1 ). We found that nIRCats are insensitive to GABA, glutamate, and acetylcholine ( Figure 1c ) and can report fluctuations in dopamine concentration in the presence of ascorbic acid, which is present in cerebrospinal fluid ( Figure S1 ). Singlemolecule imaging revealed that the nIRCat signal in response to repeated perfusions of 10 µM dopamine was reversible upon exposure, an important feature for measuring neuromodulator kinetics ( Figure S2 ). In previous work, we performed stochastic simulations that suggest nIRCats have sufficient sensitivity to detect physiologically relevant fluctuations in dopamine concentration in brain tissue arising from the activity of a single dopaminergic terminal, which can briefly exceed concentrations of 1 µM from the release site in a distance-dependent manner. 24