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

While other tools are emerging to optically report dopamine fluctuations via cell-surface engineered proteins, 33, 34 nIRCats are likely to fulfill a niche amongst currently available methods for detecting dopamine neurotransmission due to their unique near-infrared fluorescence, the fact that they do not rely on genetic delivery and expression, and the functionality of nIRCats in the presence of pharmacological dopamine receptor ligands. This is in contrast to receptor-based fluorescent sensors which currently cannot report on endogenous dopamine dynamics in the presence of ligands to the engineered receptor. 33, 34 Furthermore, the synthetic nature of nIRCats affords complete elimination of potential GPCR-mediated residual signaling that may be present in protein-based optical probes. nIRCats also offer spatial advantages over FSCV, and our initial experiments suggest that the temporal resolution of the nIRCat signal can be comparable to that of FSCV. nIRCat decay profiles exhibit a wider range than that observed from FSCV data and included a significant number of ROIs that showed seconds-long time constants. It is debatable if these results capture the unique spatial properties of specific striatal ROIs or are related to tool differences alone. nIRCats, unlike FSCV probes, should sample catecholamine concentration at a single point in space, such that each distributed nIRCat construct can act as a probe within the ECS and therefore yield a "higher resolution" picture of catecholamine dynamics. Future experiments will investigate how the heterogeneity of nIRCat signals (amplitude and kinetics) relates to structural and functional properties at dopamine terminals and within the ECS. We predict that new optical tools for measuring dopamine dynamics with high spatial resolution will be enable new insights into the regulation of dopamine release and reuptake at the level of individual synapses. [35] [36] [37] In the future, we see potential for expansion of a larger family of SWNT based nearinfrared nanosensors (nIRNS) similar to nIRCats for multiple neurochemical imaging applications. Several lines of evidence illustrate their future potential. First, nIRNS are easily functionalized with a wide range of synthetic molecular recognition moieties, affording fine control of their surface functional elements and their interactions with the local chemical environment. [38] [39] [40] SWNT fluorescence can be finely tuned to monochromatic emission in the near-infrared II (1000-1700 nm) window by controlling the SWNT chirality. 41 This chirality-dependent fluorescence in the near-infrared II window provides further avenues for designing color-specific responses to multiple molecular analytes simultaneously, thereby affording synthesis of ratiometric and multiplexed analyte imaging platforms, as we have shown previously. 42 Second, SWNT-based nanosensors rely on near-infrared fluorescence, which greatly reduces the impact of tissue scattering in the emission window and therefore may enable through-cranium imaging. 21 nIRNS are compatible with multi-photon imaging with 1600 nm excitation 43 and as such could permit nanoscale imaging of intact neuronal structures pending parallel developments in allinfrared microscopy, as has been shown with visible wavelength-emitting fluorophores. 44 Third, nIRNS have robust photostability allowing for use in long-term imaging experiments. 45 Fourth, because nIRNS are not genetically-encoded, they could enable use