RT Journal Article SR Electronic T1 Molecular Recognition of Dopamine with Dual Near Infrared Excitation-Emission Two-Photon Microscopy JF bioRxiv FD Cold Spring Harbor Laboratory SP 145912 DO 10.1101/145912 A1 Jackson Travis Del Bonis-O’Donnell A1 Ralph H. Page A1 Abraham G. Beyene A1 Eric G. Tindall A1 Ian R. McFarlane A1 Markita P. Landry YR 2017 UL http://biorxiv.org/content/early/2017/06/04/145912.abstract AB A key limitation for achieving deep imaging in biological structures lies in photon attenuation of fluorescence. In particular, neurotransmitter imaging is challenging in the biologically-relevant context of the intact brain, for which photons must traverse the cranium, skin, and bone. Thus, fluorescence imaging is limited to the surface cortical layers of the brain, only achievable with a craniotomy. Herein, we describe optimal excitation and emission wavelengths for through-cranium imaging, and demonstrate that near-infrared emissive nanosensors can be photoexcited using a two-photon 1550 nm excitation source. Dopamine-sensitive nanosensors can undergo 2-photon excitation, and provide chirality-dependent responses selective for dopamine with fluorescent turn-on responses varying between 20% and 350%. We further calculate the 2-photon absorption cross-section and quantum yield of dopamine nanosensors, and confirm a 2-photon power law relationship for the nanosensor excitation process. Finally, we show improved image quality of nanosensors imbedded 2 mm deep into a brain-mimetic tissue phantom, whereby 1-photon excitation yields 42% scattering, in contrast to 4% scattering when the same object is imaged under 2-photon excitation. Our approach overcomes traditional limitations in deep-tissue fluorescence microscopy, and can enable neurotransmitter imaging in the biologically-relevant milieu of the intact and living brain.