(672d) Dual Near Infrared Two Photon Microscopy for 3D Imaging of Biological Systems

To visualize an important (but invisible) biomolecule inside an optically-opaque sample such as a living organism, two challenges must be overcome: (i) detecting a molecule for which there exists no optical molecular recognition platform, and (ii) detecting it deep inside a sample that is not transparent. A solution to this problem hinges on visualizing biochemical dynamics in their biologically-relevant but optically-dense milieu. With a focus on deep-brain imaging, we identify scattering and absorption contributions to brain tissue optical density. From these calculations, we identify maximal brain tissue transmission to occur in two near infrared (NIR) transmission windows: 900-1300 nm and 1550-1800 nm. The former window matches the emission of several chiral species of single walled carbon nanotubes (SWNTs) and the later window overlays with their corresponding two photon excitation peaks (1). Based on these imaging optima, we present a dual NIR excitation-emission (NIR-EE) microscope that leverages NIR excitation, from a femtosecond 1640 nm erbium laser, and NIR emission, from chiral SWNTs fluorescing between 900 and 1200 nm. Fortuitously, SWNTs have been shown to be a tunable platform for sensor design, targeting different analytes including the neurotransmitter dopamine (2). We characterize SWNT dopamine nanosensor imaging capabilities demonstrating spatial 3D resolution, power response, quantum yield, and scattering profiles of dopamine nanosensors in optically-opaque media. Aforementioned figures of merit are compared to theoretical limits and Monte Carlo simulations to determine imaging quality of NIR-EE microscopy. We also show sensor-analyte response curves for dopamine using DNA-wrapped SWNTs, and a 3D reconstructed image collected by this system. NIR-EE could enable real-time imaging of biological analytes such as dopamine in their biologically-relevant setting.

1. Del Bonis O’Donnell, J.T., Page, R.H., Beyene, A.G., Tindall, E.G., McFarlane, I.R., Landry, M.P. Molecular Recognition of Dopamine with Dual Near Infrared Excitation-Emission Two-Photon Microscopy. Advanced Functional Materials (2017). DOI: 10.1002/adfm.201702112
2. Kruss, S., Landry, M.P., Ende, E.V., Lima, B.M.A., Reuel, N.F., Zhang, J., Nelson, J., Mu, B., Hilmer, A., Strano M. Neurotransmitter Detection Using Corona Phase Molecular Recognition on Fluorescent Single-Walled Carbon Nanotube Sensors. Am. Chem. Soc. (2014). DOI: 10.1021/ja410433b