title: Two-photon excited photoconversion of cyanine-based dyes.
abstract: The advent of phototransformable fluorescent proteins has led to significant advances in optical imaging, including the unambiguous tracking of cells over large spatiotemporal scales. However, these proteins typically require activating light in the UV-blue spectrum, which limits their in vivo applicability due to poor light penetration and associated phototoxicity on cells and tissue. We report that cyanine-based, organic dyes can be efficiently photoconverted by nonlinear excitation at the near infrared (NIR) window. Photoconversion likely involves singlet-oxygen mediated photochemical cleavage, yielding blue-shifted fluorescent products. Using SYTO62, a biocompatible and cell-permeable dye, we demonstrate photoconversion in a variety of cell lines, including depth-resolved labeling of cells in 3D culture. Two-photon photoconversion of cyanine-based dyes offer several advantages over existing photoconvertible proteins, including use of minimally toxic NIR light, labeling without need for genetic intervention, rapid kinetics, remote subsurface targeting, and long persistence of photoconverted signal. These findings are expected to be useful for applications involving rapid labeling of cells deep in tissue.
authors.affiliation: Harvard Medical School and Wellman Center for Photomedicine, Massachusetts General Hospital, 50 Blossom Street, Boston, Massachusetts, 02114, USA.|Harvard-MIT Health Sciences and Technology, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts, 02139, USA.
authors.forename: Sheldon J J
authors.initials: SJ
authors.lastname: Kwok
authors.affiliation: Harvard Medical School and Wellman Center for Photomedicine, Massachusetts General Hospital, 50 Blossom Street, Boston, Massachusetts, 02114, USA.|Department of Biomedical Engineering, Sungkyunkwan University and Center for Neuroscience and Imaging Research, Institute for Basic Science, 2066 Seobu-ro, Jangan-Gu, Suwon-Si, Gyeong Gi-Do, South Korea.
authors.forename: Myunghwan
authors.initials: M
authors.lastname: Choi
authors.affiliation: Harvard Medical School and Wellman Center for Photomedicine, Massachusetts General Hospital, 50 Blossom Street, Boston, Massachusetts, 02114, USA.
authors.forename: Brijesh
authors.initials: B
authors.lastname: Bhayana
authors.affiliation: Molecular Imaging Laboratory, MGH/MIT/HMS Athinoula A. Martinos Center for Biomedical Imaging, Building 149, 13th Street, Charlestown, Massachusetts, 02129, USA.|Department of Pharmacy, Zhongda Hospital, Southeast University, Nanjing 210009, China.
authors.forename: Xueli
authors.initials: X
authors.lastname: Zhang
authors.affiliation: Molecular Imaging Laboratory, MGH/MIT/HMS Athinoula A. Martinos Center for Biomedical Imaging, Building 149, 13th Street, Charlestown, Massachusetts, 02129, USA.
authors.forename: Chongzhao
authors.initials: C
authors.lastname: Ran
authors.affiliation: Harvard Medical School and Wellman Center for Photomedicine, Massachusetts General Hospital, 50 Blossom Street, Boston, Massachusetts, 02114, USA.|Harvard-MIT Health Sciences and Technology, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts, 02139, USA.
authors.forename: Seok-Hyun
authors.initials: SH
authors.lastname: Yun
mesh_terms: D000818:Animals; D002232:Carbocyanines / Q000737:chemistry* / Q000378:metabolism; D002460:Cell Line; D058948:Cell Tracking / Q000379:methods*; D004912:Erythrocytes / Q000378:metabolism* / Q000648:ultrastructure; D005456:Fluorescent Dyes / Q000737:chemistry* / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D019169:Jurkat Cells; D008027:Light; D008264:Macrophages / Q000378:metabolism* / Q000648:ultrastructure; D051379:Mice; D036641:Microscopy, Fluorescence, Multiphoton; D055668:Photochemical Processes; D019265:Spectroscopy, Near-Infrared
chemical_list: D002232:Carbocyanines; D005456:Fluorescent Dyes