title: Label-free live-cell imaging of nucleic acids using stimulated Raman scattering microscopy.
abstract: Imaging of nucleic acids is important for studying cellular processes such as cell division and apoptosis. A noninvasive label-free technique is attractive. Raman spectroscopy provides rich chemical information based on specific vibrational peaks. However, the signal from spontaneous Raman scattering is weak and long integration times are required, which drastically limits the imaging speed when used for microscopy. Coherent Raman scattering techniques, comprising coherent anti-Stokes Raman scattering (CARS) and stimulated Raman scattering (SRS) microscopy, overcome this problem by enhancing the signal level by up to five orders of magnitude. CARS microscopy suffers from a nonresonant background signal, which distorts Raman spectra and limits sensitivity. This makes CARS imaging of weak transitions in spectrally congested regions challenging. This is especially the case in the fingerprint region, where nucleic acids show characteristic peaks. The recently developed SRS microscopy is free from these limitations; excitation spectra are identical to those of spontaneous Raman and sensitivity is close to shot-noise limited. Herein we demonstrate the use of SRS imaging in the fingerprint region to map the distribution of nucleic acids in addition to proteins and lipids in single salivary gland cells of Drosophila larvae, and in single mammalian cells. This allows the imaging of DNA condensation associated with cell division and opens up possibilities of imaging such processes in vivo.
authors.affiliation: Department of Chemistry and Chemical Biology, Harvard University, 12 Oxford Street, Cambridge, MA 02138, USA.
authors.forename: Xu
authors.initials: X
authors.lastname: Zhang
authors.forename: Maarten B J
authors.initials: MB
authors.lastname: Roeffaers
authors.forename: Srinjan
authors.initials: S
authors.lastname: Basu
authors.forename: Joseph R
authors.initials: JR
authors.lastname: Daniele
authors.forename: Dan
authors.initials: D
authors.lastname: Fu
authors.forename: Christian W
authors.initials: CW
authors.lastname: Freudiger
authors.forename: Gary R
authors.initials: GR
authors.lastname: Holtom
authors.forename: X Sunney
authors.initials: XS
authors.lastname: Xie
mesh_terms: D000818:Animals; D045744:Cell Line, Tumor; D004247:DNA / Q000737:chemistry*; D004331:Drosophila melanogaster; D057809:HEK293 Cells; D006801:Humans; D012469:Salivary Glands / Q000166:cytology; D013059:Spectrum Analysis, Raman
chemical_list: D004247:DNA