title: Polarization-sensitive sum-frequency generation microscopy of collagen fibers.
abstract: Point-scanning sum-frequency generation (SFG) microscopy enables the generation of images of collagen I fibers in tissues by tuning into specific vibrational resonances of the polypeptide. It is shown that when collagen-rich tissues are visualized near the 2954 cm(-1) stretching vibration of methylene groups, the SFG image contrast is higher compared to the contrast seen in nonresonant second-harmonic generation (SHG) imaging. Polarization and spectrally resolved analysis of the SFG signal as a function of fiber orientation in the CH-stretching range of the vibrational spectrum enabled a comparative characterization of the achiral tensor elements of collagen's second-order susceptibility. This analysis reveals that selected on-resonance tensor elements are enhanced over other elements, giving rise to a much stronger anisotropy ρ of the signal for SFG (ρ ≈ 15) compared to SHG (ρ ≈ 3). The improved anisotropy of the vibrationally resonant signal contributes to the higher contrast seen in the SFG tissue images.
authors.affiliation: Department of Chemistry, University of California at Irvine , Irvine, California 92697-2025, United States.
authors.forename: Yang
authors.initials: Y
authors.lastname: Han
authors.forename: Julie
authors.initials: J
authors.lastname: Hsu
authors.forename: Nien-Hui
authors.initials: NH
authors.lastname: Ge
authors.forename: Eric O
authors.initials: EO
authors.lastname: Potma
mesh_terms: D000818:Animals; D016880:Anisotropy; D030161:Avian Proteins / Q000737:chemistry; D003094:Collagen / Q000737:chemistry*; D003315:Cornea / Q000737:chemistry; D046428:Hawks; D008853:Microscopy / Q000379:methods*; D051381:Rats; D013057:Spectrum Analysis; D013623:Tail / Q000737:chemistry; D013710:Tendons / Q000737:chemistry; D014732:Vibration
chemical_list: D030161:Avian Proteins; D003094:Collagen