The macromolecular structure of purified cellulose samples is studied by second-harmonic generation (SHG) imaging microscopy. We show that the SHG contrast in both <i>Valonia</i> and <i>Acetobacter</i> cellulose strongly resembles that of collagen from animal tissues, both in terms of morphology and polarization anisotropy. Polarization analysis shows that microfibrils in each lamella are highly aligned and ordered and change directions by 90° in adjacent lamellae. The angular dependence of the SHG intensity fits well to a cos<sup>2</sup> θ distribution, which is characteristic of the electric dipole interaction. Enzymatic degradation of <i>Valonia</i> fibers by cellulase is followed in real time by SHG imaging and results in exponential decay kinetics, showing that SHG imaging microscopy is ideal for monitoring dynamics in biological systems.
© 2003 Optical Society of America
(110.0180) Imaging systems : Microscopy
(170.3880) Medical optics and biotechnology : Medical and biological imaging
(170.6900) Medical optics and biotechnology : Three-dimensional microscopy
(190.4160) Nonlinear optics : Multiharmonic generation
R. Malcom Brown, Jr., Andrew C. Millard, and Paul J. Campagnola, "Macromolecular structure of cellulose studied by second-harmonic generation imaging microscopy," Opt. Lett. 28, 2207-2209 (2003)