Inhomogeneity of Cellulose Microfibril Assembly in Plant Cell Walls Revealed with Sum Frequency Generation Microscopy
S. Huang, M. Makarem, S. N. Kiemle, H. Hamedi, M. Sau, D. J. Cosgrove and S. H. Kim
J. Phys. Chem. B 122, 5006−5019 (2018)
Sum frequency generation (SFG) vibrational spectroscopy can
selectively detect and analyze noncentrosymmetric components interspersed in
amorphous matrices; this principle has been used for studies of nanoscale structure
and mesoscale assembly of cellulose in plant cell walls. However, the spectral
information averaged over a large area or volume cannot provide regiospecific or
tissue-specific information of different cells in plants. This study demonstrates
spatially resolved SFG analysis and imaging by combining a broad-band SFG
spectroscopy system with an optical microscope. The system was designed to
irradiate both narrow-band 800 nm and broad-band tunable IR beams through a
single reflective objective lens, but from opposite sides of the surface normal
direction of the sample. The developed technique was used to reveal
inhomogeneous distributions of cellulose microfibrils within single cell walls, such
as cotton fibers and onion epidermis as well as among different tissues in
Arabidopsis inflorescence stems and bamboo culms. SFG microscopy can be used
for vibrational spectroscopic imaging of other biological systems in complement to conventional Fourier transform infrared
spectroscopy and confocal Raman microscopy