Near-infrared-Fourier-transform-Raman microspectroscopic imaging of flax stems

Near-infrared-Fourier-transform-Raman (NIR-FT-Raman) microscopy was employe d to image and subsequently produce in situ maps of the distribution of che mical components in flax (Linum usitatissimum,nan L.) stem tissue. Thick(si milar to 80 mu m) cross-sections of flax were cryotomed, thawed, equilibrat ed at 85% RH for >3 h and sealed under cover glasses on gold-mirrored micro scope slides. Spectra for each image pixel were collected from selected tis sue sections over the Raman shifted region 3600-300 cm(-1) at 16 cm(-1) wit h 256-512 scans and employing similar to 185 mW of focused laser power at t he sample. A computer controlled automated microscope stage was used to col lect area maps of 50-150 mu m in rectangular dimensions in 6-10 mu m steps and register them to the visible images that were captured using a CCD came ra. Data collection required 8-10 h per image. Chemical profiles were produ ced from area integrations of specific spectral regions. The chemical profi les showed the location of all of the major components of flax by anatomica l cell type. A sharp shoulder at 2850 cm(-1) in the CH stretch region provi ded evidence of waxes in the cuticular/epidermal tissue. The bands occurrin g around 1600 cm(-1), due to aromatic ring stretching vibrations, gave evid ence of lignin in core tissue and pigments in epidermal tissue. Bands occur ring between 1175-1050 cm(-1), due to COC heavy atom mixed mode vibrations, showed the greatest concentration of carbohydrate in fiber cells with less er (but significant) amounts indicated in core tissue. In addition, bands o ccurring between 870-800, 515-476 and 400-360 cm(-1) gave specific evidence for the presence of pectins, other non-cellulosic polysaccharides and cell ulose, respectively, in parenchyma tissue. Published by Elsevier Science B. V.