Fluorescent Labeling of Lignin in the Wood Pulp Fiber Wall

Fluorescent labeling of lignin in wood pulp fibers with acridine orange (AO) was investigated. The orthochromatic and metachromatic labeling conditions were explored, and the quantitative aspects of fluorescence analysis were discussed. It was found that with sufficiently low AO concentration, orthochromatic only labeling of lignin could be attained, and the fluorescence intensity of stained pulp fibers could be correlated to the lignin concentration of the pulp. The distribution of lignin across the fiber wall was clearly imaged with confocal laser scanning microscopy (CLSM) after fluorescent staining of pulp fibers.