Fluorescent Labeling and Characterization of Cellulose Nanocrystals with Varying Charge Contents

Abstract

Cotton-source cellulose nanocrystals (CNCs) with a range of surface charge densities were fluorescently labeled with 5-(4, 6-dichlorotriazinyl) aminofluorescein (DTAF) in a facile, one-pot reaction under alkaline conditions. Three CNC samples were labeled: (I) anionic CNCs prepared by sulfuric acid hydrolysis with a sulfur content of 0.47 wt %, (II) a partially desulfated, sulfuric acid-hydrolyzed CNC sample, which was less anionic with an intermediate sulfur content of 0.21 wt %, and (III) uncharged CNCs prepared by HCl hydrolysis. The DTAF-labeled CNCs were characterized by dynamic light scattering, atomic force microscopy, fluorescence spectroscopy and microscopy, and polarized light microscopy. Fluorescent CNCs exhibited similar colloidal stability to the starting CNCs, with the exception of the HCl-hydrolyzed sample, which became less agglomerated after the labeling reaction. The degree of labeling depended on the sulfur content of the CNCs, indicating that the presence of sulfate half-ester groups on the CNC surfaces hindered labeling. The labeling reaction produced CNCs that had detectable fluorescence, without compromising the overall surface chemistry or behavior of the materials, an aspect relevant to studies that require a fluorescent cellulose substrate with intact native properties. The DTAF-labeled CNCs were proposed as optical markers for the dispersion quality of CNC-loaded polymer composites. Electrospun polyvinyl alcohol fibers loaded with DTAF-labeled CNCs appeared uniformly fluorescent by fluorescence microscopy, suggesting that the nanoparticles were well dispersed within the polymer matrix.

Coumarin and carbazole fluorescently modified cellulose nanocrystals using a one‐step esterification procedure

“…This corresponds to a crystallinity drop of The amount of grafted fluorophores is very significant and consists of a large increase when compared with the work of Nielsen et al [20] which reported grafted amounts of [24] or 0.02-0.2 μmol/g 5-(4, 6-dichlorotriazinyl) aminofluorescein (DTAF) achieved by Abitbol et al [44] The absorption spectra of the Cz-a-CNC1, Cz-a-CNC2 and Cz-a-CNC3 ( proportional with the absorption peaks while with increasing concentration, e.g. at 0.08 mg/mL, all the emission spectra display almost the same intensity (Figure 8).…”

Increased thermal stability of nanocellulose composites by functionalization of the sulfate groups on cellulose nanocrystals with azetidinium ions

“…Table shows the different sulfur contents (%S) and the zeta potential after the different treatments of CNCs. The sulfur content was measured using elemental analysis, and the value for the original CNC sample (CNC‐2) was in the same range as the CNC sulfur content reported by other research groups . From Table , it can be seen that the two samples that were desulfated had lower sulfur content and a higher zeta potential compared with the original CNCs.…”

Polydispersity and assembling phenomena of native and reactive dye-labelled nanocellulose

“…Their visualisations by scanning electron microscopy (SEM) or atomic force microscopy (AFM) require time and effort for detailed observation due to small observation fields (AFM in particular) making these techniques prohibitive for detailed analysis (Iwamoto et al 2013). As an alternative, fluorescent labelling (using FITC (Dong and Roman 2007), isothiocyanate, succinimidyl ester, pyrene, dichlorotriazine (Abitbol et al 2013;Huang et al 2013), etc. allows extensive microscopy studies (from trivial, distribution patterns' observations up to distribution and cellular uptake follow-up (Generalova et al 2009).…”