Jiaqi Guo

Modification of Cellulose Nanofibrils with Luminescent Carbon Dots

Films and hydrogels consisting of cellulose nanofibrils (CNF) were modified by covalent EDC/NHS coupling of luminescent, water-dispersible carbon dots (CDs). Quartz crystal microgravimetry with dissipation monitoring (QCM-D) and surface plasmon resonance (SPR) were used to investigate the attachment of CDs on carboxymethylated CNF (CM-CNF). As the first reported use of CD in nanocellulose products, we provide proof-of-concept for the synthesis of transparent and fluorescent nanopaper and for its tunable luminescence as confirmed by confocal microscopy imaging.

On the polymorphic and morphological changes of cellulose nanocrystals (CNC-I) upon mercerization and conversion to CNC-II.

Polymorphic and morphological transformations of cellulosic materials are strongly associated to their properties and applications, especially in the case of emerging nanocelluloses. Related changes that take place upon treatment of cellulose nanocrystals (CNC) in alkaline conditions are studied here by XRD, TEM, AFM, and other techniques. The results indicate polymorphic transformation of CNC proceeds gradually in a certain range of alkali concentrations, i.e. from about 8% to 12.5% NaOH. In such transition alkali concentration, cellulose I and II allomorphs coexists. Such value and range of the transition concentration is strongly interdependent with the crystallite size of CNCs. In addition, it is distinctively lower than that for macroscopic fibers (12-15% NaOH). Transmission electron microscopy and particle sizing reveals that after mercerization CNCs tend to associate. Furthermore, TEMPO-oxidized mercerized CNC reveals the morphology of individual nanocrystal of the cellulose II type, which is composed of some interconnected granular structures. Overall, this work reveals how the polymorphism and morphology of individual CNC change in alkali conditions and sheds light onto the polymorphic transition from cellulose I to II.

Attachment of gold nanoparticles on cellulose nanofibrils via click reactions and electrostatic interactions

Hybrid materials based on cellulose nanofibrils (CNF) and gold nanoparticles (AuNPs) are synthesized and novel routes to couple AuNPs on the CNF surface are introduced. Quaternary ammonium, azido, alkyne and amino functional groups were used for the attachment of metal particles on the corresponding functionalized CNF (EPTMAC-CNF, Azido-CNF, Propargyl-CNF, Amino-CNF, respectively). The CNF-based supports were characterized by Fourier transform infrared spectroscopy and the surface charge was assessed by ζ-potential measurements. The AuNPs were attached on the functionalized CNF surface via either electrostatic interactions or click reactions. The obtained CNF/AuNPs hybrid materials were characterized using transmission electron microscopy (TEM) and inductively coupled plasma optical emission spectrometry. The obtained Bio-inorganic hybrid materials are potentially suitable for surface-enhanced Raman scattering, chemosensing and catalytic applications.

Photoluminescent Hybrids of Cellulose Nanocrystals and Carbon Quantum Dots as Cytocompatible Probes for in Vitro Bioimaging

We present an approach to construct biocompatible and photoluminescent hybrid materials comprised of carbon quantum dots (CQDs) and TEMPO-oxidized cellulose nanocrystals (TO-CNCs). First, the amino-functionalized carbon quantum dots (NH2-CQDs) were synthesized using a simple microwave method, and the TO-CNCs were prepared by hydrochloric acid (HCl) hydrolysis followed by TEMPO-mediated oxidation. The conjugation of NH2-CQDs and TO-CNCs was conducted via carbodiimide-assisted coupling chemistry. The synthesized TO-CNC@CQD hybrid nanomaterials were characterized using X-ray photoelectron spectroscopy, cryo-transmittance electron microscopy, confocal microscopy, and fluorescence spectroscopy. Finally, the interactions of TO-CNC@CQD hybrids with HeLa and RAW 264.7 macrophage cells were investigated in vitro. Cell viability tests suggest the surface conjugation with NH2-CQDs not only improved the cytocompatibility of TO-CNCs, but also enhanced their cellular association and internalization on both HeLa and RAW 264.7 cells after 4 and 24 h incubation.

Complexes of Magnetic Nanoparticles with Cellulose Nanocrystals as Regenerable, Highly Efficient, and Selective Platform for Protein Separation

We present an efficient approach to develop cellulose nanocrystal (CNC) hybrids with magnetically responsive Fe3O4 nanoparticles that were synthesized using the (Fe3+/Fe2+) coprecipitation. After 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-catalyzed oxidation of CNC, carbodiimide (EDC/NHS) was used for coupling amine-containing iron oxide nanoparticles that were achieved by dopamine ligand exchange (NH2-Fe3O4 NPs). The as-prepared hybrids (Fe3O4@CNC) were further complexed with Cu(II) ions to produce specific protein binding sites. The performance of magnetically responsive Cu-Fe3O4@CNC hybrids was assessed by selectively separating lysozyme from aqueous media. The hybrid system displayed a remarkable binding capacity with lysozyme of 860.6 ± 14.6 mg/g while near full protein recovery (∼98%) was achieved by simple elution. Moreover, the regeneration of Fe3O4@CNC hybrids and efficient reutilization for protein separation was demonstrated. Finally, lysozyme separation from matrices containing egg white was achieved, thus revealing the specificity and potential of the presented method.

Biofabrication of multifunctional nanocellulosic 3D structures: a facile and customizable route

Biomass-based nanomaterials such as bacterial cellulose (BC) are one of the most promising building blocks for the development of sustainable materials with the potential to outperform their conventional, synthetic, counterparts. The formation of BC occurs at the air–water interface, which has been exploited to engineer materials with finely controlled microtopographical features or simple three-dimensional morphologies for a wide range of applications. However, a high degree of control over the 3D morphology of BC films across several length scales (micro to macro) has not yet been achieved. Herein, we describe a simple yet customizable process to finely engineer the morphology of BC in all (x, y, z) directions, enabling new advanced functionalities, by using hydrophobic particles and superhydrophobized surfaces. This results in hollow, seamless, cellulose-based objects of given shapes and with sizes from ca. 200 μm to several centimeters. We demonstrate some of the unique properties of the process and the resulting objects via post-fabrication merging (biowelding), by in situ encapsulation of active cargo and by multi-compartmentalization for near limitless combinations, thus extending current and new applications for example in advanced carbon materials or regenerative medicine.

Interactions between fungal cellulases and films of nanofibrillar cellulose determined by a quartz crystal microbalance with dissipation monitoring (QCM-D)

Understanding the interactions between enzymes and substrates and the property changes of the substrates during the process is vital for efficiently producing fuels and chemicals from lignocellulosic biomass. In this manuscript, quartz crystal microbalance with dissipation (QCM-D) technique was employed as a tool to investigate the adsorption and hydrolysis behaviors of four fungal cellulases (Trichoderma reesei, Trichoderma viride, Aspergillus sp. and Aspergillus niger) on the substrate of nanofibrillar cellulose (NFC) film. The characterization of the cellulose films before and after enzymatic treatment was represented by atomic force microscopy. The results showed that four cellulases behaved quite differently. The cellulases from T. reesei and T. viride adsorbed onto NFC films and then the hydrolysis was carried out; and their trends represented by different overtones were similar and consistent. The cellulase from Aspergillus sp. adsorbed on the substrate to form a quite compact layer since substantial frequency changed with little dissipation variation. In term of the cellulase from A. niger, its frequency and dissipation overtones exhibited diverged behaviors. After viscoelastic modeling for cellulases except for Aspergillus sp using the multi-overtone data provided by QCM-D technique, the film properties of NFC film and adlayer were extracted and they could help to understand the interactions between cellulases and substrates.

Optical Properties of Self-Assembled Cellulose Nanocrystals Films Suspended at Planar–Symmetrical Interfaces

Hierarchically structured materials comprising rod-like, chiral, nanoparticles are commonly encountered in nature as they can form assemblies with exceptional optical and mechanical characteristics. These include cellulose nanocrystals (CNCs), which have a large potential for the fabrication of bioinspired materials mimicking those advanced properties. Fine-tuning the optomechanical properties of assemblies obtained from CNCs hinges on the transformations from suspensions of liquid crystals to long-range order in the dry state. So far, associated transitions have been studied using trivial interfaces such as planar substrates. Such transitions are explored as they evolve onto meshed supports. The meshed substrate offers a complex topology, as is encountered in nature, for the formation of CNCs films. The CNCs self-assembly occurs under confinement and support of the framework bounding the mesh openings. This leads to coexisting suspended and supported nanoparticle layers exhibiting nematic and/or chiral nematic order. Optical microscopy combined with crossed polarizers indicate that the formation of the suspended films occurs via intermediate gelation or kinetic arrest of CNCs across the meshs open areas. The formation of self-standing, ultrathin films of CNCs with tunable optical properties, such as selective reflections in the visible range (structural color), is demonstrated by using the presented simple and scalable approach.