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Surface enhanced Raman scattering spectroscopy (SERS) technology has received increasing attention in the bioimaging field. Herein, based on the support of cellulose nanocrystal (CNC) with thiol groups, one-dimensional (1D) "hot spot" structure was constructed by the self-assembly of gold nanoparticles (AuNPs) via Au-S bonding. Silica shell was subsequently coated on the CNC loaded with AuNPs to fabricate core-shell SERS nanoprobe, which was further successfully applied for the SERS imaging of Hela cells. Owing to the presence of silica shell, the nanoprobe exhibited excellent water-dispersible stability in phosphate buffer salt solution (PBS). Moreover, the silica shell effectively protected both the "hot spot" structure and the adsorbed Raman reporter of 4-mercaptobenzoic acid from external interference, thereby improving the signal stability of SERS nanoprobe. In addition, the plasma coupling of electromagnetic field between AuNPs and silica significantly enhanced the Raman signal of "hot spots". The SERS nanoprobe possessed good biocompatibility even at relatively high concentrations, and successfully achieved bioimaging of Hela cell using the Raman signal at 1580 cm−1 channel. [Display omitted] • 1D "hot spot" was constructed based on cellulose nanocrystal via Au-S bonding. • Silica shell improved the dispersion stability and enhanced the Raman signal. • The 1D SERS nanoprobe achieved successful bioimaging of Hela cell. [ABSTRACT FROM AUTHOR]

Superamphiphobic aerogels of cellulose nanofibrils (CNF) were successfully fabricated based on their porous rough structure via the chemical vapor deposition of fluorosilane reagent. FE-SEM images show the protruding nano-filaments, micron fibrils and sheet-like layers in the nanocellulose aerogel constitute the micro–nano hierarchical structure, which is critically important for the superamphiphobic performance. The lyophobicity increases with an increase in the nanocellulose concentration within the range of 0.5–2.0 wt%. For the fluorinated aerogel with CNF concentration of 2.0 wt%, the contact angles of water, castor oil, and hexdecane reach 163°, 154° and 143°, respectively. In addition, the loading of SiO2 nanoparticles in the CNF aerogels was conducted to increase the proportion of the nanoscale protuberance on the aerogel surface. The combination of nanocellulose and the loaded SiO2 nanoparticles optimizes the micro–nano hierarchical structure, which further improves the superamphiphobic performance with the contact angle of hexdecane reaching 150°. The superamphiphobic CNF-based composite aerogels with excellent liquid repellency for both water and oil can be used as potential self-cleaning substrates in the fields of gas sensors, catalysis, supercapacitor, and etc. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Fluorescent cellulose nanocrystals (CNC) labeled with 1, 8-naphthalimide dye. • High dye content via covalent carboxyl attachment. • High fluorescence responsiveness to solvent polarity and ion strength. • Aggregation-enhanced emission based on sensitive colloidal stability of CNC. Abstract Fluorescent and stimuli-responsive cellulose nanocrystals (CNC) were prepared via covalent conjugation of a 1, 8-naphthalimide dye onto TEMPO-oxided CNC. The structural and morphological integrity of CNC were essentially not affected by the functionalizaiton, in spite of their relatively high dye content of 0.1 ± 0.01 mmol g−1. The dye-labeled CNC show much higher fluorescence sensitivity to solvent polarity and ion concentration compared to pure dye. The fluorescence emission of dye-labeled CNC is greatly enhanced when reducing solvent permittivity or increasing ionic strength. The magnified fluorescence responsiveness is attributed to the effect of aggregation-enhanced emission (AEE) based on the sensitive colloidal stability of CNC to medium conditions. Under high ionic strength and low solvent permittivity, the compressed double layers of CNC lead to space restriction and steric hindrance of dye groups, which limit the process of nonradiative transition. The aggregation of CNC triggered by the change of ion concentration was supported by dynamic light scattering (DLS) particle sizes and Zeta potential values. Owing to the special AEE effect, the fluorescent CNC are promising sensing nanomaterials for wide applications. [ABSTRACT FROM AUTHOR]

Elongated nanoparticles show distinct advantages over spherical nanoparticles in bioimaging because of surface area-to-volume, rate of clearance from the body and elimination mechanism. In this work, we investigated the fluorescence emission properties of the hybrid system by decorating silver sulfide quantum dots (Ag 2 S QDs) in situ on the surface of cellulose nanocrystal (CNC) with unique rod shape, modifiability and biocompatibility. This water-dispersible fluorescent probe has both absorption and fluorescence in near-infrared (NIR) region. By varying the amount of surface ligands, uniformly dispersed Ag 2 S QDs with different crystalline states but similar sizes were prepared due to the anchoring effect of CNC. The fluorescence quantum yield of fluorescent probes can be improved up to 109-fold (from 0.04 % to 4.36 %). In addition, the CNC-restricted interparticle spacing of Ag 2 S QDs (< 10 nm), in combination with the overlap of wide fluorescence emission and ultraviolet absorption, significantly enhanced the 1070 nm emission in the NIR-II region via fluorescence resonance energy transfer (FRET). Further conjugation of these CNC probes with folic acid-polyethylene glycol-amino (FA-PEG-NH 2) enables in vitro bioimaging of Hela cells, which are potentially applicable for in vivo cancer detection system. The synthetic strategy provides a new way for one-pot preparation of fluorescent probes with both high NIR-I absorption and NIR-II fluorescence. • Ag 2 S QDs were controllably loaded on CNC via in situ grown. • Both the absorption and fluorescence of the nanocomposite were located in the NIR region. • FRET between Ag 2 S QDs was realized to enhance the NIR-II fluorescence intensity. • NIR-II fluorescence imaging of the CNC-based fluorescent probe in Hela cells was completed for the first time. [ABSTRACT FROM AUTHOR]

• Nanocellulose is an excellent supporting substrate to load nano-structured materials. • Inorganic nanomaterials can be linked with nancellulose physically or chemically. • The synergistic effect of nancellulose and inorganic nanomaterials leads to unique properties. • The nanocomposites show wide applications in conventional and high-grade fields. Nanocellulose obtained from natural renewable resources has attracted enormous interests owing to its unique morphological characteristics, excellent mechanical strength, biocompatibility and biodegradability for a variety of applications in many fields. The template structure, high specific surface area, and active surface groups make it feasible to conduct surface modification and accommodate various nano-structured materials via physical or chemical deposition. The review presented herein focuses on the methodologies of loading different nano-structured materials on nanocellulose, including metals, nanocarbons, oxides, mineral salt, quantum dots and nonmetallic elements; and further describes the applications of nanocellulose composites in the fields of catalysis, optical electronic devices, biomedicine, sensors, composite reinforcement, photoswitching, flame retardancy, and oil/water separation. [ABSTRACT FROM AUTHOR]

Fluorescent nanoprobe with good water dispersibility was synthesized by the coupling of fluorescent 1,8-naphthalimide dye (NANI) as well as biocompatible poly (ethylene glycol) (PEG) to cellulose nanocrystals (CNC). FTIR, TGA and XPS analysis confirmed the successful covalent conjugation of NANI and PEG. The rod-like morphology of CNC was generally retained after two-step successive grafting of NANI and PEG. The contact angle and transmittance measurements showed that the grafted PEG brushes improve the hydrophilicity of fluorescent CNC probes and their dispersibility in high-concentration NaCl solutions. The fluorescent CNC probe had good biocompatibility and was successfully used for the bioimaging of Hela cells in physiological environment at high salt concentration. Laser confocal microscopy showed that the fluorescent CNC probe can penetrate the cell membrane and disperse uniformly in the cell with good biocompatibility. The fluorescent CNC probe with nanometer size, strong fluorescence emission and high salt-tolerance possess potential application in biomedical field. Poly(ethylene glycol)-grafted fluorescent cellulose nanocrystals were synthesized by two-step EDC/NHS-mediated coupling reaction. The fluorescent cellulose nanocrystals possessed good water-dispersibility and biocompatibility, which further improved the bioimaging performance of Hela cells. Unlabelled Image • Fluorescent dye and poly(ethylene glycol) were covalently conjugated to cellulose nanocrystals. • Good fluorescence property and water dispersibility at high salt concentration were achieved. • The fluorescent cellulose nanocrystals were successfully used for the bioimaging of Hela cells. [ABSTRACT FROM AUTHOR]

• Agricultural residue wastes can be valorized through its conversion into LCNF. • WS fibers with low lignin and ash content can be easily fibrillated to LCNF. • Post-purification treatment can further decrease lignin content and fibril diameter. • P-LCNF isolated from WS presented higher CrI and SSA values than those from WWS. Each year millions of tons of agricultural wastes are produced, however, not well utilized in China. Considering the economic development and environmental protection, the valorization of these wastes is increasingly necessary and important. Here we used p -toluenesulfonic acid hydrolysis followed by mild disk grinding for on-farm valorization of wheat straw (WS) and their pulping solid residue (waste wheat straw, WWS) to produce lignocellulosic nanofibrils (LCNF). Alkaline peroxide post-treatment was further conducted to obtain purified lignocellulosic nanofibrils (P-LCNF) with lower lignin content and thinner diameters. The raw materials and resulting LCNF and P-LCNF were investigated in each process for their chemical component, crystal structure, morphology, and thermal properties. Interestingly, although WS fiber had higher lignin content than WWS fiber, the WS fiber with lower ash content resulted in LCNF and P-LCNF with smaller height and lower thermal stability, but higher crystallinity and higher specific surface area. Higher ash content in WWS fiber protected cellulose and lignin from depolymerization and degradation, respectively, which endowed LCNF and P-LCNF with entangled network structure. Overall, this study indicated that the low-temperature fractionation process on WS and WWS fibers could yield cellulose nanomaterials with potential value-added application and achieve the efficient utilization of agricultural wastes. [ABSTRACT FROM AUTHOR]

Cellulose nanocrystals (CNCs) with high aspect ratio, ultrafine template structure and surface modifiability were used as the multifunctional support to fabricate one dimensional (1D) nanoprobe based on surface-enhanced Raman scattering spectroscopy (SERS) technology. Quaternary ammonium groups were first introduced at the hydroxyl sites on the surface of CNCs to improve the dispersion stability in aqueous solution, and then sulfhydryl groups were conjugated to the carboxyl sites through amidation. Gold nanospheres (AuNSs) were self-assembled on CNCs via strong Au-S bonds to form dense hot spots, which can easily distinguish the rhodamine (R6G) signal of six orders of magnitude when used as a SERS probe. Because the hot spots are fixed along a single CNC, the SERS signal stability and reproducibility are greatly improved compared to those of changeable hot spots formed via the irreversible aggregation of gold colloids. In addition, owing to the cationic charge repulsion effect, the nanoprobe exhibits excellent dispersion stability even in high concentration salt solutions. Considering the good sensitivity, reproducibility and dispersibility, the 1D SERS nanoprobe based on CNCs possess potential application in the field of sensing and detection in aqueous solutions. [Display omitted] • 1D "hot spots" of gold nanospheres (AuNSs) on CNC were achieved via Au-S self-assembly. • The CNC@AuNSs exhibit excellent water-dispersibility via cationic charge repulsion. • The CNC@AuNSs can be used as an ideal SERS nanoprobe with good sensitivity and stability. [ABSTRACT FROM AUTHOR]

[Display omitted] • How to construct intelligent responsive hydrogels with different nanocellulose was introduced. • The special response characteristics of nanocellulose smart hydrogel to environment were described in detail. • The application of intelligent response characteristics of nanocellulose hydrogels was summarized. Nanocellulose, with its high aspect ratio, large specific surface area, favourable modifiability, high mechanical strength, renewability, and biodegradability, has attracted significant attention over the last decade. Nanocellulose hydrogels are composite porous materials combining nanocellulose and a polymer, and they exhibit excellent water retention and mechanical properties. Stimuli-responsive nanocellulose hydrogels are not only environment-friendly but also exhibit specific responsiveness and detection capability to environmental stimuli; therefore, they have remarkable potential applicability in biomedicine, bionic intelligent materials, and sensing detection. This review aims to examine the latest developments in stimuli-responsive nanocellulose hydrogels, including their preparation, properties, and applications. The responsive behaviours of nanocellulose hydrogels are comprehensively discussed, including the effects of temperature, pH, ionic strength, light, redox agents, and electric and magnetic fields. This review also summarises the applications of stimuli-responsive nanocellulose hydrogels in detection, biomedicine, and soft actuators. Finally, it provides insights into the challenges and opportunities in the future. [ABSTRACT FROM AUTHOR]

Controllable and uniform loading of gold nanospheres (AuNSs) on cellulose nanocrystal (CNC) were first achieved by electrostatic adsorption self-assembly. By adjusting the size, Zeta potential, and the loading ratio of AuNSs and CNC, the particle spacing of AuNSs on CNC surface was successfully regulated. This strategy provides an easy and efficient approach to construct one dimensional (1D) "hot spots", which is a key to improve the performance of surface enhanced Raman scattering spectroscopy (SERS). When used as SERS probe, the nanohybrid of CNC@AuNSs is able to detect Rhodamine 6G at the low concentration of 5 × 10−8 g/L. Because AuNSs are fixed on CNC to form stable "hot spots", the SERS reproducibility of CNC@AuNSs is significantly improved compared to that of colloidal gold nanoparticles, which generally form unstable "hot spots" via irreversible aggregation. This type of multifunctional nanoprobe based on CNC has potential applications in the field of sensing detection. [ABSTRACT FROM AUTHOR]