Electrochemical sensing of Staphylococcus aureus based on conductive anti-fouling interface.

A system for the rapid and ultra-sensitive detection of Staphylococcus aureus (S. aureus), a prevalent foodborne pathogen is introduced. Limitations of typical electrochemical sensing, often subjected to interference from non-specific protein adsorption are addressed. A dual-aptamer-based sandwich immunobiosensor is shown for its benefits regarding specificity and anti-fouling capacity, endowed by a sulfonated polyaniline layer combined with signal amplification via highly conductive gold nanoparticles. EIS spectra (Nyquist plots) were recorded at pH 7.4 PBS containing 5 mM Fe(CN)63-/Fe(CN)64-, in order to verify the possibility of the electrochemical sensing for detection of S. aureus. Results demonstrated that the constructed immunobiosensor presents an extended detection range (1 × 101 to 1 × 105 CFU/mL) and detection limit as low as 2 CFU/mL. The resistance values of the immunobiosensor developed  maintain at a stable value during 2 weeks.  Besides, the specificity of the system is highlighted by testing raw milk, and the results of which demonstrate the excellent prospects of the system for monitoring foodborne pathogens.

Biodegradable, Flexible and Ultraviolet Blocking Nanocellulose Composite Film Incorporated with Lignin Nanoparticles.

The exploration of functional films using sustainable cellulose-based materials to replace plastics has been of much interest. In this work, two kinds of lignin nanoparticles (LNPs) were mixed with cellulose nanofibrils (CNFs) for the fabrication of composite films with biodegradable, flexible and ultraviolet blocking performances. LNPs isolated from p-toluenesulfonic acid hydrolysis was easily recondensed and deposited on the surface of composite film, resulting in a more uneven surface; however, the composite film consisting of CNFs and LNPs isolated from maleic acid hydrolysis exhibited a homogeneous surface. Compared to pure CNF film, the composite CNF/LNP films exhibited higher physical properties (tensile strength of 164 MPa and Young's modulus of 8.0 GPa), a higher maximal weight loss temperature of 310 °C, and a perfect UVB blocking performance of 95.2%. Meanwhile, the composite film had a lower environmental impact as it could be rapidly biodegraded in soil and manmade seawater. Overall, our results open new avenues for the utilization of lignin nanoparticles in biopolymer composites to produce functional and biodegradable film as a promising alternative to petrochemical plastics.

Valorization of Rice Straw via Hydrotropic Lignin Extraction and Its Characterization.

Rice straw hydrotropic lignin was extracted from p-Toluene sulfonic acid (p-TsOH) fractionation with a different combined delignification factor (CDF). Hydrotropic lignin characterization was systematically investigated, and alkaline lignin was also studied for the contrast. Results showed that the hydrotropic rice straw lignin particle was in nanometer scopes. Compared with alkaline lignin, the hydrotropic lignin had greater molecular weight. NMR analysis showed that ß-aryl ether linkage was well preserved at low severities, and the unsaturation in the side chain of hydrotropic lignin was high. H units and G units were preferentially degraded and subsequently condensed at high severity. High severity also resulted in the cleavage of part ß-aryl ether linkage. 31P-NMR showed the decrease in aliphatic hydroxyl groups and the increasing carboxyl group content at high severity. The maximum weight loss temperature of the hydrotropic lignin was in the range of 330-350 °C, higher than the alkaline lignin, and the glass conversion temperature (Tg) of the hydrotropic lignin was in the range of 107-125 °C, lower than that of the alkaline lignin. The hydrotropic lignin has high ß-aryl ether linkage content, high activity, nanoscale particle size, and low Tg, which is beneficial for its further valorization.

Resource utilization and ionization modification of waste starch from the recycling process of old corrugated cardboard paper.

Generally, the mechanical strength and stiffness of old corrugated cardboard (OCC) waste paper are decreased after multiple recycling procedures. Surface sizing starch, which is extensively used in the surface sizing of paper making, accumulates after dissolving from the fibers and is transformed into pollutant during the OCC re-pulping process. To overcome the pollution and reutilization problem of the waste starch during the recycling process of OCC paper, waste starch was ionized using hydrogen peroxide (H2O2) to improve the mechanical properties of OCC paper during the reutilization. The results showed that the carboxyl group of waste starch increased with an increasing degree of ionization, resulting in enhanced copper ion adsorption capacity. Furthermore, the retention rate of the modified starch in the wet-end increased from 18.0% to 48.2%. The OCC paper presented the highest burst index and tensile strength of 8.94 kPa m2/g and 112.5 N m/g, respectively, when MS-2 was added. This work has great significance for implementation of the cleaning production of OCC waste papers and the reutilization of the waste starch.

Electrochemical sensing of lead(II) by differential pulse voltammetry using conductive polypyrrole nanoparticles.

An electrochemical sensor for Pb(II) is described that exploits (a) the outstanding adsorption ability of chitosan modified with quaternary ammonium groups (CQAS; cationic) and of lignosulfonate (LSN; anionic), and (b) the good electrical conductivity of polypyrrole nanoparticles (PPy NPs). A glassy carbon electrode (GCE) was modified with PPy NPs and polydopamine, and CQAS and LSN are used as dispersants in PPy. The modified GCE exhibits high selectivity and sensitivity for Pb(II) in the 0.1 to 50 µM concentration range, with a 55 nM detection limit (3σ method). The redox potentials for Pb(II) is around -0.55 V, and the sensor is not interfered by the presence of Hg(II) and Cu(II). The time dependent stability test showed that this sensor can maintain good reproducibility for one month. This sensor was applied to the determination of Pb(II) in wastewater samples. An electrochemical sensor for lead(II) is described that exploits the outstanding adsorption ability of chitosan that carries quaternary ammonium groups (CQAS), of lignosulfonate (LSN), and the good electrical conductivity of polypyrrole nanoparticles. CQAS and LSN are used as dispersants in PPy. The sensor exhibits high selectivity and sensitivity for Pb(II) in the range of 0.1 to 50 µM with a 55 nM detection limit.

Robust microcapsules with controlled permeability from silk fibroin reinforced with graphene oxide.

Robust and stable microcapsules are assembled from poly-amino acid-modified silk fibroin reinforced with graphene oxide flakes using layer-by-layer (LbL) assembly, based on biocompatible natural protein and carbon nanosheets. The composite microcapsules are extremely stable in acidic (pH 2.0) and basic (pH 11.5) conditions, accompanied with pH-triggered permeability, which facilitates the controllable encapsulation and release of macromolecules. Furthermore, the graphene oxide incorporated into ultrathin LbL shells induces greatly reinforced mechanical properties, with an elastic modulus which is two orders of magnitude higher than the typical values of original silk LbL shells and shows a significant, three-fold reduction in pore size. Such strong nanocomposite microcapsules can provide solid protection of encapsulated cargo under harsh conditions, indicating a promising candidate with controllable loading/unloading for drug delivery, reinforcement, and bioengineering applications.

The Effect of Fibrillation, Semi-Dry Pressing, and Surface Treatment on the Barrier Properties of Water Molecules and Oxygen on Food Packaging Paper.

The characteristics of fiber morphology and paper structure are critical to the barrier properties of food packaging paper. Herein, this study aimed to use pulp fibrillation, paper semi-dry pressing and carboxymethyl starch (CMS) coating to flatten the fibers, which were formed on the paper surface with good barrier properties due to the tight bond between fibers. The results showed that the permeability of paper was reduced by 87.56%, from 81.44 µm/Pa·s to 10.13 µm/Pa·s after the pulp fibrillation treatment (60 °SR). Moreover, semi-dry pressing treatment contributed to decreasing the water vapor transmission coefficient (WVP) by 50.98% to 2.74 × 10-10 g/m·s·Pa, and the oxygen permeation coefficient (OP) decreased by 98.04% to 1.93 × 10-14 cm3·cm/cm2·s·Pa. After coating the paper surface with titanium dioxide (TiO2) and CMS, the WVP of the paper was further reduced to 1.55 × 10-10 g/m·s·Pa, and OP was reduced to 0.19 × 10-14 cm3·cm/cm2·s·Pa. These values were 72.27% and 99.8% lower than those of the original paper, respectively. Therefore, through pulp fibrillation, semi-dry pressing of paper, TiO2 filling, and surface coating with CMS, there is no need to use synthetic polymer surface film-forming agents to achieve the high barrier properties that are required for low water and oxygen molecules permeation in food packaging paper.

Effect of Aminating Lignin Loading with Arbuscular Mycorrhizal Fungi on Soil Aggregate Structure Improvement.

Lignin is an important component of plant fiber raw materials, and is a three-dimensional network structure aromatic polymer with abundant resources and a complex structure in nature. Lignin is generally used as industrial waste, and its potential value has not been fully utilized. Modern agriculture extensively uses chemical fertilizers, leading to the gradual degradation of soil fertility and structure, which seriously affects crop growth, nutrient transport, and root respiration function. Based on soil bulk density, porosity, aggregates, and their stability indicators, this study analyzed the effects of aminated industrial lignin and its loading with arbuscular mycorrhizal fungi on soil structure improvement and plant growth. It was hoped that resource-rich lignin could play a beneficial role in improving soil structure and promoting crop growth. The phenolic hydroxyl group of lignin was epoxidized and further aminated to load with arbuscular mycorrhizal fungi. The results indicated that amine-modified lignin could effectively load with arbuscular mycorrhizal fungi. The application of arbuscular mycorrhizal fungi-supported aminated lignin to soil aggregate structure improvement greatly reduced the bulk density of soil, and increased the porosity of soil and the content of large granular soil. Compared with unmodified soil, soil bulk density decreased by 73.08%, the porosity of soil increased by 70.43%, and the content of large granular soil increased by 56.38%. Using the improved soil for corn cultivation efficiently increased the biomass of corn. The plant height was increased by 72.16%, the root-shoot ratio was increased by 156.25%, and other indexes were also improved to varying degrees. The experimental method provides an important basis for the effective utilization of lignin materials in agriculture in the future.

Comparison of hydrophobic cellulose nanofibrils modified with different diisocyanates for circulating oil absorption.

A large number of polluting substances, including chlorinated organic substances that were highly stable and hazardous, has been emitted due to the rapidly developing chemical industry, which will affect the ecological environment. Nanocellulose aerogels are effective carriers for adsorption of oil substances and organic solvents, however, the extremely strong hydrophilicity and poor mechanical properties limited their widespread applications. In this study, TEMPO-oxidized cellulose nanofibrils was modified with 2, 4-toluene diisocyanate (TDI) and 4,4'-diphenylmethane diisocyanate (MDI) to prepare strong and hydrophobic aerogels for oil adsorption. The main purpose was to evaluate and compare the effects of two diisocyanates on various properties of modified aerogels. It was found that the modified aerogel had better hydrophobic properties, mechanical properties and adsorption properties. In particular, the modified aerogel with TDI as crosslinker showed a better performance, with a maximum chloroform adsorption capacity of 99.3 g/g, a maximum water contact angle of 131.3°, and a maximum compression stress of 36.3 kPa. This study provides further evidence of the potential of functional nanocellulose aerogel in addressing environmental pollution caused by industrial emissions.

Silver Nanoparticle-Embedded Conductive Hydrogels for Electrochemical Sensing of Hydroquinone.

In this work, a conductive hydrogel was successfully synthesized, taking advantage of the high number density of active amino and hydroxyl groups in carboxymethyl chitosan and sodium carboxymethyl cellulose. These biopolymers were effectively coupled via hydrogen bonding with the nitrogen atoms of the heterocyclic rings of conductive polypyrrole. The inclusion of another biobased polymer, sodium lignosulfonate (LS), was effective to achieve highly efficient adsorption and in-situ reduction of silver ions, leading to silver nanoparticles that were embedded in the hydrogel network and used to further improve the electro-catalytic efficiency of the system. Doping of the system in the pre-gelled state led to hydrogels that could be easily attached to the electrodes. The as-prepared silver nanoparticle-embedded conductive hydrogel electrode exhibited excellent electro-catalytic activity towards hydroquinone (HQ) present in a buffer solution. At the optimum conditions, the oxidation current density peak of HQ was linear over the 0.1-100 µM concentration range, with a detection limit as low as 0.12 µM (signal-to-noise of 3). The relative standard deviation of the anodic peak current intensity was 1.37% for eight different electrodes. After one week of storage in a 0.1 M Tris-HCl buffer solution at 4 °C, the anodic peak current intensity was 93.4% of the initial current intensity. In addition, this sensor showed no interference activity, while the addition of 30 µM CC, RS, or 1 mM of different inorganic ions does not have a significant impact on the test results, enabling HQ quantification in actual water samples.

Controllable synthesis of lignin nanoparticles with antibacterial activity and analysis of its antibacterial mechanism.

As a kind of polyphenol substance, lignin is considered to have good biological activity and certain antibacterial properties. However, it is difficult to be applied because of its uneven molecular weight and difficulty in separation. In this study, by way of fractionation and antisolvent, we obtained lignin fractions with different molecular weight. Moreover, we increased the content of active functional groups and regulated microstructure of lignin, thereby increased lignin's antibacterial property. The classification of chemical components and the control of particle morphology also provided convenience for the exploration of lignin's antibacterial mechanism. The results showed that acetone with high hydrogen bonding ability could collect lignin with different molecular weights and increase the content of phenolic hydroxyl groups, up to 31.2 %. By adjusting the ratio of water/solvent (v/v) and stirring rate during the process of antisolvent, lignin nanoparticles (sphere 40-300 nm) with regular shape and uniform size can be obtained. Through observing the distribution of lignin nanoparticles in vivo and in vitro after co-incubation for different time, it could be found that lignin nanoparticles firstly damage structural integrity of bacterial cells externally, and then are swallowed into cells to affect their protein synthesis, which constitutes a dynamic antibacterial process.

Cyclic synthesis of lignin anthraquinone electrolytes for aqueous redox flow batteries.

Lignin, which is rich in phenolic hydroxyl/methoxy groups as redox active groups, is a potential electrolyte material for aqueous redox flow batteries (ARFBs). This work demonstrated to the synthesis of lignin-derived electrolytes via cyclization with 1,4-dihydroxyanthraquinone (1,4-DHAQ), in the absence of hazardous or noble metal catalysts in mild conditions (0 °C, 1 atm). The structure of lignin anthraquinone derivatives (LAQDs) cyclized in basis alkaline solution was experimentally determined. An exhaustive comparative study was conducted with respect to the electrochemical properties, charging-discharging tests and cycling performances. The initially volumetric capacitance, the capacity retention rate and coulombic efficiency of two LAQDs were determined to be 148.0 mAh.L-1, 89.3 % and 99.0 % for coniferaldehyde-anthraquinone derivative [LAQD(G)], and 132.1 mAh.L-1, 81.2 % and 99.0 % for sinusaldehyde-anthraquinone derivative [LAQD(S)], respectively. The theoretical value calculated by DFT is consistent with the actual value. Such LAQDs can be used as organic electrolyte materials, which can overcome poor chemical stability of anthraquinone, while improving the electrochemical activity of lignin-based electrolyte materials. This technology provides a pathway to prepare organic electrolyte for the development of environment friendly and better energy storage performance electrolytes for ARFBs.

ZnO microrods sandwiched between layered CNF matrix: Fabrication, stress transfer, and mechanical properties.

Functional metal oxide particles are often added to the polymers to prepare flexible functional polymer composites with adequate mechanical properties. ZnO and cellulose nanofibrils (CNF) outstand among these metal oxides and the polymer matrices respectively due to their various advantages. Herein, we in situ prepare ZnO microrods in the presence of CNF, which resultes in a layered composite structure. The ZnO microrods are sandwiched between the CNF layers and strongly bind to highly charged CNF, which provides a better stress transfer during mechanical activity. Digital image correction (DIC) and finite element analysis-based computational homogenization methods are used to investigate the relationship between mechanical properties and composite structure, and the stress transfer to the ZnO microrods. Full-field strain measurements in DIC reveal that the in situ ZnO microrods preparation leads to their homogenous distribution in the CNF matrix unlike other methods, which require external means such as ultrasonication. The computational homogenization technique provides a fairly good insight into the stress transfer between constituents in microstructure as well as a good prediction of macroscopic mechanical properties, which otherwise, would be challenging to be assessed by any ordinary mechanical testing in the layered composites. Finally, we also demonstrate that these composites could be used as physiological motion sensors for human health monitoring.

Gradience Free Nanoinsertion of Fe3O4 into Wood for Enhanced Hydrovoltaic Energy Harvesting.

Hydrovoltaic energy harvesting offers the potential to utilize enormous water energy for sustainable energy systems. Here, we report the utilization and tailoring of an intrinsic anisotropic 3D continuous microchannel structure from native wood for efficient hydrovoltaic energy harvesting by Fe3O4 nanoparticle insertion. Acetone-assisted precursor infiltration ensures the homogenous distribution of Fe ions for gradience-free Fe3O4 nanoparticle formation in wood. The Fe3O4/wood nanocomposites result in an open-circuit voltage of 63 mV and a power density of ∼52 µW/m2 (∼165 times higher than the original wood) under ambient conditions. The output voltage and power density are further increased to 1 V and ∼743 µW/m2 under 3 suns solar irradiation. The enhancement could be attributed to the increase of surface charge, nanoporosity, and photothermal effect from Fe3O4. The device exhibits a stable voltage of ∼1 V for 30 h (3 cycles of 10 h) showing good long-term stability. The methodology offers the potential for hierarchical organic-inorganic nanocomposite design for scalable and efficient ambient energy harvesting.

Design of AgNPs doped chitosan/sodium lignin sulfonate/polypyrrole films with antibacterial and endotoxin adsorption functions.

There is an urgent need to develop materials to prevent bacterial infection and the deleterious effects of endotoxins. In this study, we introduce a one-step electrodeposition method to prepare films composed of chitosan/Ag/polypyrrole and layer-by-layer self-assembly to introduce lignin sulphonate (LS) to obtain chitosan/Ag/polypyrrole/LS films. Antibacterial effects against both E. coli and S. aureus are shown by bacterial growth profiles and observation of bacteriostatic zones. Meanwhile, the addition of self-assembled LS improved the antibacterial effect of the film. For E. coli, the inhibition zone diameter was 0.93 cm, while for S. aureus, the inhibition zone diameter was 0.72 cm. Rapid and efficient endotoxin adsorption effects were shown whereby the electrostatic interactions between chitosan and endotoxin molecules played a major role. After adsorption for 1 h, in initial concentration of 1 EU/mL endotoxin solution, the adsorption efficiency could reach up to 85 %, while in initial concentration of 5 EU/mL endotoxin solution, the adsorption efficiency could reach up to 87.6 %. The results suggest chitosan/Ag/polypyrrole/LS films for their capability as a new type of antibacterial film with intrinsic endotoxin adsorption activity.

A smart gating nanocellulose membrane showing selective separation and self-cleaning performance.

A smart gating membrane based on thermal-sensitive poly (N-isopropyl acrylamide) (PNIPAM)-grafted nanocellulose and carbon nanotube (CNT) was prepared. The presence of PNIPAM shell on cellulose nanofibrils (CNFs) endow the composite membrane with thermal responsiveness. By external stimulation, an increase temperature from 10 °C to 70 °C allows the average pore size of the membrane to be controlled from 28 nm to 110 nm, as well as the water permeance from 440 L·m-2·h-1·bar-1 to 1088 L·m-2·h-1·bar-1. The gating ratio of the membrane can reach 2.47. The photothermal effect of CNT rapidly warms up the membrane to the lowest critical solution temperature in the water, avoiding the constraint that the whole water phase cannot be heated throughout the practical use process. The membrane can precisely control the nanoparticles to concentrate at 25.3 nm, 47.7 nm or 102 nm by adjust the temperature. In addition, the water permeance can be restored to 370 L·m-2·h-1·bar-1 by washing the membrane under light. The smart gating membrane has a wide application in substance multi-stage separation and selective separation, and it can realize self-cleaning.

Lignin decolorization in organic solvents and their application in natural sunscreen.

In order to improve the utilization of industrial lignin as an effective component for ultraviolet (UV) shielding, organic solvent (methanol, ethanol, and acetone) fractionation was applied to improve its UV absorption performance and reduce its apparent color. Physicochemical properties of lignin and lignin-based sunscreens, such as molar mass fraction, functional group content, color change and UV shielding properties, were characterized in detail by GPC, UV spectroscopy, 31P NMR and HSQC-NMR spectroscopy. The results showed that the color and UV-shielding properties of the soluble fraction were significantly superior to those of the original and insoluble fractions. Different lignin fractions were acted as the only active substance in the pure cream and its UV-shielding properties were compared. Among them, the composite sunscreen by adding 5 wt% acetone fractionated lignin had highest sun protection factor (SPF) value of 6.6, approximately 4.5 times higher than those sunscreens mixed with pristine lignin. Overall, this work offers the potential of industrial lignin in value-added applications such as UV protection and cosmetics.

Permeability and micromechanical properties of silk ionomer microcapsules.

We studied the pH-responsive behavior of layer-by-layer (LbL) microcapsules fabricated from silk fibroin chemically modified with different poly amino acid side chains: cationic (silk-poly L-lysine, SF-PL) or anionic (silk-poly-L-glutamic acid, SF-PG). We observed that stable ultrathin shell microcapsules can be assembled with a dramatic increase in swelling, thickness, and microroughness at extremely acidic (pH < 2.5) and basic (pH > 11.0) conditions without noticeable disintegration. These changes are accompanied by dramatic changes in shell permeability with a 2 orders of magnitude increase in the diffusion coefficient. Moreover, the silk ionomer shells undergo remarkable softening with a drop in Young's modulus by more than 1 order of magnitude due to the swelling, stretching, and increase in material porosity. The ability to control permeability and mechanical properties over a wide range for the silk-based microcapsules, with distinguishing stability under harsh environmental conditions, provides an important system for controlled loading and release and applications in bioengineering.

Improvement of Oil and Water Barrier Properties of Food Packaging Paper by Coating with Microcrystalline Wax Emulsion.

Studies have shown that fluorinated oil repellents are potentially harmful to humans and the environment, and therefore, the development of non-toxic, green, and environmentally friendly oil repellents has become inevitable. Microcrystalline wax is a branched saturated alkane with a molecular weight of 580-700 Da, which has a lower surface tension than edible oil. Herein, microcrystalline wax emulsion (fluorine-free oil repellent) was prepared by mechanical stirring-homogenization, the effects of emulsifier ratio and dosage on the emulsion performance were systematically investigated, and the resultant stable microcrystalline wax emulsions were applied to the paper surface to explore the oil and water resistance and water vapor barrier performance. The results showed that stabilized microcrystalline wax emulsion was obtained at the emulsifier Span-80/Tween-80 ratio of 5:5, and the emulsifier dosage was 20% (relative to the microcrystalline wax). When 6 g/m2 of microcrystalline wax was applied to the surface of starch pretreated paper, the kit rating value of the paper was high, at up to 10/12, the Cobb60 value decreased to 12.5 g/m2, the overall migration of paper was less than 10 mg/dm2, and the water vapor permeability was reduced by 81.9%, which met the requirements of oil and water resistance performance of food packaging paper.

Multifunctional cellulose paper-based materials and their application in complex wastewater treatment.

The rapid and efficient treatment of complex wastewater remains challenging. Herein, green paper-based materials with high wet strength, good oil-water separation property and high heavy metal ion adsorption capacity were prepared via a facile, cost-effective process. The introduction of amphoteric functional groups not only met the requirements for heavy metal ion adsorption, but also maintained the stable underwater superoleophobic properties of materials a wide pH range. The covalent crosslinking between cellulose fibers induced by polyethyleneimine and citric acid significantly improved the wet strength (up to 26.0 Nm/g) and the porosity. The membrane flux was increased up to 3515 L/(m2·h) and the separation efficiencies were higher than 98%. Moreover, the theoretical maximum adsorption capacities for Cd(II) and Pb(II) reached 73.29 and 93.75 mg/g, respectively. Combined with filtration technology, the materials can realize the continuous and efficient purification of complex wastewater.