Enhanced mechanical properties and antibacterial activities of chitosan films through incorporating zein-gallic acid conjugate stabilized cinnamon essential oil Pickering emulsion.

In this study, zein-gallic acid covalent complex prepared by alkali treatment was utilized as an emulsifier to stabilize cinnamon essential oil (CEO) Pickering emulsion, and the chitosan-based (CZGE) films loaded with CEO Pickering emulsion were prepared by blending. The influences of different contents of CEO Pickering emulsion on the physical properties and biological activities of CZGE films were investigated. The results showed that Pickering emulsion had good compatibility with chitosan matrix and enhanced the interaction between film-forming matrix polymer. In addition, incorporating with CEO Pickering emulsion (15 %, v/v) significantly improved the mechanical and barrier properties of the films, and also enhanced the light transmittance and thermal stability of the films. Furthermore, the loading of emulsion also improved the antioxidant activities of the films and led to the formation of high antimicrobial property against food pathogens, and the slow-release behavior of CEO could effectively extend the biological activity of the films. These results suggested that Pickering emulsion has potential as a loading system and a plasticizer in active packaging, and the feasibility of CZGE film in food packaging.

Preparation and characterization of functionalized chitosan/polyvinyl alcohol composite films incorporated with cinnamon essential oil as an active packaging material.

In this study, amphiphilic chitosan (NPCS-CA) was synthesized by grafting quaternary phosphonium salt and cholic acid onto the chain of chitosan, aiming to develop an active edible film based on NPCS-CA and polyvinyl alcohol (PVA) incorporated with cinnamon essential oil (CEO) by the casting method. The chemical structure of the chitosan derivative was characterized by FT-IR, 1H NMR and XRD. Through the characterization of FT-IR, TGA, mechanical and barrier properties of the composite films, the optimal proportion of NPCS-CA/PVA was determined as 5/5. And, the tensile strength and elongation at break of the NPCS-CA/PVA (5/5) film with 0.4 % CEO were 20.32 MPa and 65.73 %, respectively. The results revealed that the NPCS-CA/PVA-CEO composite films exhibited an excellent ultraviolet barrier property at 200-300 nm and significantly reduced oxygen permeability, carbon dioxide permeability and water vapor permeability. Furthermore, the antibacterial property of film-forming solutions against E. coli, S. aureus, and C. lagenarium was distinctly improved with the increase of NPCS-CA/PVA proportion. And, the multifunctional films effectively extended the shelf-life of mangoes at 25 °C based on the characterization of surface changes and quality indexes. The NPCS-CA/PVA-CEO films could be developed as biocomposite food packaging material.

Nutrient controlled release performance of bio-based coated fertilizer enhanced by synergistic effects of liquefied starch and siloxane.

The porous structure and hydrophilicity of coating shells affect the nutrient controlled-release performance of castor oil-based (CO) coated fertilizers. In order to solve these problems, in this study, the castor oil-based polyurethane (PCU) coating material was modified with liquefied starch polyol (LS) and siloxane, and a new coating material with cross-linked network structure and hydrophobic surface was synthesized, and used it to prepare the coated controlled-release urea (SSPCU). The results demonstrated that the cross-linked network formed by LS and CO improved the density and reduced the pores on the surface of the coating shells. The siloxane was grafted on the surface of coating shells to improve its hydrophobicity and thus delayed water entry. The nitrogen release experiment indicated that the synergistic effects of LS and siloxane improved the nitrogen controlled-release performance of bio-based coated fertilizers. Nutrient released longevity of SSPCU with 7 % coating percentage reached >63 days. Moreover, the nutrient release mechanism of coated fertilizer was further revealed by the analysis of the release kinetics analysis. Therefore, the results of this study provide a new idea and technical support for development of efficient and environment-friendly bio-based coated controlled-release fertilizers.

Dual-grafted dextran based nanomicelles: Higher antioxidant, anti-inflammatory and cellular uptake efficiency for quercetin.

Quercetin (QCT) has antioxidant, anti-inflammatory, anti-tumor and other important pharmacological activities, but the poor water solubility limits its application. In this work, the amphiphilic dextran (ADEX) was prepared by grafting L-cysteine and octadecylamine onto carboxymethyl dextran with the grafting rate of 21.29 % and 19.35 %. Then, the QCT-loaded nanomicelles (QNMs) were prepared by using ADEX as wall material and the QCT as core material via ultrasonic self-assembly method. The particle size and zeta potential of QNMs were 372 nm and 31.4 mV. Under simulated gastric and simulated intestinal fluids, the cumulative release QNMs were 37.54 % and 52.13 % within 180 min, and the QNMs showed better stability in simulated gastric fluid. The QNMs showed significantly better PTIO, OH and O2- scavenging activities than QCT. In addition, QNMs could effectively down-regulate the expression of pro-inflammatory cytokines and promoted the expression of anti-inflammatory cytokine. The cellular uptake results proved that the QNMs were more easily absorbed by cells than free QCT, indicating that the nano-encapsulation procedure effectively improved the uptake efficiency of QCT by cells.

Amphiphilic chitosan/carboxymethyl gellan gum composite films enriched with mustard essential oil for mango preservation.

In this paper, amphiphilic chitosan and carboxymethyl modified gellan gum were synthesized to develop an active edible fresh-keeping material. The optimal weight ratio of CMCS-g-CA/CMGG was determined as 5:2 through the characterization of Fourier transform infrared (FT-IR), Thermogravimetric analysis (TGA), mechanical and barrier properties of the composite films. In addition, the water vapor permeability and oxygen permeability of CMCS-g-CA/CMGG composite films incorporated with mustard essential oil were all declined, and the antibacterial property of the composite film solutions against E. coli, S. aureus and Bacillus anthracis was distinctly improved with the increase of mustard essential oil (MEO) dosage. Furthermore, the CMCS-g-CA/CMGG + 2.0 µL/mL MEO composite film exhibited an effective preservation on mango fruits during 20 days of storage based on the characterization of surface appearance and quality indexes of fruits. Hence, the multifunctional CMCA-g-CA/CMGG/MEO composite films can be served as a prospective eco-friendly packaging material for fruit preservation.

Synergistic antibacterial activity of chitosan modified by double antibacterial agents as coating material for fruits preservation.

Chitosan (CS) is a natural marine polysaccharide with good biocompatibility and biodegradability. But its poor water solubility and antibacterial activity limit its application in fruits preservation. In this study, based on the advantage of quaternary phosphonium salt (QP) and salicylic acid (SA) with good antibacterial activities and different antibacterial mechanisms, a novel antibacterial coating material was synthesized by grafting QP and SA onto CS. With the grafting of SA and QP onto CS, not only the crystallinity of CS molecules decreased and the water solubility improved, but also the antibacterial activity of CS-QP-SA against Escherichia coli and Staphylococcus aureus, and Colletotrichum gloeosporioides (anthracnose) improved by the synergistic effect of QP and SA. After 20 days storage, the mango fruits treated by CS-QP-SA had a weight loss rate of 12.86 %, the fruit decay incidence was 52.00 ± 1.70 %. Hence, the CS-QP-SA films effectively extending the storage time of mango fruits to a certain extent. The results of this study indicated that CS-QP-SA might be a promising preservative for fruits and vegetables.

Synthesis and characterization of carboxymethyl chitosan/epoxidized soybean oil based conjugate catalyed by UV light, and its application as drug carrier for fusarium wilt.

In this paper, a cationic photoinitiator (TAS) was used as a catalyst for the ring opening reaction of carboxymethyl chitosan (CMCS) and epoxidized soybean oil (ESO) under UV light to prepare CMCS-g-ESO conjugate, and the structure of the product was characterized by FT-IR, 1H NMR and GPC. Then, the spinosad-loaded microcapsules (SSD@CMCS-g-ESO) were prepared by ultrasonic self-assembly method. The results showed that TAS could catalyze the ring opening reaction of CMCS and ESO under UV-irradiation and the optimum reaction time was 1 h, with the molecular weight of 15,745. The average particle size of SSD@CMCS-g-ESO was about 2.16 µm, and the encapsulation efficiency (EE) and drug loading content (LC) of SSD@CMCS-g-ESO were 85.39 ± 2.05% and 20.17 ± 1.84%, respectively. In vitro release revealed that SSD@CMCS-g-ESO exhibited sustained-release and pH-responsive property, and the accumulative release in the buffer solution of pH = 6.5 and 7.4 was higher than in pH = 9.0. Furthermore, SSD@CMCS-g-ESO had a good antifungal properties against Fusarium oxysporum f. sp. cubense (Foc) compared with the unencapsulated SSD at the same drug dose. This work indicated that photo-chemical reactions could be used to prepare bio-based carrier materials to construct drugs delivery system for targeted treatment of fusarium wilt.

Preparation and characterization of chitosan derivatives modified with quaternary ammonium salt and quaternary phosphate salt and its effect on tropical fruit preservation.

In this paper, HACC modified with (5-Carboxypentyl) (triphenyl) phosphonium bromide (HA-CS-NP) was synthesized. Then, a multifunctional food packaging composite film with good thermal stability and antibacterial functions was fabricated by HA-CS-NP and poly (vinyl alcohol) (PVA). The tensile strength and elongation at break of HA-CS-NP/PVA composite film at the weight ratio of 3/7 were 20.32 ± 1.02 MPa and 65.73 ± 3.29%, respectively. And, the inhibition rates of HA-CS-NP (0.5%) on Mango C. lagenarium and Papaya C. gloeosporioides on day 6 were up to 80.92 ± 4.12%. Compared with CK group, the weight loss of experimental groups were 23.96 ± 2.46 g/206 ± 7.25 g (mangoes) and 59.45 ± 3.06 g/496 ± 6.37 g (papaya), reduced by 35.76 ± 1.15%. Moreover, the final hardness value of the fruits coated with composite films was 4.94 ± 0.23 kg/cm3 and increased by 20.79 ± 1.04%, and the rot index was reduced by 71.43 ± 3.24%. The multifunctional HA-CS-NP/PVA coating has broad prospects in the application of food packaging.

Preparation of zinc phthalocyanine-loaded amphiphilic phosphonium chitosan nanomicelles for enhancement of photodynamic therapy efficacy.

To increase the solubility and the encapsulation of zinc phthalocyanine (ZnPc) photosensitizer for photodynamic therapy (PDT), a positively charged amphiphilic phosphonium chitosan nanomicelle with multi-benzene structure was developed, and its application to PDT was explored. N-acetyl-l-phenylalanine-(4-carboxybutyl) triphenylphosphonium bromide chitosan (CTPB-CS-NAP), a chitosan derivative with tunable amphiphilicity, was synthesized first. ZnPc was encapsulated in CTPB-CS-NAP at the critical micelle concentration (CMC) of 4.898 mg/L by a hydrophobic self-assembly method to form ZnPc-loaded nanomicelles (ZnPc@CTPB-CS-NAP). The method gives the highest encapsulation efficiency and drug loading of 89.4 % and 22.3 %, respectively. ZnPc@CTPB-CS-NAP is stably dispersed in aqueous solution and shows the average particle size of 103±5 nm. PDT experiments suggest the phototoxicity of ZnPc@CTPB-CS-NAP is much higher than that of ZnPc, but no obvious dark cytotoxicity is observed. Our study has provided a new strategy for improving the photodynamic therapy efficacy of hydrophobic photosensitizer by the encapsulation with chitosan derivative carriers.

Construction of pH/glutathione responsive chitosan nanoparticles by a self-assembly/self-crosslinking method for photodynamic therapy.

A novel pH/glutathione (GSH) multi-responsive chitosan nanoparticles (NPs) material has been successfully designed and prepared by a self-assembly/self-crosslinking method for photodynamic therapy (PDT), which overcomes the shortcomings of traditional photosensitizer carriers, such as poor chemical stability, low loading efficiency and single-responsive photosensitizer release. Amphiphilic sulfhydryl chitosan (SA-CS-NAC) is first prepared by modifying chitosan (CS) with stearic acid (SA) and N-acetyl-L-cysteine (NAC), and then subject to self-assembly and self-crosslinking in the presence of photosensitizer, indocyanine green (ICG), to form the ICG-loaded amphiphilic sulfhydryl chitosan nanoparticles (SA-CS-NAC@ICG NPs). The ICG entrapment efficiency and loading efficiency of the NPs are found to be 95.2% and 27.6%, respectively. The multi-responsive ICG release of the NPs to the low pH and high GSH content of the microenvironment in tumor cells is successfully achieved. Under the laser irradiation, the SA-CS-NAC@ICG NPs produce the amount of reactive oxygen species (ROS) twice of that generated by free ICG under the same conditions. The in vitro cell experiment confirmed the strong cellular uptake ability, low biotoxicity and good tumor inhibition of the NPs. Our work has provided a new strategy for the targeted photosensitizer delivery for PDT.

Dual drug delivery system of photothermal-sensitive carboxymethyl chitosan nanosphere for photothermal-chemotherapy.

Aiming at high drug loading and controlled drug release in chitosan nanocarriers, this work constructed the photothermal sensitive carboxymethyl chitosan nanospheres carrier by introducing controllable heat-sensitive groups into carboxymethyl chitosan molecules. The combination therapy system based on photothermal-chemotherapy was established by virtue of the good photothermal conversion effect of ICG and the high chemotherapy efficiency of DOX. On the one hand, the carrier owned high drug loading and improved the stability of coated-drug. On the other hand, the nanospheres generated photothermal response through NIR irradiation to improve the drug release amount and to achieve the combined treatment effect of photodynamic therapy and chemotherapy. The structures of the nanospheres were fully characterized by Fourier transform infrared (FT-IR), nuclear magnetic resonance (1H NMR) and scanning electron microscope (SEM). In vitro photothermal tests proved that the nanospheres had excellent light stability and photothermal conversion performance. The cytotoxicity test results showed that the nanospheres had no obvious toxicity, but the drug-loaded nanospheres could effectively inhibit the growth of HepG-2 cells via photo-response to release DOX and ICG for achieving photothermal-chemotherapy under NIR irradiation.

Self-assembled amphiphilic chitosan nanomicelles to enhance the solubility of quercetin for efficient delivery.

Quercetin (QCT) has important functions such as antioxidant, anti-inflammatory and anticancer. However, its applications in food and in drug are restricted owing to its poor water solubility. In this work, a novel amphiphilic wall-material chitosan was synthesized via grafting of chitosan with deoxycholic acid (DA) as hydrophobic group and modified N-acetyl-L-cysteine (NAC) as hydrophilic group. Amphiphilic chitosan was self-assembled to load QCT as nanomicelles by a low-cost and inorganic solvent procedure. Both the encapsulation efficiencies (EE) and drug-loading rates (DL) increased when increasing the grafting rate of DA. There was a bursting release of QCT for the QCT-loaded nanomicelles (CS-DA-NAC-QNMs) from 0 to 8 h, and then the release rate decreased gradually. After releasing for 72 h, the final cumulative release percentages were more than 40%. All the QCT-loaded nanomicelles samples showed good hemocompatibility, and their water solubility and biocompatibility increased evidently. What's more, they exhibited an obvious inhibition rate of A549 cells.

A dual-signal readout enzyme-free immunosensor based on hybridization chain reaction-assisted formation of copper nanoparticles for the detection of microcystin-LR.

Enzyme-based electrochemical biosensors are widely used in immunoassays, but the intrinsic disadvantages of enzymes including instability or sensitivity to temperature and pH should be considered. Herein, an enzyme-free and dual-signal readout immunoassay was established to detect microcystin-LR (MC-LR) sensitively and selectively. Firstly, the microplate was modified with gold nanoparticles-decorated-carbon nanotubes (AuNP-CNT) to immobilize sufficient antigens by the high surface area of CNT and high affinity of AuNP. Then, silver nanoparticles were decorated on gold nanorods to form corn-like AgNP/AuNR composite and then capture secondary antibody and initiator DNA strand. After hybridization chain reaction, long double helix DNA strands can be formed on AgNP/AuNR to germinate copper nanoparticles. A dual-signal readout from the current responses of both silver and copper ions was obtained by using differential pulse stripping voltammetry with the aid of acid-treatment. By using a competitive immunoreaction, MC-LR can be detected in a linear range from 0.005 µg/L to 20 µg/L with a lower detection limit of 2.8 ng/L. The reproducibility, stability and specificity were all acceptable, indicating its promising application in environment monitoring and sensitive electrochemical detection for other analytes.

Multiple amplified enzyme-free electrochemical immunosensor based on G-quadruplex/hemin functionalized mesoporous silica with redox-active intercalators for microcystin-LR detection.

A novel multiple amplified enzyme-free immunosensor was developed for competitive immunoassay of microcystin-LR (MC-LR). Classical electrochemical immunosensors usually employ enzymes as biocatalysts to afford amplified signals, but the proteolytic degradation and poor stability are still crucial problem. Herein, monodisperse core-shell mesoporous silica (SiO2@MSN)-functionalized DNAzyme concatamers were synthesized to load hemin and methylene blue (MB) as the mimic enzyme. Firstly, the surface of SiO2@MSN was conjugated with secondary antibody as the recognition of MC-LR antibody and with a DNA strand as the initiator. Two auxiliary DNA strands were then selected for the in-situ propagation to form a double-helix DNA through hybridization chain reaction (HCR), forming numerous DNAzymes (G-quadruplex/hemin) after the addition of hemin. Secondly, MB was inserted into the formed double-helix DNA, and also loaded in the brush-like structure of mesoporous SiO2@MSN. The molecular docking study showed that electrons can transfer more effectively with π-π stack of hemin/G-quadruplex and intercalation of MB/DNA, thus the catalytic ability of DNAzymes can be greatly improved. With the aid of MB, DNAzymes can catalyze the reduction of H2O2 to produce the electrochemical signal. This enzyme-free electrochemical immunosensor can successfully detect MC-LR in a range of 0.5ng/L and 25µg/L with a detection limit of 0.3ng/L. This stable, sensitive and selective nonenzymatic electrochemical immunoassay shows promise for applications in food and environmental monitoring.

In-situ assembly of biocompatible core-shell hierarchical nanostructures sensitized immunosensor for microcystin-LR detection.

Microcystin-LR (MC-LR) is a kind of hepatotoxin which can cause functional and structural disturbances of the liver, accumulate in aquatic organisms and transfer to higher trophic levels, a biocompatible electrochemical immunosensor was constructed to detect MC-LR sensitively and selectively. The three-dimensional villiform-like carbon nanotube/cobalt silicate (CNT@Co silicate) core-shell nanocomposites were synthesized and firstly used as the substrate to immobilize the antigen of MC-LR (Ag), while Fe3O4 nanoclusters/polydopamine/gold nanoparticles (Fe3O4@PDA-Au) core-shell magnetic nanocomposites were prepared as the label carrier of the immunosensor to conjugate the second antibody (Ab2) and horse radish peroxidase (HRP). Since the toxicity of nanomaterials is important in the construction of biosensors including the immobilization of antigen or antibody, the biocompatibility of such nanocomposites were investigated by monitoring the cell viability after culturing with Hela cells. Due to the excellent biocompatibility, the immunosensor can immobilize more antigens by the large surface area of the three-dimensional villiform-like structure in CNT@Co silicate, and provide high electrochemical signals by Fe3O4@PDA-Au labeled Ab2 and HRP. After investigation of the binding capability of biomolecules on nanomaterials and optimization of the conditions in the competitive immunoassay, the proposed electrochemical immunosensor shows a linear response to MC-LR in the range from 0.005 µg/L to 50 µg/L with a detection limit of 0.004 µg/L. In addition, the specificity, reproducibility and stability of the immunosensor were also proved to be acceptable, indicating its potential application in environmental monitoring.

A multi-walled carbon nanotubes-poly(L-lysine) modified enantioselective immunosensor for ofloxacin by using multi-enzyme-labeled gold nanoflower as signal enhancer.

The enantioselective detection of trace amounts of ofloxacin is very important in many fields. In this work, an enantioselective and sensitive electrochemical immunosensor was constructed for the detection of chiral antibiotic ofloxacin based on a dual amplification strategy using multiwall carbon nanotubes-poly(L-lysine) as a matrix to immobilize the antigen and multi-enzyme-antibody functionalized gold nanoflowers as an electrochemical detection label. The fabrication process of the dual-amplified immunosensor was characterized by scanning electron microscopy, cyclic voltammogram and electrochemical impedance spectroscopy, respectively. After the optimization of the experimental conditions, a competitive immunoassay, i.e., the association ability with the corresponding antibody between the captured antigen and free S-OFL or R-OFL in the solution, showed that the immunosensor exhibited a sensitive response to S-OFL in the range from 0.26 to 25.6 ng/mL with a detection limit of 0.15 ng/mL as well as a sensitive response to R-OFL in the range from 0.37 to 12.8 ng/mL with a detection limit of 0.30 ng/mL. Along with the acceptable sensitivity and stability, the S-OFL or R-OFL immunosensor showed selective ability to its corresponding enantiomer, suggesting this amplification strategy may hold a potential application in the detection of OFL in food or environment.