Polyelectrolyte complex formation of alginate and chito oligosaccharide is influenced by their proportion and alginate molecular weight

Sodium alginate (SA) and chito oligosaccharide (COS) are widely used food additives in the food industry, and exploring their interaction to form polyelectrolyte complexes (PECs) may provide insights into food development. In the present study, the effects of viscosity-average molecular weight (Mv) and relative amounts of SA on the formation of sodium alginate/chito oligosaccharide polyelectrolyte (SCP) complexes were investigated. The results showed that the electrostatic interaction between -COOH and -NH2 and the hydrogen bonding between OH, were attributed to the formation of the SCP complexes. Then the formation and properties of SCP complexes were greatly dependent on the Mv and the relative amount of SA. SA with Mv of ≥2.16 × 106 Da could form spherical SCP complexes, while the SA/COS ratio (w/w) ≥ 0.8 was not conducive to the formation of SCP complexes. Moreover, the SCP complexes were more stable in the gastric environment than in the intestinal condition. In addition, 1.73 × 107 Da was the optimal Mv of SA for SCP complexes formation. This study contributed to a comprehensive understanding of the interaction between SA and COS, and shed light on the potential application of SA and COS formulation to develop new food products.

Laccase immobilization in polyelectrolyte multilayer membranes for 17α-ethynylestradiol removal: Biocatalytic approach for pharmaceuticals degradation

Enzymatic membrane reactors equipped with multifunctional biocatalytic membranes are promising and sustainable alternatives for removal of micropollutants, including steroid estrogens, under mild conditions. Thus, in this study an effort was made to produce novel multifunctional biocatalytic polyelectrolyte multilayer membranes via polyelectrolyte layer-by-layer assembly with laccase enzyme immobilized between or into polyelectrolyte layers. In this study, multifunctional biocatalytic membranes are considered as systems composed of commercially available filtration membrane modified by polyelectrolytes and immobilized enzymes, which are produced for complex treatment of water pollutants. The multifunctionality of the proposed systems is related to the fact that these membranes are capable of micropollutants removal via simultaneous catalytic conversion, membrane adsorption and membrane rejection making remediation process more complex, however, also more efficient. Briefly, cationic poly-l-lysine and polyethylenimine as well as anionic poly(sodium 4-styrenesulfonate) polyelectrolytes were deposited onto NP010 nanofiltration and UFX5 ultrafiltration membranes to produce systems for removal of 17α-ethynylestradiol. Images from scanning electron microscopy confirm effective enzyme deposition, whereas results of zeta potential measurements indicate introduction of positive charge onto the membranes. Based on preliminary results, four membranes with over 70%, activity retention produced using polyethylenimine in internal and entrapped mode, were selected for degradation tests. Systems based on UFX5 membrane allowed over 60% 17α-ethynylestradiol removal within 100 min, whereas NP010-based systems removed over 75% of estrogen within 150 min. Further, around 80% removal of 17α-ethynylestradiol was possible from the solutions at concentration up to 0.1 mg/L at pH ranging from 4 to 6 and at the pressure up to 3 bar, indicating high activity of the immobilized laccase over wide range of process conditions. Produced systems exhibited also great long-term stability followed by limited enzyme elution from the membrane. Finally, removal of over 70% and 60% of 17α-ethynylestradiol, respectively by NP010 and UFX5 systems after 8 cycles of repeated use indicate high reusability potential of the systems and suggest their practical application in removal of micropollutants, including estrogens.

Immobilization of Urease onto Nanochitosan Enhanced the Enzyme Efficiency: Biophysical Studies and in Vitro Clinical Application on Nephropathy Diabetic Iraqi Patients

Immobilization of enzymes is an effective method for improving the properties and applications of modern enzymes. There are several supports for enzyme immobilization. Because of its unique features, such as inertness and high surface area, chitosan was widely used to immobilize enzymes. Immobilization of urease onto chitosan is a promising approach to treating high urea levels in the blood, however, the immobilization conditions for the best kinetics and enzyme efficiency are still challenging. Herein, we tried to immobilize urease onto nanochitosan (chitosan NPs) through a cross-linker and study the kinetics (km and $v_{\max }$ values) and thermodynamics (Ea, ∆H, ∆S, and ∆G) parameters of the enzyme reaction before and after immobilization at different substrate concentration (50, 100, 150, 200, and 250 mg/dl) and incubation temperature (15, 20, 25, 30, 35, and 40°C) under selected optimum conditions. The immobilized urease chitosan NPs was characterized in our previous work using Fourier transform infrared $\text{infrared}$ (FTIR), Atomic force $\text{force}$ microscopy (AFM), and $\text{and}$ imaged here by scanning electron microscopy $\text{microscopy}$ (SEM). Results revealed that the highest efficiency % of immobilization (70.38%) was observed at 750 mg/ml chitosan NPs and phosphate buffer pH 7 at 40°C. With an increase of Km value for the immobilized enzyme, however, the efficiency of the enzyme was significantly higher than the free enzyme, $p<0.001$ . In addition, the activation energy of the reaction catalyzed by the immobilized enzyme was lower than that of the free enzyme, which suggests that the active site geometry of the immobilized enzyme was more favorable to accommodate the substrate and thus required less energy than that of the free enzyme. The reaction was endothermic by means of positive ∆H. The immobilized urease enzyme was in vitro applied to blood samples of Iraq nephropathy diabetic patients (n = 35) to investigate the effect on serum urease activity and urea level compared to healthy volunteers. Interestingly, the activity of serum urease significantly increased after adding the immobilized enzyme and the level of urea significantly decreased ( $p<0.0001$ ) by ∼1.5 folds. Thus, applying an immobilized urease $\text{urease}$ to remove urea from blood could be effective in the blood detoxification or dialysis regeneration system of artificial kidney machines.

Redox Sensor Array with 23.5-μm Resolution for Real-Time Imaging of Hydrogen Peroxide and Glutamate Based on Charge-Transfer-Type Potentiometric Sensor

Towards clarifying the spatio-temporal neurotransmitter distribution, potentiometric redox sensor arrays with 23.5-µm resolution were fabricated. The sensor array based on a charge-transfer-type potentiometric sensor comprises 128×128 pixels with gold electrodes deposited on the surface of pixels. The sensor output corresponding to the interfacial potential of the electrode changed logarithmically with the mixture ratio of K3Fe(CN)6 and K4Fe(CN)6, where the redox sensitivity reached 49.9 mV/dec. By employing hydrogen peroxidase as an enzyme and ferrocene as an electron mediator, the sensing characteristics for hydrogen peroxide (H2O2) were investigated. The analyses of the sensing characteristics revealed that the sensitivity was about 44.7 mV/dec., comparable to the redox sensitivity, while the limit of detection (LOD) was achieved to be 1 µM. Furthermore, the oxidation state of the electron mediator can be the key to further lowering the LOD. Then, by immobilizing oxidizing enzyme for H2O2 and glutamate oxidase, glutamate (Glu) measurements were conducted. As a result, similar sensitivity and LOD to those of H2O2 were obtained. Finally, the real-time distribution of 1 µM Glu was visualized, demonstrating the feasibility of our device as a high-resolution bioimaging technique.

Synthesis of Alginate-Chitosan Polyelectrolyte Complex (PEC) Membrane and Its Physical-Mechanical Properties

Synthesis of alginate-chitosan polyelectrolyte membrane and the determination of the physical-mechanical properties were carried out. Alginate-chitosan polyelectrolyte complex membrane can be made by mixing hydrosol alginate and chitosan hydrosol with a ratio of 1: 1 at pH 5.28. Membranes of alginate-chitosan polyelectrolyte complexes produced have physical-mechanical properties including load, elongation and elasticity, water absorption and resistance better than the constituent polymers. The results of FTIR spectroscopy analysis showed that there was an electrostatic interaction between alginate and chitosan through protonated amine groups of chitosan and carboxylic groups from alginate. Surface analyses by SEM showed that morphology of alginate-chitosan polyelectrolyte complex membrane was different with single membrane morphology

Enzyme and Mediator-coadsorbed Carbon Felt Electrode for Electrochemical Detection of Glucose Covered with Polymer Layers Based on Layer-by-Layer Technique

Glucose dehydrogenase (GlDH) and ferrocene were coadsorbed on a carbon felt (CF) sheet (5 × 10 mm, 2 mm thickness), which was used to construct an electrode for the electrochemical detection of glucose. A potential of +0.3 V vs. Ag/AgCl was applied on the base CF, and the current was measured. After the addition of glucose, the current increased and reached a steady state within 50 s. The current response was proportional to the glucose concentration up to 20 μM, with a lower detection limit of 1 μM. The surface of the CF electrode was covered by layers of polystyrene sulfonate and poly-L-lysine using layer-by-layer technique. Again the current response was proportional to glucose concentration up to 20 μM, with a lower detection limit of 2 μM. The oxidation current owing to electrochemical interferents such as L-ascorbate and acetaminophen was 1/8 times of the current observed on the unprotected electrode. In addition, the protection imparted stability to the electrode. Our work demonstrates that a GlDH/ferrocene CF electrode, protected with polystyrene sulfonate and poly-L-lysine, could be used for the electrochemical detection of glucose.

Supporting materials that improve the stability of enzyme membranes

Long-term stability is a key property of enzyme membranes that can be used for biosensors, bioreactors, and bio-fuel cells. This review discusses factors that decrease the stability, and provides two examples of enzyme membranes, a polyion complex membrane and a cellulose membrane, with which stability loss can be avoided. By using these materials, long-term stability was improved. These supporting materials could be applied to construct biosensors, bioreactors, and bio-fuel cells.

Long-Term Stability of a Cellulose-Based Glucose Oxidase Membrane

A cellulose-based glucose oxidase membrane was prepared on a glassy carbon (GC) electrode. The current response of the electrode to glucose was measured by applying a potential of 1.0 V vs. Ag/AgCl on the base GC and was proportional to the concentration of glucose up to 1 mM. The long-term stability of the electrode was examined by measuring the daily glucose response. Over four months, the response magnitude was maintained and then gradually decreased. After 11 months, though the response magnitude decreased to 50% of the initial value, the linear response range did not change. Therefore, the electrode could be used as a glucose biosensor even after 11 months of use. The entrapment of the enzyme in the cellulose matrix promoted the stability of the enzyme, as revealed by data on the enzyme activity after the enzyme electrode was immersed in urea. Therefore, the cellulose matrix may be used to improve the performance of biosensors, bioreactors and bio-fuel cells.