Preparation, Properties and Mechanism of Inhomogeneous Calcium Alginate Ion Cross-linking Gel Microspheres

Inhomogeneous calcium alginate ion cross-linking gel microspheres,a novel ion absorbent,were prepared by dropping a sodium alginate solution to a calcium chloride solutioin via an electronic droplet generator.Calcium alginate microspheres have uniform particle sizes.a smooth surface and a microporous structure.The electrode probe reveals the inhomogeneous distribution of calcium ions with the highest concentration on the surface,and the lowest concentration in the cores of the spheres.As a novel ion adsorbent,calcium alginate gel microspheres have a lower limiting adsorption mass concentration,a higher enrichment capacity and a higher adsorption capacity for Pb^2 than usual ion exchange resins.The highest percentage of the adsorption is 99.79%.The limiting adsorption mass concentration is 0.0426mg/L.The adsorption capacity for Pb^2 is 644mg/g,Calcium alginate gel microspheres have a much faster ion exchange velocity than D418 chelating resin and D113 polyacrylate resin.The moving boundary model was employed to interpret the ion exchange kinetics process,which indicates that the ion exchange process is controlled by intraparticle diffusion of adsorbable ions.So the formation of inhomogeneous gel microspheres reduces the diffusion distance of adsorbable ions within the spheres and enhances the ion exchange velocity.Alginate has a higher selectivity for pb^2 than for Ca^2 and the selectivity coefficient KCa^Pb is 316. As an ion cross-linking gel,calcium alginate inhomogeneous microspheres can effectively adsorb heavy metal Pb^2 at a higher selectivity and a higher adsorption velocity.It is a novel and good ion adsorbent.     

Shape-controlled production of biodegradable calcium alginate gel microparticles using a novel microfluidic device

In this paper we describe a novel method of manufacturing shape-controlled calcium alginate gel microparticles in a microfluidic device. Both manufacturing shape-controlled microparticles and synthesizing hydrogel microparticles could be performed simultaneously in the microfluidic device. The novel microfluidic device comprised of two individual flow-focusing channels and a synthesizing channel was successfully applied as a continuous microfluidic reactor to synthesize gel microparticles with size and shape control. By passive control based on the microchannel geometric confinement and liquid-phase flow rates, we succeeded in producing monodisperse sodium alginate microparticles with diverse shapes (such as plugs, disks, microspheres, rods, and threads) in the flow-focusing channels of the microfluidic device. The shape and size of the sodium alginate microparticles could be tuned by adjusting the flow rates of the various streams. Further stages of the chemical reaction could be initiated by mixing sodium alginate microparticles and calcium chloride (CaCl2) solution in the synthesizing channel. The shapes of the sodium alginate microparticles could be permanently preserved by the synthesis of calcium alginate gel microparticles. The preparation conditions of size- and shape-controlled calcium alginate microparticles and influence factors were studied.     

Fabrication of organic phase biosensors based on multilayered polyphenol oxidase protected by an alginate coating

We describe herein, the creation of an organic phase enzyme electrode (OPEE) via avidin–biotin interactions built over an electrogenerated polymer. Multilayered polyphenol oxidase (PPO) assemblies were transferred into an organic solvent (chloroform) for the catechol detection at −0.2 V. In conjunction with an alginate gel, as a hydrophilic additive, the biosensor performance was widely enhanced. The effects of biotinylated polypyrrole film and alginate gel on the diffusion process through the biosensor coating are studied by rotating disk electrode experiments carried out in chloroform with hydroquinone as electroactive permeant.     

以铜离子为模板的褐藻酸凝胶对铜离子的选择性富集研究

以铜离子为模板，制备了褐藻酸凝胶（Cu-alginate)，通过吸附实验及过柱渗滤实验，试验了该吸附剂对铜离子的选择性吸附性能，并且采用该吸附剂富集了自来水中微量的Cu^2 ，结合原子吸收法测定了水样中Cu^2 的含量。结果表明：该吸附剂对Cu^2 有较高的选择性吸附性能，显著优于一些化学合成铜离子模板缩聚物及非铜模板褐藻酸凝胶（如Ca-alginate),非重金属离子（如K^ 、Na^ 、Ca^2 ）及某些重金属离子（如Ni^2 、Cd^2 ）等对Cu^2 的吸附均不产生明显干扰。用该吸附剂富集水中的微量铜离子，回收率可达97.7%。     

Urease–glutamic dehydrogenase biosensor for screening heavy metals in water and soil samples

A screen-printed three-electrode amperometric biosensor based on urease and the nicotinamide adenine dinucleotide hydrogen (NADH)–glutamic dehydrogenase system was developed and applied to the screening of heavy metals in environmental samples. The development of an amperometric sensor for the monitoring of urease activity was feasible by coupling the urea breakdown reaction catalysed by urease to the reductive ammination of ketoglutarate catalysed by glutamic dehydrogenase (GLDH). The ammonia provided by the urea conversion is required for the conversion of ketoglutarate to glutamate with the concomitant oxidation of the NADH cofactor. NADH oxidation is monitored amperometrically at 0.3 V (vs. Ag/AgCl) after urease immobilization onto the screen-printed three-electrode configuration. Immobilization of urease on the surface of screen-printed electrodes was performed by entrapment in alginate gel and adsorption on the electrode in a nafion film. Low sensitivity to inactivation by metals was recorded after urease entrapment in alginate gel with detection limits of 2.9 and 29.8 mg L^–1 for Hg(II) and Cu(II), respectively. The use of the negatively charged nafion film created a more concentrated environment of cations in proximity to the enzyme, thus enhancing the urease inhibition when compared to gel entrapment. The calculated detection limits were 63.6 and 55.3 g L^–1 for Hg(II) and Cu(II), respectively, and 4.3 mg L^–1 for Cd(II). A significant urease inactivation was recorded in the presence of trace amounts of metals (g L^–1) when the enzyme was used free in solution. Analysis of water and soil samples with the developed nafion-based sensor produced inhibition on urease activity according to their metal contents. The obtained results were in agreement with the standard methods employed for sample analysis. Nevertheless, the use of the amperometric assay (with free urease) proved more feasible for the screening of trace amounts of metals in polluted samples.     

Light-activated ionic gelation of common biopolymers

Biopolymers such as alginate and pectin are well known for their ability to undergo gelation upon addition of multivalent cations such as calcium (Ca(2+)). Here, we report a simple way to activate such ionic gelation by UV irradiation. Our approach involves combining an insoluble salt of the cation (e.g., calcium carbonate, CaCO(3)) with an aqueous solution of the polymer (e.g., alginate) along with a third component, a photoacid generator (PAG). Upon UV irradiation, the PAG dissociates to release H(+) ions, which react with the CaCO(3) to generate free Ca(2+). In turn, the Ca(2+) ions cross-link the alginate chains into a physical network, thereby resulting in a hydrogel. Dynamic rheological experiments confirm the elastic character of the alginate gel, and the gel modulus is shown to be tunable via the irradiation time as well as the PAG and alginate concentrations. The above approach is easily extended to other biopolymers such as pectin. Using this approach, a photoresponse can be imparted to conventional biopolymers without the need for any chemical modification of the molecules. Photoresponsive alginate gels may be useful in creating biomaterials or tissue mimics. As a step toward potential applications, we demonstrate the ability to photopattern a thin film of alginate gel onto a glass substrate under mild conditions.     

Facile preparation of ferromagnetic alginate-g-poly(vinyl alcohol) microparticles

Alginate-g-poly(vinyl alcohol) was physically cross-linked with Fe(II) ion in a surfactant-free emulsion system to form microparticles via in situ precipitation. The microparticles were subjected to oxidation in aqueous of pH 13 at ambient temperature and transformed into magnetic ones within minutes. X-ray diffractometry showed that magnetic Fe₃O₄ was formed and it was further confirmed with a vibrating sample magnetometer measurement. Scanning electron microscopy examinations indicated that the iron oxide was well embedded into ferrous alginate and the size of particles was around 0.2-1.2 μm.     

Entrapment of Lentinus sajor-caju into Ca-alginate gel beads for removal of Cd(II) ions from aqueous solution: preparation and biosorption kinetics analysis

A white rot fungus species Lentinus sajor-caju biomass was entrapped into alginate gel via a liquid curing method in the presence of Ca(II) ions. The biosorption of cadmium(II) by the entrapped live and dead fungal biomass has been studied in a batch system. The heat-treatment process enhanced the biosorption capacity of the immobilized fungal biomass. The effect of initial cadmium concentration, pH and temperature on cadmium removal has been investigated. The maximum experimental biosorption capacities for entrapped live and dead fungal mycelia of L. sajur-caju were found to be 104.8±2.7 mg Cd(II) g⁻¹ and 123.5±4.3 mg Cd(II) g⁻¹, respectively. The kinetics of cadmium biosorption was fast, approximately 85% of biosorption taking place within 30 min. The biosorption equilibrium was well described by Langmuir and Freundlich adsorption isotherms. The change in the biosorption capacity with time is found to fit pseudo-second-order equations. Cadmium binding properties of entrapped fungal preparations have been determined applying the Ruzic equations. Since the biosorption capacities are relatively high for both entrapped live and dead forms, they could be considered as suitable biosorbents for the removal of cadmium in wastewater treatment systems. The biosorbents were reused in three consecutive adsorption/desorption cycles without significant loss in the biosorption capacity.     

Hydrophobic Effects of o-Phenanthroline and 2,2′-Bipyridine on Adsorption of Metal(II) Ions onto Silica Gel Surface

The effects of o-phenanthroline and 2,2′-bipyridine on the adsorption of metal(II) (Fe, Co, Ni and Cu) ions onto silica gel surface have been studied. The adsorption is expressed in terms of the measured concentrations of both metal and ligand at equilibrium. Each adsorption of the four metal ions is increased with the presence of the ligands. In addition, adsorption increases slowly with pH at low pH values and then increases rapidly up to near the pK_a value of silica gel (≈6.5). The adsorption of each metal ion at low pH is increased with increased ligand concentration. However, at high pH the adsorptions of Fe(II) and Cu(II) are decreased with increased ligand concentration whereas the adsorptions of Co(II) and Ni(II) are always increased. At low pH values the ligand to metal ratio adsorbed on the silica gel surface is ca. 3:1 while at high pH values it is 1:1, 2:1, and 3:1, corresponding to the initial ligand to metal ion concentration ratio. The addition of ethanol to the phenanthroline-SiO₂ solution results in a decrease in the adsorption of phenanthroline. The effect of ethanol is also observed in the Fe(II)-phenanthroline-SiO₂ system. The behavior of the adsorption is interpreted qualitatively by hydrophobic expulsion, the formation of surface complexes, and electrostatic interaction. It is concluded that hydrophobic expulsion plays an important role in the adsorption of metal ions in the presence of hydrophobic ligands on silica gel surface.     

Competitive adsorption of Ca2+ and Zn(II) ions at monodispersed SiO2/electrolyte solution interface

A study of competitive adsorption of Ca(2+) and Zn(II) ions at the monodispersed SiO(2)/electrolyte solution interface is presented. Influence of ionic strength, pH, and presence of other ions on adsorption of Ca(2+) and Zn(II) in the mentioned system are investigated. zeta potential, surface charge density, adsorption density, pH(50%), and DeltapH(10-90%) parameters for different concentrations of carrying electrolyte and adsorbed ions are also presented. A high concentration of zinc ions shifts the adsorption edge of Ca(2+) ions adsorbed from solutions with a low initial concentration at the SiO(2)/NaClO(4) solution interface to the higher pH values. This effect disappears with a concentration increase of calcium ions. The presence of Ca(2+) ions in the system slightly affects the adsorption of zinc ions on SiO(2), shifting the adsorption edge toward lower pH values and thereby increasing the adsorption slope.     

Electrochemistry of microparticles of tris (2,2′-bipyridine) ruthenium(II) hexafluorophosphate

The electrochemical behaviour of tris(2,2′-bipyridine)ruthenium(II) hexafluorophosphate (Ru(II)) microparticles, immobilised on a graphite electrode and adjacent to an aqueous electrolyte solution, has been studied by cyclic voltammetry and an in situ spectroelectrochemical technique. The solid Ru(II) complex exhibits one reversible redox couple with a formal potential (E_f) of 1.1 V versus Ag¦AgCl. The continuous cyclic voltammetric experiments showed that the Ru(II) microparticles are stable during the electrochemical conversions. The in situ spectroelectrochemical study showed that the absorbance at 463 nm decreased due to the oxidation of Ru(II) to Ru(III). Upon reduction, the growth of absorbance at 463 nm was observed due to the formation of Ru(II) complex and this process was reversible.     

Lead(II) ion-selective electrode based on polyaminoanthraquinone particles with intrinsic conductivity

A new polyvinylchloride membrane electrode was facilely prepared by using polyaminoanthraquinone (PAAQ) microparticles with an intrinsically electrical conductivity as a lead(II) ionophore. It is found that the electrode performance will significantly be improved with adding 1 wt% PAAQ microparticles and decreasing the membrane thickness. A 90 μm-thick membrane electrode consisting of PAAQ(salt):polyvinyl chloride:dioctylphthalate:sodium tetraphenylborate of 1:33:66:1 (wt) but without any traditional lead(II) ionophore achieved the optimal performance and exhibited a good Nernstian response for Pb(II) ions over a wide concentration range from 2.5 × 10⁻⁶ to 0.1 M with a slope of 28.9 mV/decade and a detection limit down to 776 nM. A reasonably short response time of 12 s was revealed together with a long lifetime over a period of around 4 months in a wide pH range between 2.8 and 5.2. A fixed interference method indicated that the electrode has an excellent selectivity for lead(II) ion over alkali, alkaline earth and other heavy metal ions. The proposed electrode has been also found to be a powerful indicator electrode for potentiometric titration of Pb(II) ions with EDTA. The electrode can be used to accurately monitor the Pb(II) pollution in environmental waters.     

Lead ion-selective electrodes based on polyphenylenediamine as unique solid ionophores

A novel membrane electrode for Pb(II) ion detection based on semi-conducting poly(m-phenylenediamine) microparticles as a unique solid ionophore was fabricated. The electrode exhibited significantly enhanced response towards Pb(II) over the concentration range from 3.16 × 10⁻⁶ to 0.0316 M at pH 3.0-5.0 with a low detection limit of 6.31 × 10⁻⁷ M, a high sensitivity displaying a near-Nernstian slope of 29.8 mV decade⁻¹ for Pb(II). The electrode showed a long lifetime of 5 months and a short response time of 14 s. A systematical investigation on the effect of anion excluder and various foreign ions on the selectivity of the electrode by a fixed interference method suggests that all other metal ions hardly ever interfere with the determination of Pb(II) except high concentration Hg(II). The electrode was successfully used as an indicator electrode in the potentiometric titration of Pb(II) with EDTA. Furthermore, the electrode has been used to satisfactorily analyze four types of real-world samples like spiked human urine, spiked tap water, and river water containing interfering ions like Na(I), Ca(II), Mg(II), Zn(II), Pd(II), Fe(III), K(I), Cu(II) and Hg(II) up to 8.04 × 10⁻⁴ M, demonstrating fast response, high selectivity, good recovery (96.6-121.4%), good repeatability (RSD 0.31-6.45%), and small relative error (5.0%).     

On the Adsorption and Reduction of the Herbicide Picloram on Mercury and Carbon Electrodes

At concentrations higher than 2?10^?4 M , and below pH 3, the cyclic voltammograms of picloram (=4‐amino‐3,5,6‐trichloropyridine‐2‐carboxylic acid) on Hg electrodes show two prepeak systems (named I and II attending to the proximity to the main reductions peak), which can be attributed to the weak adsorption of reactant and the strong adsorption of the product at the electrode surface. The system II is due to the uncharged form of picloram, and system I to the picloram protonated at the pyridine N‐atom. Small amounts of the surfactant Triton X‐100 (=α‐[4‐(1,1,3,3‐tetramethylbutyl)phenyl]‐ω‐hydroxypoly(oxyethane‐1,2‐diyl)) cause the disappearance of system I, the shift of system II, and also affect the intensities and widths of anodic and cathodic peaks but not the charge passed in each peak. Thus, the adsorption process responsible for the appearance of system I is inhibited by the presence of Triton; by contrast, the process corresponding to system II is only modified by the surfactant, becoming an electrochemical process occurring at the potentials corresponding to system II, which is more reversible than that observed in the absence of Triton. The addition of Triton permitted the analysis of the main reduction process. Convolution voltammetry of the main reduction peak is consistent with the loss of a Cl‐atom in equilibrium which occurs after a reversible electron transfer and is followed by the reductions of both species present in the equilibrium (Scheme 2). This is also the reduction mechanism on a glassy carbon electrode but the electron transfer on the carbon electrode increases with respect to the mercury electrodes; in addition, the loss of the Cl‐atom does not take place on the electrode surface. From the recording of differential capacity–potential curves, it was concluded that picloram is adsorbed on the carbon electrode; but this adsorption is too weak to induce the appearance of prepeak systems.     

Hydrogel-shelled biodegradable microspheres for sustained release of encapsulants

Biodegradable microparticles are promising for the sustained release of encapsulated lipophilic drugs. In particular, the microparticles with uniform size show excellent linearity of cumulated release over time with minimized initial burst. Here, we encapsulate the biodegradable microparticles with a hydrogel shell to improve the controllability over the sustained release and suspension stability. With a capillary microfluidic device, monodisperse oil-in-water-in-oil (O/W/O) double-emulsion droplets are produced to have a toluene solution of polylactic acid (PLA) in the core and sodium alginate and calcium-ethylenediaminetetraacetic acid (EDTA) complex in the shell, whereas the continuous oil phase contains acetic acid. As the toluene evaporates, PLA consolidates to form a microsphere in the core. At the same time, acetic acid diffuses from the continuous phase to the water layer, which causes the dissociation of the Ca-EDTA complex and the gelation of alginate. The hydrogel-shelled PLA microspheres are transferred from the oil to an aqueous solution of calcium chloride, which further tightens the gel shell. The resulting core-shell microspheres show sustained release of encapsulants for extended periods as the hydrogel shell serves as a diffusion barrier. Moreover, the hydrogel shells prevent interparticle agglomeration and adhesion to the solid walls, securing high suspension stability during the injection.     

Enhanced aggregation of alginate-coated iron oxide (hematite) nanoparticles in the presence of calcium, strontium, and barium cations

Early-stage aggregation kinetics studies of alginate-coated hematite nanoparticles in solutions containing alkaline-earth metal cations revealed enhanced aggregation rates in the presence of Ca2+, Sr2+, and Ba2+, but not with Mg2+. Transmission electron microscopy (TEM) imaging of the aggregates provided evidence that alginate gel formation was essential for enhanced aggregation to occur. Dynamic light scattering (DLS) aggregation results clearly indicated that a much lower concentration of Ba2+ compared to Ca2+ and Sr2+ was required to achieve a similar degree of enhanced aggregation in each system. To elucidate the relationship between the alginate's affinities for divalent cations and the enhanced aggregation of the alginate-coated hematite nanoparticles, atomic force microscopy (AFM) was employed to probe the interaction forces between alginate-coated hematite surfaces under the solution chemistries used for the aggregation study. Maximum adhesion forces, maximum pull-off distances, and the work of adhesion were used as indicators to gauge the alginate's affinity for the divalent cations and the resulting attractive interactions between alginate-coated hematite nanoparticles. The results showed that alginate had higher affinity for Ba2+ than either Sr2+ or Ca2+. This same trend was consistent with the cation concentrations required for comparable enhanced aggregation kinetics, suggesting that the rate of alginate gel formation controls the enhanced aggregation kinetics. An aggregation mechanism incorporating the gelation of alginate is proposed to explain the accelerated aggregate growth in the presence of Ca2+, Sr2+, and Ba2+.     

Composite microparticle drug delivery systems based on chitosan, alginate and pectin with improved pH-sensitive drug release property

Composite microparticle drug delivery systems based on chitosan, alginate and pectin with improved pH sensitivity were developed for oral delivery of protein drugs, using bovine serum albumin (BSA) as a model drug. The composite drug-loaded microparticles with a mean particle size less than 200 μm were prepared by a convenient shredding method. Since the microparticles were formed by tripolyphosphate cross-linking, electrostatic complexation by alginate and/or pectin, as well as ionotropic gelation with calcium ions, the microparticles exhibited an improved pH-sensitive drug release property. The in vitro drug release behaviors of the microparticles were studied in simulated gastric (pH 1.2 and pH 5.0), intestinal (pH 7.4) and colonic (pH 6.0 and pH 6.8 with enzyme) media. For the composite microparticles with suitable compositions, the releases of BSA at pH 1.2 and pH 5.0 could be effectively sustained, while the releases at pH 7.4, pH 6.8 and pH 6.0 increased significantly, especially in the presence of pectinase. These results clearly suggested that the microparticles had potential for site-specific protein drug delivery through oral administration.     

基于壳聚糖-溴化氰改性褐藻酸钠凝集作用的日本血吸虫安培免疫传感器

研制了一种基于壳聚糖和溴化氰改性褐藻酸钠凝集作用的日本血吸虫安培免疫传感器.褐藻酸钠-抗体复合物通过静电吸附作用被凝集到含石墨-石蜡-壳聚糖组分的电极表面,然后与抗原和酶标抗原进行竞争反应,以邻氨基酚(o-AP)为电子媒介,通过测定酶催化下双氧水对其氧化的电流大小来间接测定抗原的浓度.研究表明这种免疫传感器具有很低的非特异吸附性能,而且在经过简单的处理后可以重复使用,其重现性和灵敏度良好.传感器对日本血吸虫抗原的响应在0.64～40μg/mL之间呈线性关系.检测限为0.64μg/mL.将电极应用于兔血清中日本血吸虫抗原的测定,取得了满意结果.     

Gentle cell trapping and release on a microfluidic chip by in situ alginate hydrogel formation

Microfluidic devices are increasingly used to perform biological experiments on a single-cell basis. However, long-term stability of cell positions is still an issue. A novel biocompatible method for cell entrapment and release on a microchip is presented. It is based on the controlled formation of an alginate hydrogel by bringing two laminar flows of alginate and calcium ions in the range of 2 mM to 40 mM into contact. The resulting growth of a gel bar is used to enclose and immobilize yeast cells. Adding ethylenediaminetetraacetic acid (EDTA) to the alginate solution allows for control of the hydrogel growth, and by varying the ratio of Ca(2+) to EDTA concentrations gel growth or gel shrinkage can be induced at will. Trapped cells are released during shrinkage of the gel. The trapping efficiency for different cell speeds is investigated and the properties of gel growth are discussed using a diffusion model. Precise positioning of a single cell is demonstrated. The technique presented allows not only the reversible immobilization of cells under gentle conditions but also offers the potential of long-term cell cultures as shown by on-chip incubation of yeast cells. The procedure may provide a simple and fully biocompatible technique for a multitude of innovative experiments on cells in microsystems.     

Critical exponents and self-similarity for sol-gel transition in aqueous alginate systems induced by in situ release of calcium cations

The sol-gel transition in aqueous alginate systems induced by in situ released calcium cations was monitored with rheology methods. Four alginate samples with different molecular weights and M/G ratios were used over the concentration C(Alg) of 2 approximately 6 wt % with different mole ratios f of Ca2+ to the alginate repeat unit. The scaling for the zero shear viscosity eta(0) before the gel point and the equilibrium modulus Ge after the gel point was described as eta(0) approximately epsilon(-k) and Ge approximately epsilon(z), respectively, where the relative distance to the gel point f(gel) was epsilon = (/f-f(gel)/)/f(gel). The relaxation critical exponent n was determined with Winter's criterion, and the critical exponents k and z estimated respectively from independent measurements of eta(0) and Ge gave n from z/(k + z). Before the gel point, the storage and loss moduli G' and G' obtained at various epsilon can be superposed fairly well to form the master curve. The critical exponents n, k, and z were also evaluated from the shift factors and the structure self-similarity was found in the critical gel. The critical exponents evaluated with different methods agreed well with each other, suggesting two categories of the gelation as growth and cross-link. For the alginate with lower molecular weight, the critical exponents were almost independent of alginate concentration and close to the percolation prediction. For the alginate with higher molecular weight, the critical exponents, however, changed with alginate sample and concentration. The relative alginate concentration C(Alg)/C(Alg)* was found to serve as a criterion to divide these two transitions.