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•LDH-biopolymer interactions must be understood to design hybrid materials.•Biopolymer adsorption changes the surface charge and aggregation properties.•Colloidal stability of the ...composites must be tuned to avoid particle aggregation.•Biopolymers proved to stabilize delivery particle systems during medical uses.•Quantitative dispersion studies on LDH-biopolymer systems are still needed.
Layered double hydroxides (LDHs) are appealing nanomaterials for (bio)medical applications and their potential is threefold. One can gain advantage of the structure of LDH frame (i.e., layered morphology), anion exchanging property towards drugs with acidic character and tendency for facile surface modification with biopolymers. This review focuses on the third aspect, as it is necessary to evaluate the advantages of polymer adsorption on LDH surfaces. Beside the short discussion on fundamental and structural features of LDHs, LDH-biopolymer interactions will be classified in terms of the effect on the colloidal stability of the dispersions. Thereafter, an overview on the biocompatibility and biomedical applications of LDH-biopolymer composite materials will be given. Finally, the advances made in the field will be summarized and future research directions will be suggested.
The effect of papain adsorption on the surface charge properties and aggregation mechanism of sulfate-functionalized polystyrene latex particles was studied. The positively charged enzyme possessed a ...high affinity to the oppositely charged particles, giving rise to charge neutralization and charge reversal at appropriate papain concentrations. The tendency in the particle aggregation rates at different enzyme doses revealed that the colloidal stability of the samples is governed by interparticle forces of electrostatic origin. The aggregation mechanism was qualitatively described within the classical DLVO theory, and unstable dispersions were detected near the charge neutralization point, while particle aggregation was not observed at low and elevated papain concentrations. The relatively high dispersion stability of the bare latex particles was maintained upon the formation of an enzyme layer on the surface, and the obtained latex–papain composite showed notable resistance against salt-induced aggregation. Remarkable hydrolytic and antioxidant activities of the immobilized enzyme were observed in probe reactions; therefore, the obtained hybrid can be considered as a multifunctional biocatalytic system with great promise in applications in industrial manufacturing processes.
Colloidal stability was investigated in two types of particle systems, namely, with bare (h-HNT) and polyimidazolium-functionalized (h-HNT–IP-2) alkali-treated halloysite nanotubes in solutions of ...metal salts and ionic liquids (ILs). The valence of the metal ions and the number of carbon atoms in the hydrocarbon chain of the IL cations (1-methylimidazolium (MIM+), 1-ethyl-3-methylimidazolium (EMIM+), 1-butyl-3-methylimidazolium (BMIM+), and 1-hexyl-3-methylimidazolium (HMIM+)) were altered in the measurements. For the bare h-HNT with a negative surface charge, multivalent counterions destabilized the dispersions at low values of critical coagulation concentration (CCC) in line with the Schulze–Hardy rule. In the presence of ILs, significant adsorption of HMIM+ took place on the h-HNT surface, leading to charge neutralization and overcharging at appropriate concentrations. A weaker affinity was observed for MIM+, EMIM+, and BMIM+, while they adsorbed on the particles to different extents. The order HMIM+ < BMIM+ < EMIM+ < MIM+ was obtained for the CCCs of h-HNT, indicating that HMIM+ was the most effective in the destabilization of the colloids. For h-HNT–IP-2 with a positive surface charge, no specific interaction was observed between the salt and the IL constituent cations and the particles, i.e., the determined charge and aggregation parameters were the same within experimental error, irrespective of the type of co-ions. These results clearly indicate the relevance of ion adsorption in the colloidal stability of the nanotubes and thus provide useful information for further design of processable h-HNT dispersions.
Antioxidant colloids were developed via controlled heteroaggregation of cerium oxide nanoparticles (CeO2 NPs) and sulfate-functionalized polystyrene latex (SL) beads. Positively charged CeO2 NPs were ...directly immobilized onto SL particles of opposite surface charge via electrostatic attraction (SL/Ce composite), while negatively charged CeO2 NPs were initially functionalized with poly(diallyldimethylammonium chloride) (PDADMAC) polyelectrolyte and then, aggregated with the SL particles (SPCe composite). The PDADMAC served to induce a charge reversal on CeO2 NPs, while the SL support prevented nanoparticle aggregation under conditions, where the dispersions of bare CeO2 NPs were unstable. Both SL/Ce and SPCe showed enhanced radical scavenging activity compared to bare CeO2 NPs and were found to mimic peroxidase enzymes. The results demonstrate that SL beads are suitable supports to formulate CeO2 particles and to achieve remarkable dispersion storage stability. The PDADMAC functionalization and immobilization of CeO2 NPs neither compromised the peroxidase-like activity nor the radical scavenging potential. The obtained SL/Ce and SPCe artificial enzymes are foreseen to be excellent antioxidant agents in various applications in the biomedical, food, and cosmetic industries.
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•CeO2 NPs were immobilized onto sulfate latex particles at two pH regimes.•Direct immobilization was achieved under acidic conditions.•Surface modification of CeO2 was required for immobilization at alkaline pH.•High stability of the composites was achieved by optimization of the mass ratio.•The formulated composites exhibited excellent antioxidant enzyme-like activity.
•Inorganic-organic composite thin film was fabricated by spray coating.•Photodetecting properties indicates an n-p heterojunction formation.•The film shows linear sensitivity and rapid response for ...ethanol at room temperature.
Hybrid thin film sensors based on semiconductor oxides and carbon nanostructures are promising materials to improve the sensing, thermomechanical and optical properties. In this study, a thin film based on a composite from ZnO nanoparticles, milled multiwalled carbon nanotubes, and conducting polymer was fabricated. The layer was spray-coated to the surface of amorphous polyethylene terephthalate substrate. The hybrid layer and components have been systematically characterized by transmission and scanning electron microscopy, dynamic light scattering and the optical absorption spectrum was observed by ultraviolet-visible spectroscopy. The change in glass transition temperature was measured by dynamic mechanical analysis. Gas sensing tests reveal that the ZnO/multiwalled carbon nanotube/ poly(3,4-ethylenedioxythiophene): polystyrene sulfonate film on amorphous polyethylene terephthalate has remarkably enhanced performance compared to the same layer on indium tin oxide /polyethylene terephthalate. It could detect ethanol vapor in a wide concentration range with good response, fast recovery, and repeatability at room temperature. The layer was also tested as an ultraviolet photodetector, showing a promising signal. These features indicate the composite usability in further sensor applications.
Radical scavenging activity of extracts obtained from 16 plants harvested in South Hungary was assessed and compared to the activity of ascorbic acid standard. During extraction, a novel technique ...involving an ethanolic treatment at ambient temperature was used for advanced active component release. Although the procedure is time consuming, it serves as an efficient and harmless route to extract valuable antioxidant compounds from their natural sources. The as-prepared extracts consist of two phases (except Allium sativum), a clear solution and a thick suspension containing solid plant parts that separates in about 2 h. The samples were analysed by the antioxidant assay based on the scavenging of 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radicals. For most of the species, the solid phase retained considerable amount of available antioxidant agents, while the solution parts showed significant radical scavenging activity. The main exceptions were Nigella sativa, Hippophae rhamnoides and Linum usitatissimum, where the solid parts were less active. Overall, the extracts possessed remarkable antioxidant activity that were compared to published literature data and were found to be superior.
Natural product chemistry; Physical chemistry; Food science, Herbal extracts; Antioxidant activity; Plant processing; DPPH assay; Radical scavenge
The detection and quantification of antioxidant molecules is an important task in food science, the fine chemical industry and healthcare. Antioxidants help in preventing the deterioration of ...nutrition and healthcare products, while eliminating over-the-limit exogenic reactive species, which may lead to illnesses. In our contribution, an inexpensive and rapid method to determine the concentration of various molecular antioxidants was developed. The principle of the analysis relies on the cupric ion reducing antioxidant capacity (CuPRAC) method, which is based on the color-changing reduction of chelated Cu
ions. This complex was successfully immobilized on an alginate-functionalized layered double hydroxide (dLDH) nanosheet
electrostatic interactions. The synthesis conditions of alginate (NaAlg) and the cupric complex were optimized, and the optimized composite was fabricated on cellulose paper to obtain a sensing platform. The paper-based sensor was superior to the ones prepared without the dLDH support, as the limit of detection (LOD) values decreased, and the linearity ranges broadened. The results offer a single-point measurement to evaluate the antioxidant efficiency in a cuvette-based method. The superior ability of the sensor was assigned to the presence of solid dLDH particles, as they offer adsorption sites for the dissolved antioxidant molecules, which contributes significantly to the decrease of the diffusion limitation during the detection process.
Biocompatible Cu(II)-doped layered double hydroxide (CMA) nanoparticles were developed to combat reactive oxygen species. The 2-dimensional nanozymes showed both superoxide dismutase- and ...catalase-like activities in chemical assays, while proving as efficient antioxidants in the reduction of intracellular oxidative stress. The results indicate the great promise of CMA in antioxidant therapies.
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