Magnetically separable and recyclable Fe3O4–polydopamine hybrid hollow microsphere for highly efficient peroxidase mimetic catalysts

An electrochemical immunosensor for sensitive and rapid detection of cystatin C based on Fe3O4/AuNPs-MWCNTs@PDA nanocomposite

Serum Cystatin C (CysC) is an impressive marker for early diagnosis of renal dysfunction. In this work, we established a novel electrochemical immunosensor based on Fe3O4/AuNPs-MWCNTs@PDA nanocomposite for the detection of CysC. The Fe3O4/AuNPs-MWCNTs@PDA nanozyme complex by polydopamine encapsulation can not only carry massive detection antibodies, but also bind the electroactive substance toluidine blue (TB) through electrostatic adsorption. By immobilizing AuNPs onto the electrode to bind the capture antibody (Ab1), we constructed a sandwich electrochemical immunosensor with low cost, high sensitivity, and repeatability. The detection range is 3.9-125.0 ng/mL with a significant linear relationship between the current peak difference (ip) and logarithm of the CysC concentration. Moreover, the detection limit of the immunosensor is 0.157 ng/mL. We have successfully utilized this novel immunosensor to detect CysC in human serum samples, and these results have implications for its potential use in clinical application.

Polydopamine Applications in Biomedicine and Environmental Science

This manuscript explores the multifaceted applications of polydopamine (PDA) across various scientific and industrial domains. It covers the chemical aspects of PDA and its potential in bone tissue engineering, implant enhancements, cancer treatment, and nanotechnology. The manuscript investigates PDA's roles in tissue engineering, cell culture technologies, surface modifications, drug delivery systems, and sensing techniques. Additionally, it highlights PDA's contributions to microfabrication, nanoengineering, and environmental applications. Through detailed testing and assessment, the study identifies limitations in PDA-related research, such as synthesis complexity, incomplete mechanistic understanding, and biocompatibility variability. It also proposes future research directions aimed at improving synthesis techniques, expanding biomedical applications, and enhancing sensing technologies to optimize PDA's efficacy and scalability.

Polydopamine on Copper-Doped Cerium Dioxide Nanosheets as Peroxidase Mimics for the Intelligent Detection of Cholesterol

The catalytic ability of nanozymes has become an enzymology hotspot in the field of application. Most nanozymes were characterized to simultaneously have oxidase-like and peroxidase-like activities, but the practical application often focuses on certain activity; other complex activities may cause interference. The peroxidase-like activity (POD-like activity) of nanozymes have been widely used in the colorimetric detection of H2O2 or substances producing H2O2 as an intermediate, such as the detection of small biological molecules with the oxidative reaction of a chromogenic reagent in the presence of POD-like nanozymes. In this work, we used polydopamine (PDA) as the surface coating of Cu-CeO2 nanosheets (PDA@ Cu-CeO2), which enhanced peroxidase-like activity while inhibiting their oxidase-like activity, providing a feasible method for the sensitive determination of cholesterol by integrating visual colorimetric detection and a smartphone application as a readout. The absorbance intensity and RGB values displayed a linear range on cholesterol from 0.05 to 1.2 mM with the LOD (limit of detection) of 42.7 and 99.4 μM. In addition, the method is expected to apply in detecting cholesterol in human serum with acceptable accuracy.

Polydopamine nanomaterials and their potential applications in the treatment of autoimmune diseases

The conventional treatment methods used for the management of autoimmune diseases (ADs) have limited efficacy and also exhibit significant side effects. Thus, identification of novel strategies to improve the efficacy and safety of ADs treatment is urgently required. Overactivated immune response and oxidative stress are common characteristics associated with ADs. Polydopamine (PDA), as a polymer material with good antioxidant and photothermal conversion properties, has displayed useful application potential against ADs. In addition, PDA possesses good biosafety, simple preparation, and easy functionalization, which is conducive for the pharmacological development of PDA nanomaterials with clinical transformation prospects. Here, we have first reviewed the preparation of PDA, the different functional integration strategies of PDA-based biomaterials, and their potential applications in ADs. Next, the mechanism of action of PDA in ADs has been elaborated in detail. Finally, the application opportunities and challenges linked with PDA nanomaterials for ADs treatment are discussed. This review is contributed to design reasonable and effective PDA nanomaterials for the diagnosis and treatment of ADs.

Specific sensing of resorcin based on the hierarchical porous nanoprobes constructed by cuttlefish-derived biomaterials through differential pulse voltammetry

The specific detection of resorcin from its isomers is a current research hotspot. Thus in our work, a ternary hierarchical porous nanoprobe has been constructed based on the combination of cuttlefish ink and bimetallic Au@Ag nanoclusters for the specific sensing of resorcin. Briefly, through electrostatic interaction, Au@Ag core-shell nanoclusters are immobilized on the surface of polydopamine extracted from cuttlefish, which is turned into nitrogen-doped porous carbon functionalized by bimetallic Au@Ag by topological transformation subsequently. Afterward, an electrochemical sensor is fabricated based on the nanoprobes for specifically determining resorcin in solution by differential pulse voltammetry, and the linear detection ranges of the sensor are 1-100 μM and 1.2-4 mM while the detection limit reaches 0.06 μM. Meanwhile, the sensing mechanism of resorcin by the pre-fabricated sensor is detailedly studied by density functional theory to obtain a clear electrochemical process. Besides, the selectivity, stability, plus reproducibility of the pre-fabricated sensor have been also tested, and the determinations for resorcin in real environmental water samples have also been performed with good recoveries, revealing the auspicious application potential in the environmental monitoring.

Fabrication, functionalization and advanced applications of magnetic hollow materials in confined catalysis and environmental remediation

Magnetic hollow-structured functional hybrid materials with unique architectures and preeminent properties have always been an area of extensive research. They represent a subtle collaboration of hollow architecture, mesoporous nanostructure and magnetic character. Owing to the merits of a large void space, low density, high specific surface area, well-defined active sites and facile magnetic recovery, these materials present promising application projections in numerous fields, such as drug delivery, adsorption, storage, catalysis and many others. In this review, recent progress in the design, synthesis, functionalization and applications of magnetic hollow-meso/nanostructured materials are discussed. The first part of the review has been dedicated to the preparation and functionalization of the materials. The synthetic protocols have been broadly classified into template-assisted and template-free methods and major trends in their synthesis have been elaborated in detail. Furthermore, the benefits and drawbacks of each method are compared. The later part summarizes the application aspects of confined catalysis in organic transformations and environmental remediation such as degradation of organic pollutants, dyes and antibiotics and adsorption of heavy metal ions. Finally, an outlook of future directions in this research field is highlighted.

Magnetic Nanoparticle Composites: Synergistic Effects and Applications

Composite materials are made from two or more constituent materials with distinct physical or chemical properties that, when combined, produce a material with characteristics which are at least to some degree different from its individual components. Nanocomposite materials are composed of different materials of which at least one has nanoscale dimensions. Common types of nanocomposites consist of a combination of two different elements, with a nanoparticle that is linked to, or surrounded by, another organic or inorganic material, for example in a core-shell or heterostructure configuration. A general family of nanoparticle composites concerns the coating of a nanoscale material by a polymer, SiO2 or carbon. Other materials, such as graphene or graphene oxide (GO), are used as supports forming composites when nanoscale materials are deposited onto them. In this Review we focus on magnetic nanocomposites, describing their synthetic methods, physical properties and applications. Several types of nanocomposites are presented, according to their composition, morphology or surface functionalization. Their applications are largely due to the synergistic effects that appear thanks to the co-existence of two different materials and to their interface, resulting in properties often better than those of their single-phase components. Applications discussed concern magnetically separable catalysts, water treatment, diagnostics-sensing and biomedicine.

Au-Fe3O4 decorated polydopamine hollow nanoparticles as high performance catalysts with magnetic responsive properties

We demonstrated a simple approach for fabricating Au-Fe₃O₄/PDA hollow nanoparticles as high-performance catalysts for water purification. The polydopamine (PDA) shell was in situ formed on the silica surface from self-polymerization, which acts as a medium support for coupling with metal ions (for Fe₃O₄ nanoparticle deposition) as well as a reducing agent and stabilizer for Au nanoparticle reduction and deposition. A step of simultaneous Fe₃O₄ nanoparticle deposition and silica core removal under alkaline conditions is first introduced in this study. This process significantly simplifies previous strategies which typically require the use of poisonous agents such as hydrogen fluoride or additional complicated post-treatment steps. Under optimized conditions, the Au-Fe₃O₄/PDA hollow nanoparticles show a high saturation magnetization of 18.8 emu g^-1 and an excellent catalytic performance for the rapid reduction of p-nitrophenol with the reaction kinetic constant of 0.34 min^-1. This catalyst can be easily recovered using a permanent magnet and recycled eight times with a high catalytic cycle stability. The strategy presented in this work provides a facile and versatile approach towards designing complicated Au-Fe₃O₄/PDA hollow nanostructures, which might have great potential for many applications within biological, energy, and environmental technologies.

Well-water-dispersed N-trimethyl chitosan/Fe3O4 hybrid nanoparticles as peroxidase mimetics for quick and effective elimination of bacteria

Fe₃O₄ nanoparticles, used as peroxidase mimetics, exhibit splendid future in the biomedical field. However, the functionalization on Fe₃O₄ nanoparticles always goes with the loss of superparamagnetism and decrease in peroxidase-activity. Here, we synthesized green polyethylene glycol (PEG)-functionalized magnetic/N-trimethyl chitosan (CS) hybrid nanoparticles (Fe₃O₄@PAA/TMC/PEG NPs) with improved water dispersibility, superparamagnetism, high saturation magnetization and well peroxidase-like activity. The functionalized coating was divided in two steps, one involved a cross-linked PEG/PAA/CS middle layer to protect the nanocrystal Fe₃O₄ from oxidization, the other was a hydrophilic PEG/TMC outer layer improving the water dispersion, biocompatibility, as well as supplying positive quaternary ammonium groups for a potential increase of cell binding efficiency. The structure, composition and morphology of Fe₃O₄@PAA/TMC/PEG NPs were characterized by TEM, FT-IR spectroscopy, DLS, zeta potential measurement, respectively. Thermal performance was characterized by TGA, and the peroxidase-like mimics activity was tested by TMB·2HCl colour development experiments. The magnetic property of the as-prepared hybrid nanoparticles was first confirmed by VSM, and then proved by the bacterial pathogens adsorption, especially at ultralow pathogen concentration. Particularly, with an external magnet, the Fe₃O₄@PAA/TMC/PEG NPs, combined cationic quaternary ammonium groups and peroxidise-mimetic catalytic activity, were tested for antibacterial effect by plating method.

Polydopamine functionalized hydrogel beads as magnetically separable antibacterial materials

In the present study, magnetically separable hydrogel beads of ionically cross-linked alginate were functionalized with polydopamine (PDA). The rationale behind this was to enhance the structural stability and antibacterial profile of PDA/Alg/Fe₃O₄ beads (K3). Incorporation of superparamagnetic magnetite (Fe₃O₄) nanoparticles endowed the hydrogel beads with magnetism. X-ray diffraction (XRD) analysis revealed the successful formation of pure Alg/Fe₃O₄ nanoparticles having an inverse spinel structure. Vibrating sample magnetometry (VSM) confirmed their superparamagnetic behaviour with M_s values of 36.18 and 30.46 emu g⁻¹ at 5 and 300 K, respectively. High resolution-transmission electron microscopy (HR-TEM) images showed alginate capping and the size of the Alg/Fe₃O₄ nanoparticles (∼8 nm). The successful deposition of PDA granules on the K3 bead surface was verified by field emission-scanning electron microscopy (FE-SEM). The PDA functionalization was further justified by VSM, XRD and Fourier-transform infrared spectroscopy (FT-IR). During swelling experiments, K3 beads displayed appreciable structural stability compared to bare/non-functionalized beads. Wettability studies revealed K3 beads to be hydrophilic with a contact angle of ∼55°. Rheological parameters including storage modulus (G′) and shear viscosity of K3 increased upon PDA functionalization. During antibacterial tests, K3 strongly inhibited E. coli, S. typhi, S. aureus and L. monocytogenes in a concentration and time dependent manner. Fluorescence staining experiments showed that K3 could greatly alter the bacterial membrane integrity. Reusability experiments with K3 beads substantiated their effective broad-spectrum antibacterial performance for three consecutive cycles.

Surface functionalization with polydopamine augments the structural stability and antibacterial profile of magnetic hydrogel beads.

Recent progress in the biomedical applications of polydopamine nanostructures

Polydopamine is a dark brown-black insoluble biopolymer produced by autoxidation of dopamine. Although its structure and polymerization mechanism have not been fully understood, there has been a rapid growth in the synthesis and applications of polydopamine nanostructures in biomedical fields such as drug delivery, photothermal therapy, bone and tissue engineering, and cell adhesion and patterning, as well as antimicrobial applications. This article is dedicated to reviewing some of the recent polydopamine developments in these biomedical fields. Firstly, the polymerization mechanism is introduced with a discussion of the factors that influence the polymerization process. The discussion is followed by the introduction of various forms of polydopamine nanostructures and their recent applications in biomedical fields, especially in drug delivery. Finally, the review is summarized followed by brief comments on the future prospects of polydopamine.

Enhancing electrical energy storage capability of dielectric polymer nanocomposites via the room temperature Coulomb blockade effect of ultra-small platinum nanoparticles

Introducing a high dielectric constant (high-k) nanofiller into a dielectric polymer is the most common way to achieve flexible nanocomposites for electrostatic energy storage devices. However, the significant decrease of breakdown strength and large increase of dielectric loss has long been known as the bottleneck restricting the enhancement of practical energy storage capability of the nanocomposites. In this study, by introducing ultra-small platinum (<2 nm) nanoparticles, high-k polymer nanocomposites with high breakdown strength and low dielectric loss were prepared successfully. Core-shell structured polydopamine@BaTiO₃ (PDA@BT) and core-satellite ultra-small platinum decorated PDA@BT (Pt@PDA@BT) were used as nanofillers. Compared with PDA@BT nanocomposites, the maximum discharged energy density of the Pt@PDA@BT nanocomposites is increased by nearly 70% because of the improved energy storage efficiency. This research provides a simple, promising and unique way to enhance energy storage capability of high-k polymer nanocomposites.

Distinguished Cr(VI) capture with rapid and superior capability using polydopamine microsphere: Behavior and mechanism

Toxic heavy metal containing Cr(VI) species is a serious threat for ecological environment and human beings. In this work, a new mussel-inspired polydopamine microsphere (PDA-sphere) is prepared through in situ oxidative polymerization at air condition with controllable sizes. The adsorption of Cr(VI) ions onto PDA-sphere is highly pH dependent with the optimal pH ranging from 2.5 to 3.8. A rapid Cr(VI) removal can approach in 8min for equilibrium. More importantly, the prepared materials exhibit a remarkable sorption selectivity, coexisting SO₄^2-, NO₃^- and Cl^- ions at high levels; The applicability model further proves its effective performances with treated capacity of 42,000kg/kg sorbent, and the effluent can be reduced from 2000ppb to below 50ppb, which meets the drinking water criterions recommended by WHO. 1kg sorbent can also purify approximately 100t Cr(VI) contaminated wastewaters basing on the wastewater discharges of China. Such capacity for application ranks the top level for Cr(VI) removal. Additionally, the exhausted materials can be well regenerated by binary alkaline and salts mixtures. Such efficient adsorption can be ascribed to the well-dispersed morphology as well as the strong affinity between Cr(VI) and catechol or amine groups by XPS investigation. All the results suggest that polydopamine microspheres may be ideal materials for Cr(VI) treatment in waters.

Enhanced peroxidase-like activity of porphyrin functionalized ZnFe2O4 hollow nanospheres for rapid detection of H2O2 and glucose

Using a simple one-pot solvothermal method, binary metal oxide, magnetic and hollow ZnFe₂O₄ nanospheres functionalized with 5,10,15,20-tetrakis(4-carboxylpheyl)-porphyrin (Por–ZnFe₂O₄ HSs) were prepared and subsequently applied as a substitute for natural peroxidase.

Co-delivery of docetaxel and bortezomib based on a targeting nanoplatform for enhancing cancer chemotherapy effects

Using facile polydopamine (PDA)-based surface modification and a pH-sensitive catechol-boronate binding mechanism, a novel drug delivery system was designed for the treatment of breast cancer. The system was able to achieve the following goals: active targeting, pH responsiveness, in vivo blood circulation for a prolonged period of time, and dual drug loading. After coating with PDA, the docetaxel (DTX)-loaded star-shaped copolymer cholic acid-poly(lactide-co-glycolide) nanoparticles (CA-PLGA@PDA/NPs) were functionalized with amino-poly(ethylene glycol)-folic acid (NH2-PEG-FA) and bortezomib (BTZ) to form the targeting composition, DTX-loaded CA-PLGA@PDA-PEG-FA + BTZ/NPs. The novel NPs exhibited similar drug release characteristics compared to unfunctionalized CA-PLGA/NPs. Meanwhile, the incorporated NH2-PEG-FA contributed to active targeting which was illustrated by cellular uptake experiments and biodistribution studies. Moreover, the pH responsive binding between BTZ and PDA was demonstrated to be effective to release BTZ at the tumor acidic environment for synergistic action with DTX. Both in vitro cytotoxicity and in vivo antitumor studies demonstrated that the novel nanoplatform exhibited the most suitable therapeutic effects. Taken together, the versatile PDA modified DTX-loaded CA-PLGA@PDA-PEG-FA + BTZ/NPs offered a promising chemotherapeutic strategy for enhancing breast cancer treatment.

Iron Oxide Nanozyme: A Multifunctional Enzyme Mimetic for Biomedical Applications

Iron oxide nanoparticles have been widely used in many important fields due to their excellent nanoscale physical properties, such as magnetism/superparamagnetism. They are usually assumed to be biologically inert in biomedical applications. However, iron oxide nanoparticles were recently found to also possess intrinsic enzyme-like activities, and are now regarded as novel enzyme mimetics. A special term, "Nanozyme", has thus been coined to highlight the intrinsic enzymatic properties of such nanomaterials. Since then, iron oxide nanoparticles have been used as nanozymes to facilitate biomedical applications. In this review, we will introduce the enzymatic features of iron oxide nanozyme (IONzyme), and summarize its novel applications in biomedicine.

Preparation of Magnetically Recyclable Yolk/Shell Fex Oy /PdPt@CeO2 Nanoreactors with Enhanced Catalytic Activity

Noble metal nanoparticles (NPs) have recently received considerable attention from researchers working in the field of catalysis. However, the development of new methods allowing these materials to reach their maximum catalytic properties remains challenging. Nanoreactors could lead to dramatic improvements in activity with the help of the intrinsic confinement effect. In this study, we designed a series of yolk/shell Fe_x O_y /PdPt@CeO₂ composites, where the Fe_x O_y NPs acted as a movable core, allowing for the uniform distribution of the PdPt alloys on the inner surface of the CeO₂ shell. The high porosity and existence of hollow voids in the CeO₂ shell allowed these Fe_x O_y /PdPt@CeO₂ composites to be used as nanoreactors in catalytic reactions. As well this confinement effect, we identified two structural features that led to enhanced catalytic activity, including (i) the replacement of monometallic NPs with a bimetallic PdPt alloy and (ii) the replacement of a chemically inert support with a reactive CeO₂ shell. The resulting nanoassembled catalysts displayed higher activities toward the catalytic reduction of dyes than the reference samples. Moreover, these catalysts were readily recovered and reused because of the magnetic Fe_x O_y core.

Fabrication of Stretchable Nanocomposites with High Energy Density and Low Loss from Cross-Linked PVDF Filled with Poly(dopamine) Encapsulated BaTiO3

In this report, a simple solution-cast method was employed to prepare poly(dopamine) (PDA) encapsulated BaTiO₃ (BT) nanoparticle (PDA@BT) filled composites using PVDF matrix cross-linked by the free radical initiator. The effects of both the particle encapsulation and matrix cross-linking on the mechanical and dielectric properties of the composites were carefully investigated. The results suggested that the introduction of BT particles improved permittivity of the composites to ∼30 at 100 Hz when particle contents of only 7 wt % were utilized. This was attributed to the enhanced polarization, which was induced by high permittivity ceramic particles. Compared to bare BT, PDA@BT particles could be dispersed more homogeneously in the matrix, and the catechol groups of PDA layer might form chelation with free ions present in the matrix. The latter might depress the ion conduction loss in the composites. Other results revealed that the formation of hydrogen-bonding between the PDA layer and the polymer, especially the chemical cross-linking across the matrix, resulted in increased Young' modulus by ∼25%, improved breakdown strength by ∼40%, and declined conductivity by nearly 1 order of magnitude when compared to BT filled composites. The composite films filled with PDA@BTs indicated greater energy storage capacities by nearly 190% when compared to the pristine matrix. More importantly, the excellent mechanical performance allowed the composite films to adopt uni- or biaxially stretching, a crucial feature required for the realization of high breakdown strength. This work provided a facile strategy for fabrication of flexible and stretchable dielectric composites with depressed dielectric loss and enhanced energy storage capacity at low filler loadings (<10 wt %).

Environmental implications and applications of engineered nanoscale magnetite and its hybrid nanocomposites: A review of recent literature

This review focuses on environmental implications and applications of engineered magnetite (Fe3O4) nanoparticles (MNPs) as a single phase or a component of a hybrid nanocomposite that exhibits superparamagnetism and high surface area. MNPs are synthesized via co-precipitation, thermal decomposition and combustion, hydrothermal process, emulsion, microbial process, and green approaches. Aggregation/sedimentation and transport of MNPs depend on surface charge of MNPs and geochemical parameters such as pH, ionic strength, and organic matter. MNPs generally have low toxicity to humans and ecosystem. MNPs are used for constructing chemical/biosensors and for catalyzing a variety of chemical reactions. MNPs are used for air cleanup and carbon sequestration. MNP nanocomposites are designed as antimicrobial agents for water disinfection and flocculants for water treatment. Conjugated MNPs are widely used for adsorptive/separative removal of organics, dyes, oil, arsenic, phosphate, molybdate, fluoride, selenium, Cr(VI), heavy metal cations, radionuclides, and rare earth elements. MNPs can degrade organic/inorganic contaminants via chemical reduction or catalyze chemical oxidation in water, sediment, and soil. Future studies should further explore mechanisms of MNP interactions with other nanomaterials and contaminants, economic and green approaches of MNP synthesis, and field scale demonstration of MNP utilization.

Controlled synthesis of water-dispersible and superparamagnetic Fe3O4 nanomaterials by a microwave-assisted solvothermal method: from nanocrystals to nanoclusters

Highly tunable Fe₃O₄ nanocrystals and nanoclusters with water-dispersible and superparamagnetic properties were successfully synthesized by a facile and effective microwave-assisted solvothermal method.

Fe3O4@P(DVB/MAA)/Pd composite microspheres: preparation and catalytic degradation performance

Fe₃O₄@P(DVB/MAA)/Pd composite microspheres were synthesized with a combination of coating and loading processes using Fe₃O₄ nanoparticles as a core.