Iron-based magnetic nanomaterials in environmental and energy applications: a short review

Advancements in enzyme immobilization on magnetic nanomaterials: toward sustainable industrial applications

Enzymes are widely used in biofuels, food, and pharmaceuticals. The immobilization of enzymes on solid supports, particularly magnetic nanomaterials, enhances their stability and catalytic activity. Magnetic nanomaterials are chosen for their versatility, large surface area, and superparamagnetic properties, which allow for easy separation and reuse in industrial processes. Researchers focus on the synthesis of appropriate nanomaterials tailored for specific purposes. Immobilization protocols are predefined and adapted to both enzymes and support requirements for optimal efficiency. This review provides a detailed exploration of the application of magnetic nanomaterials in enzyme immobilization protocols. It covers methods, challenges, advantages, and future perspectives, starting with general aspects of magnetic nanomaterials, their synthesis, and applications as matrices for solid enzyme stabilization. The discussion then delves into existing enzymatic immobilization methods on magnetic nanomaterials, highlighting advantages, challenges, and potential applications. Further sections explore the industrial use of various enzymes immobilized on these materials, the development of enzyme-based bioreactors, and prospects for these biocatalysts. In summary, this review provides a concise comparison of the use of magnetic nanomaterials for enzyme stabilization, highlighting potential industrial applications and contributing to manufacturing optimization.

Biodegradation of pyrene by bacterial consortia: Impact of natural surfactants and iron oxide nanoparticles

Polycyclic aromatic hydrocarbons (PAHs) are potentially hazardous compounds that could cause a severe impact on many ecosystems. They are very challenging to remove using conventional methods due to their hydrophobic nature. However, this issue can be resolved by utilizing surface-active molecules to increase their bioavailability. In this study, pyrene was chosen as the PAH compound to explore its degradability by the effect of individual bacterial strains (Pseudomonas stutzeri NA3 and Acinetobacter baumannii MN3) and mixed consortia (MC) along with natural surfactant derived from Sapindus mukorossi and iron oxide nanoparticles (NPs). Additionally, fatty acids esters, dipeptides, and sugar derivative groups were identified as potent bioactive components of natural surfactants. Various techniques, such as XRD, VSM, TEM, and FE-SEM with EDX, were utilized to characterize the pristine and Fenton-treated iron oxide NPs. The analytical results confirmed that the Fe3O4 crystal phase and spherical-shaped NPs exhibited excellent magnetic properties. The impact of natural surfactants and iron oxide NPs has significantly contributed to the biodegradation process, resulting in a prominent decrease in chemical oxygen demand (COD) levels. Gas chromatography-mass spectrometry (GC-MS) analysis showed that biodegradation systems produced primary hydrocarbon intermediates, which underwent oxidative degradation through Fenton treatment. Interestingly, synthesized iron oxide NPs effectively produced hydroxyl radical (•OH) during the Fenton reaction, which was confirmed by electron paramagnetic resonance (EPR) spectra, and the pristine iron oxide NPs underwent a material transformation observed. The study demonstrated an integrated approach for biodegradation and the Fenton reaction process to enhance the pyrene degradation efficiency (90%) compared to other systems. Using natural surfactants and iron oxide NPs in aquatic environments serves as a crucial platform at the interface of microorganisms and contaminated oil products. This interaction offers a promising solution for PAHs bioremediation.

Emerging iron-based mesoporous materials for adsorptive removal of pollutants: Mechanism, optimization, challenges, and future perspective

Iron-based materials (IBMs) have shown promise as adsorbents due to their unique physicochemical properties. This review provides an overview of the different types of IBMs, their synthesis methods, and their properties. Results found in the adsorption of emerging contaminants to a wide range of IBMs are discussed. The IBMs used were evaluated in terms of their maximum uptake capacity, with special consideration given to environmental conditions such as contact time, solution pH, initial pollutant concentration, etc. The adsorption mechanisms of pollutants are discussed taking into account the results of kinetic, isotherm, thermodynamic studies, surface complexation modelling (SCM), and available spectroscopic data. A current overview of molecular modeling and simulation studies related to density functional theory (DFT), surface response methodology (RSM), and artificial neural network (ANN) is presented. In addition, the reusability and suitability of IBMs in real wastewater treatment is shown. The review concludes with the strengths and weaknesses of current research and suggests ideas for future research that will improve our ability to remove contaminants from real wastewater streams.

Recent progress in MoS2 nanostructures for biomedical applications: Experimental and computational approach

In the category of 2D materials, MoS2 a transition metal dichalcogenide, is a novel and intriguing class of materials with interesting physicochemical properties, explored in applications ranging from cutting-edge optoelectronic to the frontiers of biomedical and biotechnology. MoS2 nanostructures an alternative to heavy toxic metals exhibit biocompatibility, low toxicity and high stability, and high binding affinity to biomolecules. MoS2 nanostructures provide a lot of opportunities for the advancement of novel biosensing, nanodrug delivery system, electrochemical detection, bioimaging, and photothermal therapy. Much efforts have been made in recent years to improve their physiochemical properties by developing a better synthesis approach, surface functionalization, and biocompatibility for their safe use in the advancement of biomedical applications. The understanding of parameters involved during the development of nanostructures for their safe utilization in biomedical applications has been discussed. Computational studies are included in this article to understand better the properties of MoS2 and the mechanism involved in their interaction with biomolecules. As a result, we anticipate that this combined experimental and computational studies of MoS2 will inspire the development of nanostructures with smart drug delivery systems, and add value to the understanding of two-dimensional smart nano-carriers.

Simultaneous estimation of magnetic moment and Brownian relaxation time distributions of magnetic nanoparticles based on magnetic particle spectroscopy for biosensing application

Magnetic nanoparticles (MNPs) exhibit unique physicochemical characteristics owing to their comparable dimensions with important biological substances, high surface-to-volume ratios, size-dependent magnetic properties, and temperature sensitivity. In this study, we present a novel method for simultaneously estimating the magnetic moment and Brownian relaxation time distribution of MNPs based on AC magnetization harmonics. We provide a detailed description of the theoretical framework and experimental procedures. The dynamics of MNP magnetization are described using the Fokker-Planck equation, and a matrix equation is established to connect the magnetic moment, Brownian relaxation time, and magnetization harmonics. By employing a non-negative linear least squares algorithm with constraints, the magnetic moment and Brownian relaxation time distributions are inversed, which are then converted into the distributions of core sizes and hydrodynamic sizes. Finally, the estimated core size distribution reconstructed from M-H curves is consistent with the hydrodynamic size distribution measured by dynamic light scattering. This method is particularly useful for facilitating quantitative magnetic immunoassays.

Designing novel perlite-Fe3O4@SiO2@8-HQ-5-SA as a promising magnetic nanoadsorbent for competitive adsorption of multicomponent VOCs

Volatile organic compounds (VOCs), which emerge as multicomponent pollutants through many industrial processes, pose a serious threat to human health and the eco-environment due to their volatility, toxicity and dispersion. Hence, the study of competitive adsorption of multicomponent VOCs is of practical and scientific importance. Herein, the perlite-supported Fe3O4@SiO2@8-hydroxyquinoline-5-sulfonic acid (perlite-Fe3O4@SiO2@8-HQ-5-SA) was designed as a novel magnetic nanoadsorbent by a simple strategy and employed for the competitive adsorption of multicomponent toluene, ethylbenzene and xylene in the vapor-phase targeted as VOCs. The successfully prepared perlite-Fe3O4@SiO2@8-HQ-5-SA was characterized by means of SEM, EDX, FT-IR, VSM and BET analyses. Adsorption capacities of 558 mg/g, 680 mg/g and 716 mg/g were achieved for single component toluene, ethylbenzene and xylene, respectively. It was concluded that the adsorption capacities for both binary and ternary components were significantly decreased compared to single component adsorption. The competitive adsorption capacity order of the binary and ternary component VOCs was xylene > ethylbenzene > toluene due to their competitive dominance. The rate-limiting kinetic analysis indicated that the adsorption rates were determined by both the film diffusion and intraparticle diffusion. The analysis of the error metrics demonstrated that the three-parameter isotherm models better described the adsorption data compared to the two-parameter models. In particular, the Toth model provided the closest fit to the experimental equilibrium data. The thermodynamic analysis indicated the spontaneous nature and probability (ΔG° <0), exothermic (ΔH° <0), physical (ΔH° <20 kJ/mol) and a declination in the degree of randomness (ΔS° <0) of the adsorption processes. The reuse efficiency of perlite-Fe3O4@SiO2@8-HQ-5-SA for toluene, ethylbenzene and xylene decreased to only by 88.91%, 88.07% and 87.16% after five recycles. The perlite-Fe3O4@SiO2@8-HQ-5-SA has a significant adsorptive potential compared to other adsorbents reported in the literature, thus it could be recommended as a promising nanoadsorbent for VOCs in industrial processes.

Synthesis of Iron Oxides and Influence on Final Sizes and Distribution in Bacterial Cellulose Applications

Iron oxide nanoparticles have been investigated due to their suitable characteristics for diverse applications in the fields of biomedicine, electronics, water or wastewater treatment and sensors. Maghemite, magnetite and hematite are the most widely studied iron oxide particles and have ferrimagnetic characteristics. When very small, however, these particles have superparamagnetic properties and are called superparamagnetic iron oxide nanoparticles (SPIONs). Several methods are used for the production of these particles, such as coprecipitation, thermal decomposition and microemulsion. However, the variables of the different types of synthesis must be assessed to achieve greater control over the particles produced. In some studies, it is possible to compare the influence of variations in the factors for production with each of these methods. Thus, researchers use different adaptations of synthesis based on each objective and type of application. With coprecipitation, it is possible to obtain smaller, more uniform particles with adjustments in temperature, pH and the types of reagents used in the process. With thermal decomposition, greater control is needed over the time, temperature and proportion of surfactants and organic and aqueous phases in order to produce smaller particles and a narrower size distribution. With the microemulsion process, the control of the confinement of the micelles formed during synthesis through the proportions of surfactant and oil makes the final particles smaller and less dispersed. These nanoparticles can be used as additives for the creation of new materials, such as magnetic bacterial cellulose, which has different innovative applications. Composites that have SPIONs, which are produced with greater rigour with regards to their size and distribution, have superparamagnetic properties and can be used in medical applications, whereas materials containing larger particles have ferromagnetic applications. To arrive at a particular particle with specific characteristics, researchers must be attentive to both the mechanism selected and the production variables to ensure greater quality and control of the materials produced.

Magnetic Nanocomposite Materials Based on Fe3O4 Nanoparticles with Iron and Silica Glycerolates Shell: Synthesis and Characterization

Novel magnetic nanocomposite materials based on Fe3O4 nanoparticles coated with iron and silica glycerolates (MNP@Fe(III)Glyc and MNP@Fe(III)/SiGlyc) were obtained. The synthesized nanocomposites were characterized using TEM, XRD, TGA, VMS, Mössbauer and IR spectroscopy. The amount of iron and silica glycerolates in the nanocomposites was calculated from the Mössbauer spectroscopy, ICP AES and C,H-elemental analysis. Thus, it has been shown that the distribution of Fe in the shell and core for MNP@Fe(III)Glyc and MNP@Fe(III)/SiGlyc is 27:73 and 32:68, respectively. The synthesized nanocomposites had high specific magnetization values and a high magnetic response to the alternating magnetic field. The hydrolysis of shells based on Fe(III)Glyc and Fe(III)/SiGlyc in aqueous media has been studied. It has been demonstrated that, while the iron glycerolates shell of MNP@Fe(III)Glyc is resistant to hydrolysis, the silica glycerolates shell of MNP@Fe(III)/SiGlyc is rather labile and hydrolyzed by 76.4% in 24 h at 25 °C. The synthesized materials did not show cytotoxicity in in vitro experiments (MTT-assay). The data obtained can be used in the design of materials for controlled-release drug delivery.

Toward the Separation of Different Heating Mechanisms in Magnetic Particle Hyperthermia

Magnetic particle hyperthermia (MPH) is a promising method for cancer treatment using magnetic nanoparticles (MNPs), which are subjected to an alternating magnetic field for local heating to the therapeutic range of 41-45 °C. In this window, the malignant regions (i.e., cancer cells) undergo a severe thermal shock while healthy tissues sustain this thermal regime with significantly milder side effects. Since the heating efficiency is directly associated with nanoparticle size, MNPs should acquire the appropriate size to maximize heating together with minimum toxicity. Herein, we report on facile synthetic controls to synthesize MNPs by an aqueous precipitation method, whereby tuning the pH values of the solution (9.0-13.5) results in a wide range of average MNP diameters from 16 to 76 nm. With respect to their size, the structural and magnetic properties of the MNPs are evaluated by adjusting the most important parameters, i.e. the MNP surrounding medium (water/agarose), the MNP concentration (1-4 mg mL^-1), and the field amplitude (20-50 mT) and frequency (103, 375, 765 kHz). Consequently, the maximum heating efficiency is determined for each MNP size and set of parameters, outlining the optimum MNPs for MPH treatment. In this way, we can address the different heat generation mechanisms (Brownian, Néel, and hysteresis losses) to different sizes and separate Brownian and hysteresis losses for optimized sizes by studying the heat generation as a function of the medium viscosity. Finally, MNPs immobilized into agarose solution are studied under low-field MPH treatment to find the optimum conditions for clinical applications.

Magnetic Nanoparticles for Protein Separation and Purification

Proteins are essential for various functions such as brain activity and muscle contraction in humans. Even though food is a source of proteins, the bioavailability of proteins in most foods is usually limited due to matrix interaction with other biomolecules. Thus, it is essential to extract these proteins and provide them as a nutraceutical supplement to maintain protein levels and avoid protein deficiency. Hence, protein purification and extraction from natural sources are highly significant in biomedical applications. Chromatography, crude mechanical disruption, use of extractive chemicals, and electrophoresis are some of the methods applied to isolate specific proteins. Even though these methods possess several advantages, they are unable to extract specific proteins with high purity. A suitable alternative is the use of nanoparticles, which can be beneficial in protein purification and extraction. Notably, magnetic iron and iron-based nanoparticles have been employed in protein extraction processes and can be reused via demagnetization due to their magnetic property, smaller size, morphology, high surface-to-volume ratio, and surface charge-mediated property. This chapter is a summary of various magnetic nanoparticles (MNPs) that can be used for the biomolecular separation of proteins.

Terminal deoxynucleotidyl transferase associated with split G-quadruplex/hemin deoxyribozyme amplification detection for various contaminants in milk based on pregnancy test strip platform

Contaminant residue analysis in milk can provide essential assistance for safety quality and contamination level management of milk production, which is critical for safeguarding public health. In this study, the pregnancy test strip is employed to achieve multiple analytes detection based on the specific recognition of aptamer and terminal deoxynucleotidyl transferase associated with split G-quadruplex/hemin deoxyribozyme system. Through the subsequent enzyme catalyzed reaction, the detection signal can be further amplified to improve the sensitivity. The method does not need to assemble test strip, prepare and purify antibodies/haptens, nor design complex probe sequences. By coupling human chorionic gonadotrophin with DNA probes and combining magnetic separation technology, the targets can be determined via the test strip. Under the optimized conditions, the visual detection limits for mercury ion, bisphenol A, and penicillin are 1, 0.1 and 0.05 nM, respectively. The detection results show that the method displays good accuracy and practicability in spiked milk sample. The method presents a simple scheme, low cost as well as good design versatility, which demonstrates great application prospect for the sensitive, low-cost, and convenient detection of food matrices.

Recent advances in nanomaterials-based optical sensors for detection of various biomarkers (inorganic species, organic and biomolecules)

This review briefly emphasizes the different detection approaches (electrochemical sensors, chemiluminescence, surface-enhanced Raman scattering), functional nanostructure materials (quantum dots, metal nanoparticles, metal nanoclusters, magnetic nanomaterials, metal oxide nanoparticles, polymer-based nanomaterials, and carbonaceous nanomaterials) and detection mechanisms. Further, this review emphasis on the integration of functional nanomaterials with optical spectroscopic techniques for the identification of various biomarkers (nucleic acids, glucose, uric acid, oxytocin, dopamine, ascorbic acid, bilirubin, spermine, serotonin, thiocyanate, Pb²⁺ , Cu²⁺ , Hg²⁺ , F^- , peptides, and cancer biomarkers (mucin 1, prostate specific antigen, carcinoembryonic antigen, CA15-3, human epidermal growth factor receptor 2, C-reactive protein, and interleukin-6). Analytical characteristics of nanomaterials-based optical sensors are summarized in Tables, providing the insights of nanomaterials-based optical sensors for biomarkers detection. Finally, the opportunities and challenges of nanomaterials-based optical analytical approaches for the detection of various biomarkers (inorganic, organic, biomolecules, peptides and proteins) are discussed.