Enzyme mimetic activities of spinel substituted nanoferrites (MFe2O4): A review of synthesis, mechanism and potential applications

Recent advancements in magnetic starch-based composites for biomedical applications: A review

The increasing demand for biomedical materials to address various diseases has highlighted the need for advanced biocompatible materials with improved biofunctionality for smart diagnostics and clinical therapies. Starch, a natural polymer, is an ideal starting material for the development of multifunctional biomedical materials due to its biocompatibility, low toxicity, and biodegradability. However, native starch lacks certain properties, particularly magnetic properties. By strategically modifying the structure of starch or its derivatives and incorporating different types of magnetic nanoparticles (MNPs), magnetic starch-based composites (MSBCs) can be developed. These composites take the advantages of both the magnetic materials and natural polysaccharides, enhancing the mechanical strength of starch and imparting additional properties, such as magneto-thermal effects, targeting ability, stimulus-responsive drug delivery, and easy separation. As a result, MSBCs have widespread applications in fields such as wound dressing and magneto-thermal therapy. This review highlights the types of MSBCs, their synthesis methods, and their current applications in biomedicine. Additionally, this review describes the major challenges faced by MSBCs in biomedical applications and provides an outlook on their potential for further development. This review aims to improve the understanding of magnetic starches and optimize their synthetic strategies, positioning MSBCs as promising platforms for biomedical applications.

Hydrogel patch doped with nanoenzyme for SERS detection of hydrogen peroxide in complex body fluids

Abnormally elevated levels of H2O2 in body fluids are strongly correlated with various diseases, particularly cancers. Consequently, there is a significant need to develop a simple and efficient method for direct detection of H2O2 in body fluids. This study presents an economical and feasible hydrogel patch doped with nanoenzyme, specifically gold nanoparticles assembled on the surface of magnetic nanoparticles (Au@Fe3O4 NPs), as a sensing platform for H2O2 in complex body fluids. The hydrogel surface-enhanced Raman spectroscopy (SERS) patch demonstrates ultra-high sensitivity for H2O2 in vitro with a detection limit of 10 nM, which is attributed to the excellent catalytic efficiency of Au@Fe3O4 NPs and the rich distribution of SERS "hot spots" on the nanoenzyme. Notably, the hydrogel SERS patch exhibits superior specificity, repeatability, and background-free detection of H2O2 in complex body fluids without pre-treatment. Importantly, the H2O2 levels within cancerous cells were observed to gradually increase during the cell death process, as measured using the hydrogel SERS patch developed for practical application. This SERS patch provides a promising, cost-effective strategy for H2O2 detection in complex samples such as body fluids, food, and environmental samples in future applications.

A critical review on metal organic frameworks (MOFs)-based sensors for foodborne pathogenic bacteria detection

The pervasive threat of foodborne pathogenic bacteria necessitates advancements in rapid and reliable detection methods. Traditional approaches suffer from significant limitations including prolonged processing times, limited sensitivity and specificity. This review comprehensively examines the integration of metal organic frameworks (MOFs) with sensor technologies for the enhanced detection of foodborne pathogens. MOFs, with their unique properties such as high porosity, tunable pore sizes, and ease of functionalization, offer new avenues for sensor enhancement. This paper provides a comprehensive analysis of recent developments in MOFs-based sensors, particularly focusing on electrochemical, fluorescence, colorimetric, and surface-enhanced Raman spectroscopy sensors. We have provided a detailed introduction for the operational principles of these sensors, highlighting the role of MOFs play in enhancing their performance. Comparative analyses demonstrate MOFs' superior capabilities in enhancing signal response, reducing response time, and expanding detection limits. This review culminates in presenting MOFs as transformative materials in the detection of foodborne pathogens, paving the way for their broader application in ensuring food safety.

MnFe2O4-loaded bamboo pulp carbon-based aerogel composite: synthesis, characterization and adsorption behavior study for heavy metals removal

Heavy metal wastewater is a direct threat to the ecological environment and human health because it is highly toxic at low concentrations. Therefore, it is very important to explore and develop efficient wastewater treatment agents. MnFe2O4-loaded bamboo pulp carbon-based aerogel (MCA) is prepared by directional freeze-drying and carbonization. SEM, TEM, XPS, XRD, BET and FTIR are used to evaluate the physical and chemical properties of MCA. Meanwhile, the adsorption performances of MCA on Pb2+, Cu2+ and Cd2+ are also studied by adsorption kinetics, isothermal curves and thermodynamics. The results show that the adsorption process involves chemical adsorption and physical adsorption, and the adsorption process is a spontaneous endothermic process. The maximum adsorption capacities of MCA for Pb2+, Cu2+ and Cd2+ obtained in the adsorption isotherm experiments were 74.38, 84.21 and 73.63 mg g-1, respectively, showing excellent adsorption performance for Pb2+, Cu2+ and Cd2+. Therefore, the MCA has potential application for wastewater purification of heavy metals containing Pb2+, Cu2+ and Cd2+, meanwhile, this study provides some guidance for the design and application of microspheres for the separation and removal of Pb2+, Cu2+ and Cd2+.

Iron oxide nanozymes as versatile analytical tools: an overview of their application as detection technique

Iron oxide nanozymes (IONzymes) have become fundamental components in various analyte detection methodologies such as colorimetric, electrochemistry, fluorescence and luminescence. Their tunability, stability and the possibility of modification, alongside their ability to mimic the catalytic properties of natural enzymes like peroxidase, render them invaluable in analytical chemistry. This review explores the diverse applications of IONzymes across analytical chemistry, with a particular highlighting on their roles in different detection techniques and their potential in biomedical and diagnostic applications. This information would be valuable for researchers and practitioners in the fields of analytical chemistry, biochemistry, biotechnology and materials science who are interested in applying IONzymes in their work. In essence, this review article on iron oxide nanozymes in analytical chemistry would serve as a valuable resource for researchers, educators and industry professionals, offering insights, guidance and inspiration for further study and application of this promising class of nanomaterials.

Facile one-pot synthesis of the mesoporous chitosan-coated cobalt ferrite nanozyme as an antibacterial and MRI contrast agent

Cobalt ferrite (CoFe) nanoparticles (NPs) with appropriate physicochemical and biological properties have attracted great attention for biomedical applications. In the present study, chitosan-coated mesoporous CoFe (CoFeCH) NPs were synthesized using a facile one-step hydrothermal method and fully characterized using FE-SEM, EDS, BET, FTIR spectroscopy, DLS, TGA, XRD, and VSM. The spherical, highly colloidal, and monodispersed CoFeCH NPs with an average hydrodynamic size of 177.9 nm, PDI of 0.238 and zeta potential value of -33 represented a high saturation magnetization value of 59.37 emu g-1. N2 adsorption-desorption analysis confirmed the mesoporous structure of CoFeCH NPs with a type IV isotherm, calculated specific surface area of 89.583 m2 g-1 and total pore volume of 0.3668 cm3 g-1. CoFeCH NPs exhibited high antibacterial effects on S. aureus and E. coli, comparable with standard antibiotics, while CH-coating led to higher biocompatibility of CoFe NPs on human cells in vitro. CoFeCH NPs also showed significant peroxidase activity with a Km value of 14.37 and specific activity of 0.632 mmol min-1. CoFeCH NPs were successfully used as a MRI contrast agent with an R2 value of 91.3 mM-1 s-1. The overall results indicated the high potential of synthesized CoFeCH NPs by the present method for biomedical applications, especially as an antibacterial and MRI contrast agent.

Single-Atom-Based Nanoenzyme in Tissue Repair

Since the discovery of ferromagnetic nanoparticles Fe3O4 that exhibit enzyme-like activity in 2007, the research on nanoenzymes has made significant progress. With the in-depth study of various nanoenzymes and the rapid development of related nanotechnology, nanoenzymes have emerged as a promising alternative to natural enzymes. Within nanozymes, there is a category of metal-based single-atom nanozymes that has been rapidly developed due to low cast, convenient preparation, long storage, less immunogenicity, and especially higher efficiency. More importantly, single-atom nanozymes possess the capacity to scavenge reactive oxygen species through various mechanisms, which is beneficial in the tissue repair process. Herein, this paper systemically highlights the types of metal single-atom nanozymes, their catalytic mechanisms, and their recent applications in tissue repair. The existing challenges are identified and the prospects of future research on nanozymes composed of metallic nanomaterials are proposed. We hope this review will illuminate the potential of single-atom nanozymes in tissue repair, encouraging their sequential clinical translation.

Potential Strategy to Control the Organic Components of Condensable Particulate Matter: A Critical Review

More and more attention has been paid to condensable particulate matter (CPM) since its emissions have surpassed that of filterable particulate matter (FPM) with the large-scale application of ultralow-emission reform. CPM is a gaseous material in the flue stack but instantly turns into particles after leaving the stack. It is composed of inorganic and organic components. Organic components are an important part of CPM, and they are an irritant, teratogenic, and carcinogenic, which triggers photochemical smog, urban haze, and acid deposition. CPM organic components can aggravate air pollution and climate change; therefore, consideration should be given to them. Based on existing methods for removing atmospheric organic pollutants and combined with the characteristics of CPM organic components, we provide a critical overview from the aspects of (i) fundamental cognition of CPM, (ii) common methods to control CPM organic components, and (iii) catalytic oxidation of CPM organic components. As one of the most encouraging methods, catalytic oxidation is discussed in detail, especially in combination with selective catalytic reduction (SCR) technology, to meet the growing demands for multipollutant control (MPC). We believe that this review is inspiring for a fuller understanding and deeper exploration of promising approaches to control CPM organic components.

The Cd immobilization mechanisms in paddy soil through ureolysis-based microbial induced carbonate precipitation: Emphasis on the coexisting cations and metatranscriptome analysis

Microbial induced carbonate precipitation (MICP) can immobilize metals and reduce their bioavailability. However, little is known about the immobilization mechanism of Cd in the presence of soil cations and the triggered gene expression and metabolic pathways in paddy soil. Thus, microcosmic experiments were conducted to study the fractionation transformation of Cd and metatranscriptome analysis. Results showed that bioavailable Cd decreased from 0.62 to 0.29 mg/kg after 330 d due to the MICP immobilization. This was ascribed to the increase in carbonate bound, Fe-Mn oxides bound, and residual Cd. The underlying immobilization mechanisms could be attributed to the formation of insoluble Cd-containing precipitates, the complexation and lattice substitution with carbonate and Fe, Mn and Al (hydr)oxides, and the adsorption on functional group on extracellular polymers of cell. During the MICP immobilization process, up-regulated differential expression urease genes were significantly enriched in the paddy soil, corresponding to the arginine biosynthesis, purine metabolism and atrazine degradation. The metabolic pathway of bacterial chemotaxis, flagellum assembly, and peptidoglycan biosynthesis and the expression of cadA gene related to Cd excretion enhanced Cd resistance of soil microbiome. Therefore, this study provided new insights into the immobilization mechanisms of Cd in paddy soils through ureolysis-based MICP process.

One-pot synthesized copper-imidazole-2-carboxaldehyde complex material with oxidase-like activity for the colorimetric detection of glutathione and ascorbic acid

Due to the copper (Cu) active sites, its complexes with oxidase-like activity have superior catalytic properties, which can catalyze a series of specific substrates like 3,3',5,5'-tetramethylbenzidine (TMB), producing colorimetric reactions for the detection of different reducing small-molecule compounds. Attribute to the competitive coordination effects between water molecules and central Cu ions, most of the Cu complexes can hardly be used in the pure aqueous reaction system. In this study, a Cu-based material (Cu-imidazole-2-carboxaldehyde, Cu-ICA) was prepared using copper ions and ICA through a one-step process in the water solution. After the morphology of the material being characterized, the mimetic enzyme behavior of the Cu-ICA was demonstrated through the TMB oxidation. Compared to the other reported oxidase-like mimics, Cu-ICA has better aqueous stability and oxidase-like activity, and shows a higher vmax. Furthermore, basing on the oxidase-like activity of Cu-ICA, a colorimetric method was developed for the ascorbic acid and glutathione detections with linear ranges of 0.5-5 μM and 0.5-4 μM, and limit of detection of 0.1304 μM and 0.097 μM, respectively. Owing to its excellent aqueous stability and oxidase-like activity, Cu-ICA has bright application prospects in the analysis of reducing small-molecule compounds.

Advances in the application of metal-organic framework nanozymes in colorimetric sensing of heavy metal ions

Nanozymes, which can be defined as nanomaterials with excellent catalytic function, are well known to the scientific community due to their distinct merits, such as low cost and high stability, which render them preferable to natural enzymes. As porous organic-inorganic coordination materials, metal-organic frameworks (MOFs) possess a large number of active sites and thus can effectively mimic the properties of natural enzymes. Recently, MOF-based nanozymes have also exhibited good application potential for the analysis of heavy metal ions. In comparison to the traditional detection methods for heavy metal ions, nanozyme-based colorimetric sensing permits intuitive visual analysis by using relatively simple instruments, facilitating rapid and simple on-site screening. In this minireview, the preparation of MOF-based nanozymes and the different nanozyme activity types are briefly described, such as peroxidase-like and oxidase-like, and the relevant catalytic mechanisms are elaborated. Based on this, different response mechanisms of MOF-based colorimetric methods to heavy metal ions, such as turn-off, turn-on, and turn-off-on, are discussed. In addition, the colorimetric sensing applications of MOF-based nanozymes for the detection of heavy metal ions are summarized. Finally, the current research status of MOF-based nanozymes and the future development direction are discussed.

Ultrasonic-assisted decoration of Ag2WO4, AgI, and Ag nanoparticles over tubular g-C3N4: Plasmonic photocatalysts for impressive removal of tetracycline under visible light

The development of an efficient, eco-friendly, and low-cost photocatalyst is essential for addressing environmental and energy crises. In this regard, we report novel plasmonic photocatalysts through adorning tubular g-C₃N₄ with Ag₂WO₄, Ag, and AgI nanoparticles (TGCN/Ag/Ag₂WO₄/AgI) fabricated via a facile ultrasonic-irradiation procedure. The TGCN/Ag/Ag₂WO₄/AgI (20%) nanocomposite presented the excellent photocatalytic ability for removal of tetracycline hydrochloride under visible light, which was almost 45.6, 4.03, and 1.32 times more than GCN, TGCN, and TGCN/Ag/Ag₂WO₄ (20%) photocatalysts, respectively. Interestingly, the photocatalyst displayed impressive ability for the degradations of amoxicilline, rhodamine B, methyl orange, fuchsine, and methylene blue, which was 14.7, 52.2, 9.8, 13.2, and 7.46 times as much as pure GCN. The outcomes of DRS, PL, EIS, and photocurrent density analyses proved that the impressive activity could be related to the highly promoted harvesting of visible light, segregation of charge carriers, and improved charge migrations. In addition, trapping tests exhibited that ^•O₂^- and h⁺ were active species in the photocatalysis process.

Colorimetric assay for the detection of dopamine using bismuth ferrite oxide (Bi2Fe4O9) nanoparticles as an efficient peroxidase-mimic nanozyme

This work describes the preparation of ternary bismuth ferrite oxide nanoparticles (Bi₂Fe₄O₉ NPs) with an enzyme mimetic activity for dopamine (DA) qualitative and quantitative detection. Bi₂Fe₄O₉ NPs were prepared using a facile, low cost, and one-pot hydrothermal treatment. The chemical composition, morphology, and optical properties of Bi₂Fe₄O₉ nanozyme were characterized using different techniques such as Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction pattern (XRD), X-ray photoelectron spectroscopy (XPS), thermo-gravimetric analysis (TGA), dynamic light scattering (DLS), field-emission scanning electron microscopy (FESEM) imaging, FESEM-energy dispersive X-ray spectroscopy (EDS), UV-vis absorption, and fluorescence emission spectroscopy. Bi₂Fe₄O₉ NPs were utilized to catalyze the oxidation of a typical chromogenic peroxidase substrate, 3,3',5,5'-tetramethylbenzidine (TMB), to form the blue-colored oxidized product (oxTMB), in the presence of hydrogen peroxide (H₂O₂). All reactions occurred in acetate buffer solution (pH 3.5) to generate hydroxyl radicals (^•OH) and the kinetics were followed by UV-vis absorbance at 654 nm. The steady-state kinetic parameters were obtained from the Michaelis-Menten equation and exhibited a good catalytic efficiency of Bi₂Fe₄O₉ NPs as enzyme mimetics. Michaelis-Menten constant (K_m) values were estimated as 0.07 and 0.73 mM for TMB and H₂O₂, respectively. The presented method is efficient, rapid, cost-effective, and sensitive for the colorimetric detection of dopamine with a linear range (LR) from 0.15 to 50 μM and a detection limit (LOD) of 51 nM. The proposed colorimetric sensor was successfully applied for the detection of different concentrations of dopamine in spiked fetal bovine serum (FBS) and horse serum (HS) samples. It is anticipated that Bi₂Fe₄O₉ nanozyme holds great potential in biomedical analysis and diagnostic applications of dopamine-related diseases.

A controllable one-pot hydrothermal synthesis of spherical cobalt ferrite nanoparticles: synthesis, characterization, and optical properties

We herein report the controllable synthesis of spherical cobalt ferrite nanoparticles with average crystallite size in the range of 3.6–12.9 nm using a facile, eco-friendly, hydrothermal method. The hydrothermal treatment was carried out by utilizing cobalt nitrate, ferric nitrate, and ammonium hydroxide in the presence and absence of Arabic gum as a surfactant agent. The purity and crystallinity of the products were tuned by varying reaction conditions such as reaction time (0.5–8 h), reaction temperature (120–180 °C), percentage of ethylene glycol (0–100% (v/v)), pH (8–9.6), and amount of Arabic gum (0–2 g). We characterized the prepared products using X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), Fourier transform infrared spectroscopy (FT-IR), high-resolution transmission electron microscopy (HR-TEM), energy-dispersive X-ray spectroscopy analysis (EDS), selected area electron diffraction (SAED) patterns, and UV-visible diffuse reflectance spectra (DRS). The optimal hydrothermal treatment was performed at 180 °C and pH 9.6 for 4 h in aqueous media. The results also revealed that the as-prepared spinel cobalt ferrite nanoparticles have an estimated optical band gap energy in the range of ca. 1.6–1.9 eV, indicating the semiconducting characteristics of the products.

A controllable synthesis of spherical cobalt ferrite nanoparticles with average crystallite size in the range of 3.6–12.9 nm using a facile, eco-friendly, hydrothermal method.

Chemiluminescent magnetic nanoparticles with good catalytic activity and rapid separation capability and sensitive sensing for H2O2

It is of considerable importance to develop chemiluminescent functionalized nanomaterials (CF-NMs) with good catalytic activity, high chemiluminescence (CL) efficiency and good stability, and rapid magnetic separation capability, achieving excellent performance in CL biosensing. In this study, N-(4-aminobutyl)-N-ethylisoluminol (ABEI)-functionalized CuFe2O4 magnetic nanomaterial (ABEI/CuFe2O4) with high catalytic activity was synthesized by virtue of a solvothermal and post-functionalization method. ABEI/CuFe2O4 showed outstanding CL properties, superior to ABEI-CuFe2O4 in liquid phase. This reveals that the immobilization of ABEI on the surface of CuFe2O4 exhibits unique heterogeneous catalytic property. The catalytic ability of CuFe2O4 was better than that of CoFe2O4, ZnFe2O4, MnFe2O4, and NiFe2O4. It is suggested that the peroxide-like activity as well as Cu2+ and Cu0 enriched on the surface of ABEI/CuFe2O4 opened up a dual route for synergistic catalysis of H2O2. ABEI/CuFe2O4 also demonstrated good superparamagnetism and magnetic separation could be carried out in 2 min, which is advantageous for the separation and purification of ABEI/CuFe2O4 during the synthetic procedures and bioassays. Owing to the sensitive response of ABEI/CuFe2O4 to H2O2, an enzyme-free sensor was developed for the detection of H2O2 with a wide linear range over 5 orders of magnitude of H2O2 concentrations and a low detection limit of 5.6 nM. The as-developed sensor is sensitive, stable, and convenient. This work provides a new family member of nanomaterials with good magnetism and CL activity as well as good stability. The developed ABEI/CuFe2O4 shows great prospects in biocatalysis, bioassays, biosensing, and bioimaging, etc.

A facile green synthesis of MgCoFe2O4 nanomaterials with robust catalytic performance in the synthesis of pyrano[2,3-d]pyrimidinedione and their bis-derivatives

In this study, an efficient, rapid and simple plant-mediated green sol-gel auto-combustion procedure was presented to synthesis magnesium-cobalt ferrite (MgCoFe2O4) nanocatalyst using an aqueous extract of apple skins as a chelating/combustion agent. The catalyst was assessed by multiple techniques, including FT-IR, XRD, FE-SEM, EDS, elemental mapping, TGA-DTA and VSM. Then, the catalytic potential of the as-prepared MgCoFe2O4 nanocatalyst was examined in the three-component condensation reaction of 1,3-dimethyl barbituric acid, aldehydes and malononitrile for the one-pot synthesis of pyrano[2,3-d]pyrimidinedione and their bis-derivatives. The obtained results indicated the excellent catalytic activity of the MgCoFe2O4 in the three-component reaction. The high catalytic activity of these nanomaterials could be attributed to the synergistic electronic effect between nanoparticles, which showcased the enormous potential of multi-metallic nanomaterials in the catalysis field. More importantly, MgCoFe2O4 showed excellent magnetic properties, and it could be successfully separated and recovered by applying an external magnetic for further reuses. To the best of our knowledge, green synthesis of MgCoFe2O4 mediated by aqueous plant extract was reported here for the first time, and this work, therefore, can open up a new insight in the course of design, green synthesis and application of excellent green nanocatalyst for the sustainable processes. MgCoFe2O4 as a magnetically recyclable heterogeneous catalyst, has been synthesized through plant-mediated procedure using an aqueous extract of apple skins.

Spinel ferrites (MFe2O4): Synthesis, improvement and catalytic application in environment and energy field

To develop efficient catalysts is one of the major ways to solve the energy and environmental problems. Spinel ferrites, with the general chemical formula of MFe₂O₄ (where M = Mg²⁺, Co²⁺, Ni²⁺, Zn²⁺, Fe²⁺, Mn²⁺, etc.), have attracted considerable attention in catalytic research. The flexible position and valence variability of metal cations endow spinel ferrites with diverse physicochemical properties, such as abundant surface active sites, high catalytic activity and easy to be modified. Meanwhile, their unique advantages in regenerating and recycling on account of the magnetic performances facilitate their practical application potential. Herein, the conventional as well as green chemistry synthesis of spinel ferrites is reviewed. Most importantly, the critical pathways to improve the catalytic performance are discussed in detail, mainly covering selective doping, site substitution, structure reversal, defect introduction and coupled composites. Furthermore, the catalytic applications of spinel ferrites and their derivative composites are exclusively reviewed, including Fenton-type catalysis, photocatalysis, electrocatalysis and photoelectro-chemical catalysis. In addition, some vital remarks, including toxicity, recovery and reuse, are also covered. Future applications of spinel ferrites are envisioned focusing on environmental and energy issues, which will be pushed by the development of precise synthesis, skilled modification and advanced characterization along with emerging theoretical calculation.

Trigonal Planar Iron(II) and Cobalt(II) Complexes Containing [RS(NtBu)3]n- (R = NtBu, n = 2; CH2PPh2, n = 1) as Acute Bite-Angle Chelating Ligands: Soft P Donor Proves Beneficial to Magnetic Co Species

We prepared four new complexes, 4a,b and 5a,b, from polyimido sulfur-centered ligands with Fe^II and Co^II amides. Their molecular structures were elucidated by single-crystal X-ray diffraction. Cobalt magnetic investigations and multiconfigurational calculations provided insight into magneto-structural correlations between the acute N,N' chelating bite angle and P-side arm donation. The deviation from an ideal trigonal planar geometry and the magnetic performance correlated in an unprecedented manor. Mononuclear cobalt species 4b and 5b showed slow magnetic relaxation under a small applied dc field with energy barriers of up to 33.0 and 21.9 cm^-1, respectively. Although they possess some of the largest zero-field splitting parameters among three-coordinate cobalt single-ion magnets, both theory and experiment suggest that the high rhombicity (E/D) hampers large effective energy barriers to spin reversal at zero field from being obtained.

Recent Advances in Synthesis and Applications of MFe2O4 (M = Co, Cu, Mn, Ni, Zn) Nanoparticles

In the last decade, research on the synthesis and characterization of nanosized ferrites has highly increased and a wide range of new applications for these materials have been identified. The ability to tailor the structure, chemical, optical, magnetic, and electrical properties of ferrites by selecting the synthesis parameters further enhanced their widespread use. The paper reviews the synthesis methods and applications of MFe₂O₄ (M = Co, Cu, Mn, Ni, Zn) nanoparticles, with emphasis on the advantages and disadvantages of each synthesis route and main applications. Along with the conventional methods like sol-gel, thermal decomposition, combustion, co-precipitation, hydrothermal, and solid-state synthesis, several unconventional methods, like sonochemical, microwave assisted combustion, spray pyrolysis, spray drying, laser pyrolysis, microemulsion, reverse micelle, and biosynthesis, are also presented. MFe₂O₄ (M = Co, Cu, Mn, Ni, Zn) nanosized ferrites present good magnetic (high coercivity, high anisotropy, high Curie temperature, moderate saturation magnetization), electrical (high electrical resistance, low eddy current losses), mechanical (significant mechanical hardness), and chemical (chemical stability, rich redox chemistry) properties that make them suitable for potential applications in the field of magnetic and dielectric materials, photoluminescence, catalysis, photocatalysis, water decontamination, pigments, corrosion protection, sensors, antimicrobial agents, and biomedicine.

Biosensing platform on ferrite magnetic nanoparticles: Synthesis, functionalization, mechanism and applications

Ferrite magnetic nanoparticles (FMNPs) are gaining popularity to design biosensors for high-performance clinical diagnosis. The fusion of information shows that FMNPs based biosensors require well-tuned FMNPs as detection probes to produce large and specific biological signals with minimal non-specific binding. Nevertheless, there is a noticeable lacuna of information to solve the issues related to suitable synthesis route, particle size reduction, functionalization, sensitivity towards targeted intercellular biological tiny particles, and lower signal-to-noise ratio. Therefore it allows exploring unique characteristics of FMNPs to design a suitable sensing device for intracellular measurements and diseases detection. This review focuses on the extensively used synthesis routes, their advantages and limitations, crystalline structure, functionalization, along with recent applications of FMNPs in biosensors, taking into consideration their analytical figures of merit and range of linearity. This work also addresses the current progress, key factors for sensitivity, selectivity and productivity improvement along with the challenges, future trends and perspectives of FMNPs based biosensors.

Magnetic nanomaterials with unique nanozymes-like characteristics for colorimetric sensors: A review

Colorimetric sensors for the rapid detection of numerous analytes have been widely applied in many fields such as biomedicine, food industry and environmental science due to their highly sensitive and selective response, easy operation and visual identification by naked eyes. In this review, the recent progress of the colorimetric sensors based on the magnetic nanomaterials with unique nanozymes-like catalytic activity (magnetic nanozyme) and their colorimetric sensing applications are presented. Emerging magnetic nanozyme-based colorimetric sensors, such as metal oxide/sulfides-based, metal-based, carbon-based, and aptamer-conjugated magnetic nanomaterials, offer many desirable features for target analytes detection. And due to the unique nanoscale physical-chemical properties, magnetic nanozymes have been used to mimic the catalytic activity of natural enzymes such as peroxidases, oxidases and catalases. This review also highlights the catalytic mechanisms of enzyme-like reactions, and promising colorimetric sensing system for the detection of chemical compounds like H₂O₂, pesticide, ascorbic acid, dopamine, tetracyclines, perfluorooctane sulfonate, phenolic compounds, heavy metal ion and sulfite have been deeply discussed. In addition, the remaining challenges and future directions in utilizing magnetic nanozyme for colorimetric sensors are addressed.

Nanozyme based on CoFe2O4 modified with MoS2 for colorimetric determination of cysteine and glutathione

A nanozyme based on CoFe₂O₄ modified with MoS₂ was constructed for colorimetric determination of cysteine (Cys) and glutathione (GSH). Firstly, ferrite CoFe₂O₄ is synthesized, and it is then modified by MoS₂ to form a flower-like polymer (MoS₂@CoFe₂O₄). In the presence of H₂O₂, a redox interaction takes place, and the resulting hydroxyl promoted a colorimetric conversion from colorless to blue in the presence of 3,3',5,5'-tetramethylbenzidine (TMB). However, once Cys or GSH is added, they are capable to compete with the interaction of the hydroxyl with TMB, resulting in an inhibition of the colorimetric conversion. The colorimetric distinction is sensitive to the amount of target. The results obtained proved that the catalytic efficiency of MoS₂@CoFe₂O₄ is 4.4-fold and 1.8-fold to that of MoS₂ and CoFe₂O₄. Meanwhile, the K_m values to TMB and H₂O₂ are 0.067 and 0.048 mM, respectively, which are 6.5-fold and 77-fold, respectively smaller than those of natural peroxidase such as HPR. This indicates that the MoS₂@CoFe₂O₄ possesses a favorable interaction affinity. Additionally, the colorimetric distinction caused by the competition between TMB and cysteine or glutathione is obvious. The signal responses to cysteine and glutathione are linear in the range 0.5~15 μM and 0.5~35 μM, and the LODs are 0.10 and 0.21 μM, respectively. In practical assay of Cys in serum, the RSD of the sample tests is 4.6%, and the recoveries for the spiked assays are 95.3% and 96.0% with the RSD of 2.1% and 4.2%, respectively.

Artificial Bifunctional Photozyme of Glucose Oxidase-Peroxidase for Solar-Powered Glucose-Peroxide Detection in a Biofluid with Resorcinol-Formaldehyde Polymers

Photozymes or artificial photosynthesis based on alternative natural enzymes is vital for the sustainable development of next-generation healthcare, energy, and materials science. Herein, we report resorcinol-formaldehyde (RF) resins as a solar-driven metal-free bifunctional glucose oxidase-peroxidase stand-alone photozyme for the colorimetric dual detection of hydrogen peroxide and glucose. The π-bond conjugated benzenoid-ortho/para quinoid RF polymers are efficient for glucose oxidation and hydrogen peroxide reduction with concurrent 3,3',5,5'-tetramethylbenzidine oxidation under natural sunlight. The photoinduced colorimetric process could detect H₂O₂ up to 3.5 μM at 652 nm with the linear range of 0.1-2 mM. A limit of detection of 9.2 μM was exhibited by the system while measuring glucose with a linearity from 0.2 to 8.5 mM. The formation of hydroxyl radicals (^•OH) from glucose oxidation reactions was evidenced by spin trapping electron paramagnetic resonance studies conducted herein. The results indicated that RF resins possessed strong intrinsic glucose oxidase and peroxidase (POx)-like activity under natural sunlight with promising storage and operation. This simple photozyme will definitely have potential uses in biomimetic solar-driven catalysis, bioenergy, and biomedicine.

Non-enzymatic electrochemical approaches to cholesterol determination

Cholesterol plays a vital role in a human body. It is known as one of the most important sterols, because it forms cell walls and participates in signal transduction. Moreover, cholesterol was recognized as biomarker of cardiovascular diseases and of some metabolic disorders. As a result, cholesterol blood levels should be controlled in a variety of diseases such as ischemic heart disease, cerebrovascular ischemia, stroke, hypertension, type II diabetes, and many others. Hence, the accurate cholesterol quantification plays an important role in diagnosis and treatment of these diseases. Modern voltammetric and amperometric methods are increasingly used for cholesterol monitoring. Consequently, the problem of electrode fabrication for cholesterol detection has high importance for clinical tests. Novel electrode materials initiated the fast growth of electrochemical biosensors. Biomaterials are still the most frequently used modifiers for cholesterol sensors due to their high selectivity. However, biomaterials have low stability complicating their practical applications. This fact is crucial for analytical parameters such as limit of detection (LOD) and sensitivity. Therefore, nanomaterials are used to eliminate disadvantages of biomaterials and to improve sensors performance by increasing the electrode surface, conductivity and sensitivity. This review is focused on the use of non-enzymatic electrodes for cholesterol quantification and on different approaches to their fabrication. Firstly, the necessity and role of modifier is discussed. Afterwards, the advantages and disadvantages of currently used modifiers are critically compared together with all aspects and approaches to sensors fabrication. Finally, the prospects of non-enzymatic electrodes application for cholesterol sensors engineering are summarised.

A nanocomposite of NiFe2O4-PANI as a duo active electrocatalyst toward the sensitive colorimetric and electrochemical sensing of ascorbic acid

A non-enzymatic ascorbic acid sensor using a nickel ferrite/PANI (NF-PANI) nanocomposite and based on colorimetric and electrochemical sensing methods was investigated in this study. The nanocomposite was prepared by an in situ polymerization and utilized as an electrocatalyst to sense ascorbic acid (AA) through the peroxidase mimic sensing of H₂O₂ in the presence of 3,5,3,5-tetramethylbenzidine (TMB) as a coloring agent. It was also utilized to detect AA present in real samples prepared from fruit extracts, commercial beverages, and vitamin-C tablets. The limit of detection (LoD) for AA sensing by the peroxidase mimic method was found to be 232 nM. The relative standard deviation (RSD) calculated for analysis of the real samples analysis ranged from 1.7-3.2%. Similarly, the electrochemical sensing of AA by NF-PANI was examined by cyclic voltammetric, chronoamperometric, and differential pulse voltammetric analyses. The LoD for the electrochemical method applied to AA sensing was 423 nM. The nanocomposite functioned as an effective electrocatalytic sensing agent in both methods to selectively detect AA due to the combined effect of NF and PANI. Thus, it was shown that the nanocomposites could be utilized for the laboratory-based detection of AA by various methods and could give rapid results.

Atomic engineering of single-atom nanozymes for enzyme-like catalysis

Enzyme mimics, especially nanozymes, play a crucial role in replacing natural enzymes for diverse applications related to bioanalysis, therapeutics and other enzyme-like catalysis. Nanozymes are catalytic nanomaterials with enzyme-like properties, which currently face formidable challenges with respect to their intricate structure, properties and mechanism in comparison with enzymes. The latest emergence of single-atom nanozymes (SAzymes) undoubtedly promoted the nanozyme technologies to the atomic level and provided new opportunities to break through their inherent limitations. In this perspective, we discuss key aspects of SAzymes, including the advantages of the single-site structure, and the derived synergetic enhancements of enzyme-like activity, catalytic selectivity and the mechanism, as well as the superiority in biological and catalytic applications, and then highlight challenges that SAzymes face and provide relevant guidelines from our point of view for the rational design and extensive applications of SAzymes, so that SAzyme may achieve its full potential as the next-generation nanozyme.

Magnetism in drug delivery: The marvels of iron oxides and substituted ferrites nanoparticles

In modern drug delivery, seeking a drug delivery system (DDS) with a modifiable skeleton for proper targeting of loaded actives to specific sites in the body is of extreme importance for a successful therapy. Magnetically guided nanosystems, where particles such as iron oxides are guided to specific regions using an external magnetic field, can provide magnetic resonance imaging (MRI) while delivering a therapeutic payload at the same time, which represents a breakthrough in disease therapy and make MNPs excellent candidates for several biomedical applications. In this review, magnetic nanoparticles (MNPs) along with their distinguishable properties, including pharmacokinetics and toxicity, especially in cancer therapy will be discussed. The potential perspective of using other elements within the MNP system to reduce toxicity, improve pharmacokinetics, increase the magnetization ability, improve physical targeting precision and/or widen the scope of its biomedical application will be also discussed.

Recyclable MFe2O4 (M = Mn, Zn, Cu, Ni, Co) coupled micro-nano bubbles for simultaneous catalytic oxidation to remove NO x and SO2 in flue gas

NO x can be efficiently removed by micro-nano bubbles coupling with Fe3+ and Mn2+, but the catalyst cannot be reused and the adsorption wastewater should be treated. This work developed a new technology that uses micro-nano bubbles and recyclable MFe2O4 to simultaneously remove NO x and SO2 from flue gas, and clarified the effectiveness and reaction mechanism. MFe2O4 (M = Mn, Zn, Cu, Ni and Co) prepared by a hydrothermal method was characterized. The results show that MFe2O4 can be activated to produce ˙OH which can accelerate the oxidation absorption of NO x . Compared with no catalyst, the NO x conversion rate increased from 32.85% to 83.88% in the NO x -SO2-MFe2O4-micro-nano bubble system, while the removal rate of SO2 can reach 100% at room temperature. The catalytic activities of MFe2O4 showed the following trend: CuFe2O4 > ZnFe2O4 > MnFe2O4 > CoFe2O4 > NiFe2O4. The results provide a new idea for the application of advanced oxidation processes in flue gas treatment.

Bimetallic nickel-ferrite nanorod particles: greener synthesis using rosemary and its biomedical efficiency

Nickel-ferrite (NiFe₂O₄) nanorods particles (NRP) was biosynthesised for the first time by the Rosemary Extract. The NRP was fully characterised, including the type, nanostructure and physicochemical properties of using XRD, HRTEM, FeSEM, XPS, FTIR and VSM. TEM confirmed rod-shaped nano-sized particles with average sizes ranging from 10 nm to 28 nm. The EDAX Analysis showed the presence of iron, nickel, oxygen, and carbon. XRD analysis confirmed the synthesis of NiFe₂O₄ crystals. XPS curves showed photoelectron for iron, oxygen and nickel. EDS showed the atomic, weight percentages ratios of Ni(12%): Fe(24%) and: O(48) are close to the theoretical value (Ni: Fe:O = 1:2:4), of bimetallic magnetic NiFe₂O₄ NRP. NiFe₂O₄ NRP had cytotoxicity effect on MCF-7 cells survival which suggests that NiFe₂O₄ NRP can be used as a new class of anticancer agent in design novel cancer therapy research.

Metal–oxygen clusters as peroxidase mimics for their multifarious applications in colorimetric sensors

Metal–oxygen cluster (Fe₂₈) was certified to own inherent peroxidase-like performance, which displayed multi-functional applications in H₂O₂, glucose and dopamine detection.

A cobalt-doped iron oxide nanozyme as a highly active peroxidase for renal tumor catalytic therapy

The Fe₃O₄ nanozyme, the first reported nanozyme with intrinsic peroxidase-like activity, has been successfully employed for various diagnostic applications. However, only a few studies have been reported on the therapeutic applications of the Fe₃O₄ nanozyme partly due to its low affinity to the substrate H₂O₂. Herein, we report a new strategy for improving the peroxidase-like activity and affinity of the Fe₃O₄ nanozyme to H₂O₂ to generate reactive oxygen species (ROS) for kidney tumor catalytic therapy. We showed that cobalt-doped Fe₃O₄ (Co@Fe₃O₄) nanozymes possessed stronger peroxidase activity and a 100-fold higher affinity to H₂O₂ than the Fe₃O₄ nanozymes. The lysosome localization properties of Co@Fe₃O₄ enable Co@Fe₃O₄ to catalyze the decomposition of H₂O₂ at ultralow doses for the generation of ROS bursts to effectively kill human renal tumor cells both in vitro and in vivo. Moreover, our study provides the first evidence that the Co@Fe₃O₄ nanozyme is a powerful nanozyme for the generation of ROS bursts upon the addition of H₂O₂ at ultralow doses, presenting a potential novel avenue for tumor nanozyme catalytic therapy.

Cobalt dopant in Fe₃O₄ nanozymes improved their binding affinity to H₂O₂ and enhanced the tumor catalytic therapy efficacy.