One-pot synthesis of highly monodispersed ferrite nanocrystals: surface characterization and magnetic properties

NIR-II light powered hydrogel nanomotor for intravesical instillation with enhanced bladder cancer therapy

Intravesical instillation is the common therapeutic strategy for bladder cancer. Besides chemo drugs, nanoparticles are used as intravesical instillation reagents, offering appealing therapeutic approaches for bladder cancer treatment. Metal oxide nanoparticle based chemodynamic therapy (CDT) converts tumor intracellular hydrogen peroxide to ROS with cancer cell-specific toxicity, which makes it a promising approach for the intravesical instillation of bladder cancer. However, the limited penetration of nanoparticle based therapeutic agents into the mucosa layer of the bladder wall poses a great challenge for the clinical application of CDT in intravesical instillation. Herein, we developed a 1064 nm NIR-II light driven hydrogel nanomotor for the CDT for bladder cancer via intravesical instillation. The hydrogel nanomotor was synthesized via microfluidics, wrapped with a lipid bilayer, and encapsulates CuO2 nanoparticles as a CDT reagent and core-shell structured Fe3O4@Cu9S8 nanoparticles as a fuel reagent with asymmetric distribution in the nanomotor (LipGel-NM). An NIR-II light irradiation of 1064 nm drives the active motion of LipGel-NMs, thus facilitating their distribution in the bladder and deep penetration into the mucosa layer of the bladder wall. After FA-mediated endocytosis in bladder cancer cells, CuO2 is released from LipGel-NMs due to the acidic intracellular environment for CDT. The NIR-II light powered active motion of LipGel-NMs effectively enhances CDT, providing a promising strategy for bladder cancer therapy.

Separation of mercuric ions using 2-thienylbenzimidazole/cucurbit[7]uril/iron-oxide nanoparticles by pH control

2-Thienylbenzimidazole (TBI)/cucurbit[7]uril (CB7) host-guest complex was used as a motif to significantly improve the turnover of γ-Fe₃O₄ magnetic nanoparticles for potential application in the separation of toxic mercuric ions in polluted water samples. The mechanism of restoring the original solid materials is based on applying the pH-controlled preferential binding of the CB7 host to the TBI guest. The analytical application of this concept has not been realized in the literature. The pH-controlled stimuli-responsive abilities were confirmed in aqueous solution by the three-order of magnitudes higher stability constant of the protonated TBIH⁺/CB7 complex (e.g., K = 4.8 × 10⁸ M^-1) when compared to neutral TBI/CB7 complex (e.g., K = 2.4 × 10⁵ M^-1), also manifested in an increase in pK_a values by ~ 3.3 units in the ground state. The supramolecular interaction and adsorption on iron oxide nanoparticles (NPs) were also spectroscopically confirmed in the solid state. The excited-state lifetime values of TBI/CB7NPs increased upon lowering the pH values (e.g., from 0.6 to 1.3 ns) with a concomitant blue shift of ~ 25 nm because of polarity effects. The time-resolved photoluminescent behaviors of the final solids in the presence of CB7 ensured pH-driven reusable systems for capturing toxic mercuric ions. The study offers a unique approach for the controllable separation of mercury ions using an external magnet and in response to pH through preferential binding of the host to guest molecules on the top of magnetic surfaces.

Oleic acid/oleylamine ligand pair: a versatile combination in the synthesis of colloidal nanoparticles

A variety of colloidal chemical approaches has been developed in the last few decades for the controlled synthesis of nanostructured materials in either water or organic solvents. Besides the precursors, the solvents, reducing agents, and the choice of surfactants are crucial for tuning the composition, morphology and other properties of the resulting nanoparticles. The ligands employed include thiols, amines, carboxylic acids, phosphines and phosphine oxides. Generally, adding a single ligand to the reaction mixture is not always adequate to yield the desired features. In this review, we discuss in detail the role of the oleic acid/oleylamine ligand pair in the chemical synthesis of nanoparticles. The combined use of these ligands belonging to two different categories of molecules aims to control the size and shape of nanoparticles and prevent their aggregation, not only during their synthesis but also after their dispersion in a carrier solvent. We show how the different binding strengths of these two molecules and their distinct binding modes on specific facets affect the reaction kinetics toward the production of nanostructures with tailored characteristics. Additional functions, such as the reducing function, are also noted, especially for oleylamine. Sometimes, the carboxylic acid will react with the alkylamine to form an acid-base complex, which may serve as a binary capping agent and reductant; however, its reducing capacity may range from lower to much lower than that of oleylamine. The types of nanoparticles synthesized in the simultaneous presence of oleic acid and oleylamine and discussed herein include metal oxides, metal chalcogenides, metals, bimetallic structures, perovskites, upconversion particles and rare earth-based materials. Diverse morphologies, ranging from spherical nanoparticles to anisotropic, core-shell and hetero-structured configurations are presented. Finally, the relation between tuning the resulting surface and volume nanoparticle properties and the relevant applications is highlighted.

Mismatched ligand density enables ordered assembly of mixed-dimensional, cross-species materials

The ordered coassembly of mixed-dimensional species-such as zero-dimensional (0D) nanocrystals and 2D microscale nanosheets-is commonly deemed impracticable, as phase separation almost invariably occurs. Here, by manipulating the ligand grafting density, we achieve ordered coassembly of 0D nanocrystals and 2D nanosheets under standard solvent evaporation conditions, resulting in macroscopic, freestanding hybrid-dimensional superlattices with both out-of-plane and in-plane order. The key to suppressing the notorious phase separation lies in hydrophobizing nanosheets with molecular ligands identical to those of nanocrystals but having substantially lower grafting density. The mismatched ligand density endows the two mixed-dimensional components with a molecular recognition-like capability, driving the spontaneous organization of densely capped nanocrystals at the interlayers of sparsely grafted nanosheets. Theoretical calculations reveal that the intercalation of nanocrystals can substantially reduce the short-range repulsions of ligand-grafted nanosheets and is therefore energetically favorable, while subsequent ligand-ligand van der Waals attractions induce the in-plane order and kinetically stabilize the laminate superlattice structure.

Rapid hot-injection as a tool for control of magnetic nanoparticle size and morphology

The rapid hot-injection (HI) technique was employed to synthesize magnetic nanoparticles with well-defined morphology (octahedrons, cubes, and star-like). It was shown that the proposed synthetic approach could be an alternative for the heat-up and flow hot-injection routes. Instant injection of the precursor to the hot reaction mixture (solvent(s) and additives) at high temperatures promotes fast nucleation and particle directional growth towards specific morphologies. We state that the use of saturated hydrocarbon namely hexadecane (sHD) as a new co-solvent affects the activity coefficient of monomers, forces shape-controllable growth, and allows downsizing of particles. We have shown that the rapid hot-injection route can be extended for other ferrites as well (ZnFe₂O₄, CoFe₂O₄, NiFe₂O_4, and MnFe₂O₄) which has not been done previously through the HI process before.

Rapid hot-injection can be used for precise control of magnetic particle shape.

Ternary CuZnS Nanocrystals: Synthesis, Characterization, and Interfacial Application in Perovskite Solar Cells

Ternary CuZnS nanocrystals (NCs) are synthesized via a facile, scalable, noninjection method at low temperatures for the first time, wherein sodium ascorbate plays the dual roles of reducing agent and capping ligand in the preparation process. These NCs can be dispersed well in a polar solvent like dimethyl sulfoxide, and the average size is ∼4 nm as measured by transmission electron microscopy. The results of X-ray diffraction and X-ray photoelectron spectroscopy indicate that the crystal structure of CuZnS NCs displays covellite CuS-like structure and the Zn element partly occupies the Cu position. Also, the crystal structure of CuZnS NCs is completely converted from a covellite CuS structure into a digenite Cu₉S₅ structure when the NCs are treated above 350 °C. Moreover, CuZnS NCs demonstrate favorable hole transport properties. When it is employed in MAPbI₃-based perovskite solar cells as a hole transport layer, a peak power conversion efficiency of 18.3% is achieved. Simultaneously, the devices based on CuZnS exhibit a remarkably reduced J-V hysteresis. The results indicate that CuZnS is a promising hole transport layer for enhancing perovskite solar cell performance and presents great potential for optoelectronic applications, as well.

The synthesis of a monodisperse quaternary ferrite (FeCoCrO4) from the hot injection thermolysis of the single source precursor [CrCoFeO(O2CtBu)6(HO2CtBu)3]

Monodisperse cobalt chromium ferrite (FeCoCrO₄) nanoparticles have been synthesised using the trimetallic pivalate cluster [CrCoFeO(O₂C^tBu)₆(HO₂C^tBu)₃]. The precursor was thermolysed in oleylamine and oleic acid, with diphenyl ether as the solvent at 260 °C. The effect of time and the concentration of the precursor on the stoichiometry of the phase formed and/or the morphology of the nanoparticles was studied. The reaction time was investigated by withdrawing aliquots at different times. No products were formed after 5 minutes and aliquots withdrawn at reaction times of less than 1 hour contain traces of iron oxide (Fe₂O₃); only cubic cobalt chromium ferrite (FeCoCrO₄) was obtained after one hour. Transmission Electron Microscopy (TEM) showed that more monodisperse spherical ferrite nanoparticles (4.0 ± 0.4 nm) were obtained at higher precursor concentrations. Magnetic measurements revealed that all the ferrite particles are superparamagnetic at room temperature but showed large hysteresis at low temperature. The nanoparticles were characterised by Powder X-Ray Diffraction (p-XRD) and Transmission Electron Microscopy (TEM). A Superconducting Quantum Interference Device (SQUID) was used to analyse the magnetic properties of the nanoparticles.

Magnetite nanocluster and paclitaxel-loaded charge-switchable nanohybrids for MR imaging and chemotherapy

A charge-switchable nanohybrid system that triggered by the low pH value of tumor microenvironment has been created for enhancing MR imaging sensitivity and chemotherapy efficiency.

Cit/CuS@Fe3O4-based and enzyme-responsive magnetic nanoparticles for tumor chemotherapy, photothermal, and photodynamic therapy

Safe and efficient drug delivery in a controllable fashion, especially remote and repeatable switch of on-demand drug release, is the subject of widespread attention. A kind of magnetic nanoparticles (DOX-Cit/CuS@Fe₃O₄-NPs) simultaneously consisted of Cit/CuS@Fe₃O₄ and doxorubicin (DOX) was presented. The drug release from DOX-Cit/CuS@Fe₃O₄-NPs could be successfully triggered by the presence of gelatinase, showing great promise for tumor-targeted drug release through an enzymatic degradation mechanism. Compared with free DOX, DOX-Cit/CuS@Fe₃O₄-NPs could not only specially deliver Cit/CuS@Fe₃O₄ and DOX into MCF-7 cells, but also could greatly improve the quantity of ROS produced in MCF-7 cells under of 980 nm laser irradiation. DOX-Cit/CuS@Fe₃O₄-NPs also had highly selective accumulation at tumor tissue of S₁₈₀ tumor-bearing mice, which were along with a magnet near the tumor site. Furthermore, when combined with NIR laser irridation, DOX-Cit/CuS@Fe₃O₄-NPs showed a higher antitumor efficacy than the individual therapies in vitro and in vivo. This study showed that DOX-Cit/CuS@Fe₃O₄-NPs could be used as a platform for tumor chemotherapy, photothermal and photodynamic therapy.

A facile strategy for synthesis of spinel ferrite nano-granules and their potential applications

A number of spinel ferrite nano-granules were synthesized in DMF through a calcination process under air.

Tuning the properties of cobalt ferrite: a road towards diverse applications

Cobalt ferrite nanostructures have been established to be promising material for future aspects.

Simultaneous effects of surface spins: rarely large coercivity, high remanence magnetization and jumps in the hysteresis loops observed in CoFe2O4 nanoparticles

Well-dispersed uniform cobalt ferrite nanoparticles were synthesized by thermal decomposition of a metal-organic salt in organic solvent with a high boiling point. Some of the nanoparticles were diluted in a SiO2 matrix and then the undiluted and diluted samples were characterized and their magnetic behavior explored. The undiluted and diluted samples exhibited maximum coercivity Hc of 23,817 and 15,056 Oe at 10 K, respectively, which are the highest values reported to date, and the corresponding ratios of remanence (Mr) to saturation (Ms) magnetization (Mr/Ms) were as high as 0.85 and 0.76, respectively. Interestingly, the magnetic properties of the samples changed at 200 K, which was observed in magnetic hysteresis M(H) loops and zero-field cooling curves as well as the temperature dependence of Hc, Mr/Ms, anisotropy, dipolar field, and the magnetic grain size. Below 200 K, both samples have large effective anisotropy, which arises from the surface spins, resulting in large Hc and Mr/Ms. Above 200 K, the effective anisotropy decreases because there is no contribution from surface spins, while the dipolar interaction increases, resulting in small Hc and Mr/Ms. Our results indicate that strong anisotropy and weak dipolar interaction tend to increase Hc and Mr/Ms, and also clarify that the jumps around H = 0 in M(H) loops can be attributed to the reorientation of surface spins. This work exposes the underlying mechanism in nanoscale magnetic systems, which should lead to improved magnetic performance.

Solvothermal synthesis of MnFe2O4 colloidal nanocrystal assemblies and their magnetic and electrocatalytic properties

Submicrometer MnFe₂O₄ colloidal nanocrystal assemblies (CNAs) have been synthesized controllably by using a solvothermal method through simply adjusting synthetic reagents.

A simple route to CoFe2O4 nanoparticles with shape and size control and their tunable peroxidase-like activity

A new precursor-mediated growth of monodisperse magnetic CoFe₂O₄ NPs with controlled size and shape which exhibit size and shape dependent peroxidase like activity towards TMB in the presence of H₂O₂.

Facile synthesis of ZnFe2O4 nanoparticles with tunable magnetic and sensing properties

Nanoparticles (NPs) and colloidal nanocrystal clusters (CNCs) of ZnFe2O4 were synthesized by using a solvothermal method in a controlled manner through simply adjusting the solvents. When a glycerol/water mixture was used as the solvent, ZnFe2O4 NPs were obtained. However, using ethylene glycol solvent yielded well-dispersed ZnFe2O4 CNCs. X-ray diffraction (XRD) and transmission electron microscopy (TEM) data confirmed that the ZnFe2O4 NPs were a single crystalline phase with tunable sizes ranging from 12 to 20 nm, while the ZnFe2O4 CNCs of submicrometer size consisted of single-crystalline nanosheets. Magnetic measurement results showed that the ZnFe2O4 NPs were ferromagnetic with a very small hysteresis loop at room temperature. However, CNCs displayed a superparamagnetic behavior due to preferred orientations of the nanosheets. Electrochemical sensing properties showed that both the size of the NPs and the structure of the CNCs had a great influence on their electrochemical properties in the reduction of H2O2. Based on the experimental results, the formation mechanisms of both the ZnFe2O4 CNCs and NPs as well as their structure-property relationship were discussed.

Sub-10 nm Fe3O4@Cu(2-x)S core-shell nanoparticles for dual-modal imaging and photothermal therapy

Photothermal nanomaterials have recently attracted significant research interest due to their potential applications in biological imaging and therapeutics. However, the development of small-sized photothermal nanomaterials with high thermal stability remains a formidable challenge. Here, we report the rational design and synthesis of ultrasmall (<10 nm) Fe3O4@Cu2-xS core-shell nanoparticles, which offer both high photothermal stability and superparamagnetic properties. Specifically, these core-shell nanoparticles have proven effective as probes for T2-weighted magnetic resonance imaging and infrared thermal imaging because of their strong absorption at the near-infrared region centered around 960 nm. Importantly, the photothermal effect of the nanoparticles can be precisely controlled by varying the Cu content in the core-shell structure. Furthermore, we demonstrate in vitro and in vivo photothermal ablation of cancer cells using these multifunctional nanoparticles. The results should provide improved understanding of synergistic effect resulting from the integration of magnetism with photothermal phenomenon, important for developing multimode nanoparticle probes for biomedical applications.