An ultra-small zinc ferrite nanoprobe, a preparation method and application thereof

Abstract

This invention belongs to the field of nanomaterial preparation and biomedical imaging technology, specifically relating to an ultrasmall zinc ferrite nanoprobe, its preparation method, and its application. The ultrasmall zinc ferrite nanoprobe contains zinc ferrite nanoparticles and zwitterionic molecules, with the zwitterionic molecules coordinated to the surface of the zinc ferrite nanoparticles via a catechol structure. This invention obtains the ultrasmall zinc ferrite nanoprobe by thermally decomposing iron-containing and zinc-containing compounds, followed by modification with zwitterionic molecules. The ultrasmall zinc ferrite nanoprobe has a particle size of less than 5 nm, exhibits high resistance to protein adsorption, high stability, and water solubility, with a transverse / longitudinal relaxation ratio as low as 1.09. It achieves a renal clearance efficiency of 87.25% within 1 hour, with no significant liver retention, and can be applied in high-sensitivity magnetic resonance imaging for kidney diseases.

Description

Technical Field

[0001] This invention belongs to the field of nanomaterial preparation and biomedical imaging industry, specifically relating to an ultra-small zinc ferrite nanoprobe, its preparation method and application. Background Technology

[0002] Magnetic resonance imaging (MRI) possesses unique advantages such as being non-invasive, free of ionizing radiation, offering high soft tissue resolution, and providing multi-parameter, multi-planar imaging. It is one of the most commonly used medical imaging techniques in clinical practice, playing a crucial role in disease diagnosis and treatment evaluation. Currently, over 30% of clinical MRI examinations require contrast-enhanced MRI (CE-MRI), primarily using gadolinium (Gd)-based small molecule complexes. While Gd-based small molecule complexes exhibit good relaxation properties and imaging sensitivity, their use has gradually revealed several problems: some Gd-based small molecule complexes dissociate in vivo; Gd-based small molecule complexes are mainly cleared by the kidneys, and in patients with renal insufficiency, their excretion is impaired, further increasing the risk of dissociation. Free Gd ions can easily induce serious adverse reactions such as renal systemic fibrosis, limiting their further application in CE-MRI.

[0003] Iron oxide nanoparticles possess advantages such as high safety, well-defined structure and composition, tunable particle size, and ease of surface modification, making them the most promising alternative to Gd-based small molecule complexes for CE-MRI contrast agents. Since the 1990s, various iron oxide nanoparticles, such as Ferumoxides and Ferucarbotran, have been used in clinical trials and research, but have gradually been phased out due to limitations in preparation processes and imaging performance. With the maturation of preparation processes and performance improvements, polydextrose sorbitol carboxymethyl ether-modified iron oxide nanoparticles (Ferumoxytol) were approved by the FDA in 2025 for CE-MRI evaluation of brain tumor patients. Simultaneously, several novel iron oxide nanoparticles have entered preclinical (Ganlixian) and clinical trials for CE-MRI (Magnexian (CXHL2500439)). However, existing iron oxide magnetic resonance contrast agents have two main problems: First, the core particle size of iron oxide nanoparticles is relatively large, and they easily adsorb proteins after entering the bloodstream, leading to an increase in hydraulic particle size that exceeds the pore size of the glomerular filtration membrane (6-8 nm). This makes renal clearance difficult, resulting in large-scale accumulation and long-term retention in the liver and spleen, leading to potential safety risks such as iron overload and ferroptosis. Furthermore, the retention of iron oxide nanoparticles causes long-term low signal intensity in the liver and spleen, affecting repeated short-term CE-MRI examinations. Second, the low renal accumulation and clearance efficiency of iron oxide nanoparticles limits their application in the diagnosis and assessment of kidney diseases.

[0004] Zwitterionic molecules are a class of molecules that contain both cation and anion groups but are electrically neutral overall. Zwitterionic modification of nanoparticles can form a dense hydration layer on their surface, effectively preventing protein adsorption and hydrodynamic particle size increase. Therefore, developing sub-5 nm ultrasmall iron oxide probes modified with zwitterionic molecules holds promise for achieving efficient renal clearance and solving the current problems faced by iron oxide nanoparticles in CE-MRI applications. To this end, in 2017, He W. et al. developed a sub-5 nm zwitterionic iron oxide nanoprobe (PNAS. 2017, 114, 2325), achieving efficient renal clearance and CE-MRI imaging. However, this iron oxide nanoprobe has a low longitudinal relaxation rate, and the preparation process requires pretreatment with 2-(2-(2-methoxyethoxy)ethoxy)acetic acid before zwitterionic modification, which is complex and limits its further application.

[0005] Metal ion doping is an important method for modulating the properties of iron oxide nanoparticles, significantly affecting their crystal structure and the state of exposed surface atoms, thereby influencing the efficiency of surface ligand functionalization and the imaging performance of the probe. Currently, metal doping is mainly used to modulate the imaging performance of non-renal scavengable iron oxide nanoparticles (Advanced Materials 2024, 36, 2401538). In 2024, Zhou T. et al. reported a zwitterionic-modified sub-5 nm manganese ferrite nanoprobe (Advanced Healthcare Materials 2024, 13, 2304577), whose longitudinal relaxation rate ( r 1) is 12.52 mM -1 ·s -1 The probe has a hydrodynamic size of 6.43 nm and a transverse / longitudinal relaxation ratio of 2.04 under a 3.0 T magnetic field. It can be partially cleared by the kidneys, solving the problems of low imaging sensitivity and difficult ligand exchange. However, due to the targeting effect of manganese ions on liver parenchymal cells and the probe's high transverse relaxation rate (25.51 mM), it is not suitable for ligand exchange. -1 ·s -1 The high ratio of manganese ions to calcium ions (2.04) and their transverse / longitudinal relaxation rate resulted in the probe's retention in the liver and the generation of significant T2-weighted imaging phenomena. Simultaneously, the presence of manganese ions as calcium ion analogs, which can be voltage-gated into hypermetabolic cells, led to the probe's prolonged retention in the renal medulla. Therefore, developing sub-5 nm iron oxide nanoprobes with low protein adsorption in blood, high imaging performance, and efficient renal clearance is of great significance, but challenges remain. Summary of the Invention

[0006] In view of this, the purpose of this invention is to provide an ultrasmall zinc ferrite nanoprobe, its preparation method, and its application. In the ultrasmall zinc ferrite nanoprobe, the zinc-doped iron oxide crystal nucleus and the surface modification of the zwitterionic molecular ligand form a synergistic effect, giving the probe a high longitudinal relaxation rate, a low lateral / longitudinal relaxation rate ratio, and high renal clearance efficiency. Using the ultrasmall zinc ferrite nanoprobe prepared by this invention as a magnetic resonance imaging contrast agent, it exhibits high imaging contrast, excellent sensitivity, and high biosafety, being rapidly cleared by the kidneys.

[0007] This invention provides an ultra-small zinc ferrite nanoprobe containing zinc ferrite nanoparticles and zwitterionic molecules, wherein the molar ratio of iron to zinc is 0.5 to 10:1, and the zwitterionic molecules are modified on the surface of zinc ferrite nanoparticles by coordination with metal elements through a catechol structure. The ultrasmall zinc ferrite nanoprobe also possesses the following properties: (1) The crystal core size is less than 5 nm; (2) Hydrodynamic size is less than 8 nm; (3) Under a magnetic field of 3.0 T, the longitudinal relaxation rate is greater than 2 mM. -1 ·s -1 The ratio of lateral to longitudinal relaxation rate is less than 1.5.

[0008] Preferably, the zwitterionic molecule includes 3-((3,4-dihydroxyphenylethyl)dimethylammonium)propane-1-sulfonate, 3-((3,4-dihydroxyphenylethyl)dimethylammonium)propane-1-carboxylate, 3-hydroxy-L-tyrosine, or 3-((3-((2-amino-3-(3,4-dihydroxyphenyl)propionyl)oxy)propyl)dimethylammonium)propane-1-sulfonate).

[0009] This invention also provides a method for preparing the ultrasmall zinc ferrite nanoprobe described in the above technical solution, comprising the following steps: (1) Iron precursor, zinc precursor, ligand and organic solvent were mixed according to stoichiometric ratio and thermally decomposed under inert gas protection to prepare oil-soluble ultra-small zinc ferrite nanoparticles. (2) The oil-soluble ultra-small zinc ferrite nanoparticles described in step (1) are dispersed in an organic solvent, and the zwitterionic molecules and alkali metal salts are dispersed in a mixed solvent of water and acetone. Under the protection of an inert gas, the two solutions are mixed and reacted to allow the ligands on the surface of the oil-soluble ultra-small zinc ferrite nanoparticles to exchange ligands with the zwitterionic molecules, thereby obtaining ultra-small zinc ferrite nanoprobes.

[0010] Preferably, the iron precursor includes one or more of ferric nitrate, ferric sulfate, ferric acetate, ferric chloride, ferric stearate, ferric pentacarbonyl, ferric acetylacetone, ferric erucic acid, and ferric oleate.

[0011] Preferably, the zinc precursor includes one or more of zinc nitrate, zinc sulfate, zinc acetate, zinc chloride, zinc acetylacetonate, and basic zinc carbonate.

[0012] Preferably, the molar ratio of the iron precursor to the zinc precursor is 1:0.1~3.

[0013] Preferably, the temperature of the thermal decomposition reaction is 220~320 ℃.

[0014] Preferably, the temperature of the thermal decomposition reaction is maintained for 5 minutes to 2 hours.

[0015] Preferably, the mass ratio of the oil-soluble ultrasmall zinc ferrite nanoparticles to the zwitterionic molecules is 0.1 to 3:1; the organic solvent for dispersing the oil-soluble ultrasmall zinc ferrite nanoparticles includes dichloromethane, chloroform, cyclohexane, or n-hexane.

[0016] This invention also provides the application of the ultra-small zinc ferrite nanoprobes described in the above technical solutions or the ultra-small zinc ferrite nanoprobes prepared by the above methods as magnetic resonance imaging contrast agents.

[0017] Compared with the prior art, the present invention has the following beneficial effects: This invention provides an ultrasmall zinc ferrite nanoprobe. The zinc-doped iron oxide nucleus and the surface modification with zwitterionic molecular ligands form a synergistic effect, resulting in a probe with high longitudinal relaxation rate, low lateral / longitudinal relaxation rate ratio, and high renal clearance efficiency. Its hydrodynamic size is less than 8 nm, with the ultrasmall zinc ferrite nanoprobe of Example 1 exhibiting a longitudinal relaxation rate of 2.83 mM. -1 ·s -1The ratio of transverse relaxation rate to longitudinal relaxation rate is 1.09. Furthermore, the zinc and iron elements in the ultrasmall zinc ferrite nanoprobe are both abundant metals in the human body (zinc: 2 g / 70 kg body weight, iron: 5 g / 70 kg body weight), far exceeding the content of manganese (manganese: 16 mg / 70 kg body weight). Zinc doping enhances ligand exchange yield while ensuring the high safety of the nanoprobe. After intravenous injection, the hydrophilic properties of zwitterionic molecules effectively reduce plasma protein adsorption on the probe surface, promoting renal clearance; the renal clearance rate reaches 87.25% within 1 hour. Compared with currently used Ferumoxytol and zwitterionic-modified manganese ferrite nanoprobes, the core advantage lies in low hepatic retention. The benefits include: from an imaging perspective, the liver signal does not decrease for a prolonged period after intravenous injection of the ultrasmall zinc ferrite nanoprobe, effectively adapting to applications requiring short-term repetitive CE-MRI examinations; from a safety perspective, the ultrasmall zinc ferrite nanoprobe effectively avoids long-term liver accumulation, preventing iron overload and potential toxicity.

[0018] This invention provides an ultra-small zinc ferrite nanoprobe. The zinc-doped iron oxide crystal nucleus and the surface modification with zwitterionic molecular ligands create a synergistic effect, resulting in a probe with high longitudinal relaxation rate, low transverse / longitudinal relaxation rate ratio, and high renal clearance efficiency. Furthermore, the short-term renal accumulation and clearance process enhances its sensitivity for kidney diagnosis, enabling magnetic resonance imaging diagnosis and staging of acute kidney injury. Simultaneously, it does not remain in the kidney after imaging, avoiding the problem of gadolinium-based contrast agents easily remaining and accumulating in patients with kidney injury, thus increasing the risk of serious adverse reactions such as renal systemic fibrosis.

[0019] This invention provides a method for preparing ultrasmall zinc ferrite nanoprobes. Zinc doping not only alters imaging performance but also improves ligand exchange efficiency. Compared to previously reported methods, the preparation method provided by this invention offers advantages such as simplicity, efficiency, and ease of large-scale synthesis. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 This is a schematic diagram of the structure of the ultra-small zinc ferrite nanoprobe of the present invention; Figure 2 Transmission electron microscopy images of the ultra-small zinc ferrite nanoprobes in Examples 1-3; Figure 3The figures show the hydrodynamic diameters of the zinc ferrite nanoprobes in Examples 1-3 and Comparative Examples 1-2. Figure 4 The infrared spectra of oleic acid, oil-soluble ultrasmall zinc ferrite nanoparticles, 3-((3,4-dihydroxyphenylethyl)dimethylammonium)propane-1-sulfonate, and ultrasmall zinc ferrite nanoprobes in Example 1 are shown below. Figure 5 The relaxation rate diagrams are for the ultra-small zinc ferrite nanoprobes in Examples 1-3; Figure 6 This is an agarose gel electrophoresis image of the ultra-small zinc ferrite nanoprobe in Example 1; Figure 7 The image shows the T1-weighted magnetic resonance imaging of the coronal region of the abdomen of a normal SD rat using the ultra-small zinc ferrite nanoprobe in Example 1, with Ferumoxytol and ultra-small manganese ferrite nanoprobe (Comparative Example 4) as controls. Figure 8 The iron content in the urine of normal SD rats after 1 hour was measured using the ultra-small zinc ferrite nanoprobe in Example 1, with physiological saline as a control. Figure 9 The image shows the T1-weighted magnetic resonance imaging of the coronal region of the ultra-small zinc ferrite nanoprobe in the kidney-injured SD rats in Example 1, with gadopentetate dimeglumine (Gd-DTPA) as a control. Figure 10 This is a comparison chart of the yield of the ultra-small zinc ferrite nanoprobe in Example 1 and the ultra-small ferrite nanoprobe in Comparative Example 3. Detailed Implementation

[0022] This invention provides an ultra-small zinc ferrite nanoprobe containing zinc ferrite nanoparticles and zwitterionic molecules, wherein the molar ratio of iron to zinc is 0.5 to 10:1, and the zwitterionic molecules are modified on the surface of zinc ferrite nanoparticles by coordination with metal elements through a catechol structure. The ultrasmall zinc ferrite nanoprobe also possesses the following properties: (1) The crystal core size is less than 5 nm; (2) Hydrodynamic size is less than 8 nm; (3) Under a magnetic field of 3.0 T, the longitudinal relaxation rate is greater than 2 mM. -1 ·s -1 The ratio of lateral to longitudinal relaxation rate is less than 1.5.

[0023] In this invention, the hydrodynamic size of the ultrasmall zinc ferrite nanoprobe is preferably less than 6 nm.

[0024] In this invention, the zwitterionic molecule preferably includes 3-((3,4-dihydroxyphenylethyl)dimethylammonium)propane-1-sulfonate, 3-((3,4-dihydroxyphenylethyl)dimethylammonium)propane-1-carboxylate, 3-hydroxy-L-tyrosine, or 3-((3-((2-amino-3-(3,4-dihydroxyphenyl)propionyl)oxy)propyl)dimethylammonium)propane-1-sulfonate).

[0025] In this invention, the preferred iron content in the ultra-small zinc ferrite nanoprobe is 4.81%, and the preferred Zn content is 4.67%. The preferred molar ratio of iron to zinc in the ultra-small zinc ferrite nanoprobe is 1.2:1.

[0026] This invention provides a method for preparing the ultrasmall zinc ferrite nanoprobe described in the above technical solution, comprising the following steps: (1) Iron precursor, zinc precursor, ligand and organic solvent were mixed according to stoichiometric ratio and thermally decomposed under inert gas protection to prepare oil-soluble ultra-small zinc ferrite nanoparticles. (2) The oil-soluble ultra-small zinc ferrite nanoparticles described in step (1) are dispersed in an organic solvent, and the zwitterionic molecules and alkali metal salts are dispersed in a mixed solvent of water and acetone. Under the protection of an inert gas, the two solutions are mixed and reacted to allow the ligands on the surface of the oil-soluble ultra-small zinc ferrite nanoparticles to exchange ligands with the zwitterionic molecules, thereby obtaining ultra-small zinc ferrite nanoprobes.

[0027] Unless otherwise specified, all materials and equipment used in this invention are commercially available products in the field.

[0028] This invention involves mixing an iron precursor, a zinc precursor, a ligand, and an organic solvent in stoichiometric proportions and carrying out a thermal decomposition reaction under inert gas protection to prepare oil-soluble ultra-small zinc ferrite nanoparticles.

[0029] In this invention, the iron precursor preferably includes one or more of ferric nitrate, ferric sulfate, ferric acetate, ferric chloride, ferric stearate, ferric pentacarbonyl, ferric acetylacetone, ferric erucic acid, and ferric oleate; the zinc precursor preferably includes one or more of zinc nitrate, zinc sulfate, zinc acetate, zinc chloride, zinc acetylacetone, and basic zinc carbonate.

[0030] In this invention, the preferred molar ratio of the iron precursor to the zinc precursor is 1:0.1 to 3, specifically 1:1, 3:1 or 1:3.

[0031] In this invention, the ligand preferably comprises oleic acid and oleylamine, and the molar ratio of oleic acid and oleylamine is preferably 1:1; the molar ratio of the total amount of the iron precursor and zinc precursor to the total amount of the ligand is preferably 1:3. The organic solvent preferably comprises diphenyl ether. When the iron precursor, zinc precursor, ligand and organic solvent are mixed, 1,2-hexadecanediol is preferably added; the molar ratio of oleic acid, oleylamine and 1,2-hexadecanediol is preferably 1:1:2.

[0032] In this invention, the temperature of the thermal decomposition reaction is preferably 220~320 ℃, specifically 230 ℃, and the holding time is preferably 5 minutes to 2 hours, specifically 10 minutes.

[0033] After obtaining the oil-soluble ultrasmall zinc ferrite nanoparticles, the present invention disperses the oil-soluble ultrasmall zinc ferrite nanoparticles obtained in step (1) in an organic solvent, and disperses the zwitterionic molecules and alkali metal salts in a mixed solvent of water and acetone. Under the protection of an inert gas, the two solutions are mixed and reacted to allow the ligands on the surface of the oil-soluble ultrasmall zinc ferrite nanoparticles to exchange ligands with the zwitterionic molecules, thereby obtaining ultrasmall zinc ferrite nanoprobes.

[0034] In this invention, the mass ratio of the oil-soluble ultrasmall zinc ferrite nanoparticles to the zwitterionic molecules is preferably 0.1 to 3:1, specifically 1.4:1; the organic solvent for dispersing the oil-soluble ultrasmall zinc ferrite nanoparticles includes dichloromethane, trichloromethane, cyclohexane, or n-hexane. The alkali metal salt preferably includes sodium bicarbonate, and the volume ratio of water to acetone in the mixed solvent of water and acetone is preferably 1:1.

[0035] In this invention, the preferred temperature for the two solutions mixing reaction (ligand exchange) is 37 °C, and the preferred time is 4 hours.

[0036] This invention provides the application of the ultra-small zinc ferrite nanoprobe described in the above technical solution as a contrast agent for magnetic resonance imaging (MRI).

[0037] In clinical practice, many diseases (such as tumors, inflammation, and vascular lesions) require multiple enhanced MRI examinations at different stages of the disease to dynamically assess disease progression, treatment effectiveness, and prognosis. However, traditional contrast agents cannot meet the clinical needs of such repeated examinations: gadolinium-based contrast agents have clear contraindications for patients with impaired renal function and cannot be used for multiple enhanced imaging in such patients; traditional iron-based contrast agents are difficult to be effectively cleared by the kidneys, and repeated use can easily lead to accumulation in the body, increasing safety risks. This invention, through precise control of nanoparticle size, elemental doping, and optimized surface modification strategies, represents a core approach to addressing the shortcomings of traditional iron oxide nanoparticle technology and enhancing the overall performance of iron-based contrast agents. By controlling the iron-based nanoparticles to ultra-small sizes, their specific surface area, tissue penetration, and in vivo metabolic rate are significantly improved, enabling rapid renal clearance and preventing accumulation in the body. The formation of composite ferrites through zinc doping allows for precise control of the nanoparticle crystal structure and magnetic properties, improving relaxation efficiency. Furthermore, the surface modification of the ultra-small composite ferrite nanoparticles with suitable zwitterionic ligands further optimizes their biocompatibility and in vivo metabolic characteristics, preventing excessive clearance by the mononuclear phagocytic system while ensuring rapid excretion through the kidneys. This meets the clinical needs of multiple enhanced MRI examinations at different stages of disease progression, demonstrating significant clinical application advantages. It provides a new solution for the development of highly sensitive, safe, and high-performance iron-based magnetic resonance contrast probes, particularly suitable for the clinical imaging diagnostic needs of patients with impaired renal function, thus addressing the shortcomings of existing contrast agents.

[0038] To further illustrate the present invention, the ultra-small zinc ferrite nanoprobes, their preparation methods, and applications provided by the present invention are described in detail below with reference to the accompanying drawings, embodiments, and comparative examples. However, these descriptions should not be construed as limiting the scope of protection of the present invention.

[0039] Example 1 Preparation of ultrasmall zinc ferrite nanoprobes: Step 1: Dissolve 2 mmol of acetylacetone iron, 2 mmol of acetylacetone zinc, oleic acid (6 mmol), oleylamine (6 mmol), and 1,2-hexadecanediol (12 mmol) in diphenyl ether (20 mL) at room temperature; stir the reaction mixture at 110 °C under vacuum for 30 minutes to remove water from the reaction system; increase the temperature of the reaction system to 230 °C at a rate of 10 °C / min under stirring and argon protection, and maintain this temperature for 10 minutes; after the time is up, rapidly cool the reaction system to room temperature, purify it by centrifugation using cyclohexane and anhydrous ethanol as good and bad solvents respectively, and vacuum dry to obtain oil-soluble ultrafine zinc ferrite nanoparticles for later use.

[0040] Step 2: 3-((3,4-dihydroxyphenylethyl)dimethylammonium)propane-1-sulfonate (ZDS, 100 mg) and sodium bicarbonate (60 mg) were dissolved in a mixture of ultrapure water (20 mL) and acetone (20 mL), and the reaction was carried out under argon protection with stirring. Subsequently, a solution of chloroform (10 mL) containing oil-soluble ultrafine zinc ferrite nanoparticles (140 mg) was added to the above mixture, and the reaction was carried out at 37 °C with stirring for 4 hours. After the time was completed, the reaction solution was centrifuged at low speed to separate the layers, and the upper layer was collected. The acetone in the upper layer was removed by rotary evaporation. The remaining solution was washed three times with ultrapure water by ultrafiltration and freeze-dried to obtain ultrafine zinc ferrite nanoprobe solid powder for later use.

[0041] The performance of the ultrasmall zinc ferrite nanoprobe from Example 1 was characterized by: observing the size and morphology of the ultrasmall zinc ferrite nanoprobe using transmission electron microscopy; determining the hydrodynamic size of the nanoprobe in aqueous solution using dynamic light scattering; verifying the modification effect of zwitterionic molecules on the surface of nanoparticles using Fourier transform infrared spectroscopy; and determining the zinc and iron content in the solid powder of the ultrasmall zinc ferrite nanoprobe using inductively coupled plasma atomic emission spectrometry.

[0042] Figure 2 The results showed that, as observed by transmission electron microscopy, the ultrasmall zinc ferrite nanoprobes were nearly spherical and uniformly distributed, with no obvious aggregation. Statistical analysis of the diameters of 50 randomly selected particles revealed an average size of 2.92 ± 0.58 nm, indicating highly uniform particle size and good monodispersity.

[0043] The average hydrodynamic diameter of the sample in aqueous solution, measured by dynamic light scattering (DLS), was 3.14 ± 0.33 nm. Figure 3 The value is slightly larger than the TEM measured value, mainly due to the presence of the ZDS modification layer and hydration layer on the surface. This size is smaller than that of the glomerular filtration membrane and can be rapidly cleared by the kidneys.

[0044] Fourier transform infrared spectroscopy analysis ( Figure 4 After ligand exchange, the characteristic peak of oleic acid (OA) disappeared, and the characteristic peak of 3-((3,4-dihydroxyphenylethyl)dimethylammonium)propane-1-sulfonate appeared. This result proves that 3-((3,4-dihydroxyphenylethyl)dimethylammonium)propane-1-sulfonate has successfully replaced the oleic acid molecules on the surface of oil-soluble ultrasmall zinc ferrite nanoparticles, realizing the transformation from oil-soluble to water-soluble surface.

[0045] The metal elemental composition of the sample was analyzed by inductively coupled plasma emission spectroscopy, and the Fe mass content was found to be 4.81% and the Zn mass content was 4.67%.

[0046] The relaxation properties of the ultrasmall zinc ferrite nanoprobes obtained in Example 1 were characterized by the following steps: ultrasmall zinc ferrite nanoprobe solutions with Fe concentrations of 0, 0.1, 0.5, 1, 1.5, and 2 mM were scanned using a clinical MR scanner.

[0047] Figure 5 The results show that the T1 relaxation rate of the ultrasmall zinc ferrite nanoprobe is r 1 = 2.83 mM -1 ·s -1 T2 relaxation rate r 2 = 3.08 mM -1 ·s -1 , r 2 / r The I-value is 1.09, indicating good T1-weighted imaging contrast enhancement capability.

[0048] The anti-protein adsorption performance of the ultrasmall zinc ferrite nanoprobe obtained in Example 1 was characterized by the following steps: using 1.5% agarose gel as a carrier, electrophoresis was performed at 200 V for 10 min with 1×Tris-acetic acid buffer (pH=7.4) to separate Coomassie Brilliant Blue and ultrasmall zinc ferrite nanoprobes with / without 20% fetal bovine serum. The strips were then cut and treated with nitric acid, and the protein adsorption behavior of the nanoprobes was evaluated by inductively coupled plasma atomic emission spectrometry.

[0049] Figure 6 The agarose gel electrophoresis and inductively coupled plasma atomic emission spectrometry analysis results (① in the figure is Coomassie Brilliant Blue, ② is Coomassie Brilliant Blue + ultra-small zinc ferrite nanoprobe, ③ is Coomassie Brilliant Blue + serum, ④ is Coomassie Brilliant Blue + serum + ultra-small zinc ferrite nanoprobe) show that about 20% of the ultra-small zinc ferrite nanoprobes adsorb serum proteins, and the modification with zwitterionic molecules can effectively inhibit the adsorption of non-specific serum proteins and the formation of protein crowns.

[0050] The abdominal enhanced magnetic resonance imaging (MRI) effect of the ultrasmall zinc ferrite nanoprobe obtained in Example 1 was tested, including the following steps: The metabolic behavior of the nanoparticles was studied in rats using MRI. The ultrasmall zinc ferrite nanoprobe nanoparticles and Ferumoxytol were intravenously injected into rats (0.1 mmol Fe / kg). Subsequently, coronal T1-weighted MRI of the abdomen was performed at different time points, and the imaging results were analyzed.

[0051] Figure 7Coronal imaging results showed that the ultrasmall zinc ferrite nanoprobe exhibited significant renal enrichment and renal clearance metabolism after injection. The liver showed only transient, mild enhancement, without significant hepatic signal reduction. The kidneys showed significant enhancement within 5 minutes of injection, followed by a marked decrease in enhancement intensity. Enhancement was observed only in the renal pelvis at 1 hour post-injection, and essentially returned to pre-injection levels at 4 hours. Figure 7 Coronal imaging results from the study showed that the rat liver began to darken 5 minutes after intravenous injection of Ferumoxytol, exhibiting T2WI imaging effects. This demonstrates that Ferumoxytol is significantly enriched in the liver, and this darkening effect is more pronounced in the following 4 hours, lasting for more than 14 days. Compared to the liver, the kidneys showed T1WI imaging effects after intravenous injection of Ferumoxytol, with a duration exceeding 4 hours. These results demonstrate that the ultra-small zinc ferrite nanoprobe can be rapidly cleared by the kidneys, while Ferumoxytol shows significant retention in the liver and kidneys after intravenous injection, especially in the liver where retention can last for more than 14 days. This indicates that the ultra-small zinc ferrite nanoprobe is effectively suitable for applications requiring short-term repetitive CE-MRI examinations.

[0052] The renal clearance rate of the ultrasmall zinc ferrite nanoprobe obtained in Example 1 was determined by the following steps: The renal clearance rate of nanoparticles in rats was studied by analyzing the iron content in urine. The ultrasmall zinc ferrite nanoprobe was intravenously injected into rats (0.1 mmol Fe / kg), while the control group was injected with an equal volume of physiological saline. Subsequently, the urethra of the rats was ligated and all urine was collected. The iron content in the urine was determined by inductively coupled plasma atomic emission spectrometry.

[0053] Figure 8 The results of the iron content in rat urine 1 hour after injection of physiological saline and ultra-small zinc ferrite nanoprobe showed that the ultra-small zinc ferrite nanoprobe was metabolized and excreted via the kidney, and the renal clearance rate of the probe reached 87.25% after 1 hour.

[0054] The enhanced magnetic resonance imaging (MRI) effect of the ultrasmall zinc ferrite nanoprobe obtained in Example 1 on a cisplatin-induced kidney injury rat model was tested, including the following steps: The metabolic behavior of the nanoparticles was studied in vivo by MRI in rats. The ultrasmall zinc ferrite nanoprobe nanoparticles were intravenously injected into rats (0.1 mmol Fe / kg). Subsequently, coronal T1-weighted MRI of the abdomen was performed at different time points, and the imaging results were analyzed.

[0055] Figure 9The results showed that the ultra-small zinc ferrite nanoprobes maintained unique rapid renal clearance characteristics in renal injury models of different severities. In the mild renal injury group, rat kidneys showed significant enhancement 5 minutes after injection, cortical signal began to decline 15 minutes later, and essentially recovered to pre-injection levels within 2 hours. All renal areas were completely restored within 4 hours, with no significant retention. Even in the severe renal injury group (severely damaged glomerular filtration barrier and hemodynamic disturbances), there was no significant retention, and the renal disease recovered to pre-injection levels within 4 hours without increasing the burden on the kidneys.

[0056] In stark contrast, the clinically standard gadolinium-based contrast agent Gd-DTPA exhibited significant renal retention in a kidney injury model. In healthy SD rats, Gd-DTPA injection showed significant renal enhancement within 5 minutes, followed by a marked decrease in enhancement, returning to pre-injection levels by 4 hours. This indicates that Gd-DTPA is rapidly cleared by the kidneys in healthy SD rats. However, in the mild kidney injury group, significant renal enhancement was observed after Gd-DTPA injection, particularly in the cortex, which remained highly signal-inducing even 4 hours post-injection. In the severe kidney injury group, Gd-DTPA retention was even more pronounced, with the entire kidney showing highly signal-inducing activity 4 hours after injection, suggesting substantial retention of the contrast agent in the injured kidney and increasing the risks associated with the use of gadolinium-based contrast agents. In conclusion, compared to Gd-DTPA, the ultra-small zinc ferrite nanoprobe demonstrates higher safety and clinical applicability in MRI examinations of patients with kidney injury.

[0057] Example 2 Preparation of ultrasmall zinc ferrite nanoprobes: Iron acetylacetone (3 mmol), zinc acetylacetone (1 mmol), oleic acid (6 mmol), oleylamine (6 mmol), and 1,2-hexadecanediol (12 mmol) were dissolved in diphenyl ether (20 mL) at room temperature. The reaction mixture was stirred at 110 °C under vacuum for 30 minutes to remove water from the reaction system. Under stirring and argon protection, the temperature of the reaction system was increased to 230 °C at a rate of 10 °C / min and maintained at this temperature for 10 minutes. After the time was completed, the reaction system was rapidly cooled to room temperature, purified by centrifugation using cyclohexane and anhydrous ethanol, and vacuum dried to obtain oil-soluble ultrafine zinc ferrite nanoparticles for later use.

[0058] Step 2: 3-((3,4-dihydroxyphenylethyl)dimethylammonium)propane-1-sulfonate (ZDS, 100 mg) and sodium bicarbonate (60 mg) were dissolved in a mixture of ultrapure water (20 mL) and acetone (20 mL), and the reaction was carried out under argon protection with stirring. Subsequently, a solution of chloroform (10 mL) containing oil-soluble ultrafine zinc ferrite nanoparticles (140 mg) was added to the above mixture, and the reaction was carried out at 37 °C with stirring for 4 hours. After the time was completed, the reaction solution was centrifuged at low speed to separate the layers, and the upper layer was collected. The acetone in the upper layer was removed by rotary evaporation. The remaining solution was washed three times with ultrapure water by ultrafiltration and then freeze-dried to obtain ultrafine zinc ferrite nanoprobe solid powder for later use.

[0059] Figure 2 The results showed that, as observed by transmission electron microscopy, the ultrasmall zinc ferrite nanoprobes were nearly spherical and uniformly distributed, with no obvious aggregation. Statistical analysis of the diameters of 50 randomly selected particles revealed an average size of 1.81 ± 0.27 nm, indicating highly uniform particle size and good monodispersity.

[0060] The average hydrodynamic diameter of the sample in aqueous solution, measured by dynamic light scattering (DLS), is 2.71 ± 0.28 nm. Figure 3 The value is slightly larger than the TEM measured value, mainly due to the presence of the ZDS modification layer and hydration layer on the surface. This size is smaller than that of the glomerular filtration membrane and can be rapidly cleared by the kidneys.

[0061] The relaxation properties of the ultrasmall zinc ferrite nanoprobes obtained in Example 2 were characterized by the following steps: ultrasmall zinc ferrite nanoprobe solutions with Fe concentrations of 0, 0.1, 0.5, 1, 1.5, and 2 mM were scanned using a clinical MR scanner.

[0062] Figure 5 The results show that the T1 relaxation rate of the ultrasmall zinc ferrite nanoprobe is r 1 = 3.36 mM -1 ·s -1 T2 relaxation rate r 2 = 4.31mM -1 ·s -1 , r 2 / r The I-value is 1.28, indicating good T1-weighted imaging contrast enhancement capability.

[0063] Example 3 Preparation of ultrasmall zinc ferrite nanoprobes: Iron acetylacetone (1 mmol), zinc acetylacetone (3 mmol), oleic acid (6 mmol), oleylamine (6 mmol), and 1,2-hexadecanediol (12 mmol) were dissolved in diphenyl ether (20 mL) at room temperature. The reaction mixture was stirred at 110 °C under vacuum for 30 minutes to remove water from the reaction system. Under stirring and argon protection, the temperature of the reaction system was increased to 230 °C at a rate of 10 °C / min and maintained at this temperature for 10 minutes. After the time was completed, the reaction system was rapidly cooled to room temperature, purified by centrifugation using cyclohexane and anhydrous ethanol, and vacuum dried to obtain oil-soluble ultrafine zinc ferrite nanoparticles for later use.

[0064] Step 2: 3-((3,4-dihydroxyphenylethyl)dimethylammonium)propane-1-sulfonate (ZDS, 100 mg) and sodium bicarbonate (60 mg) were dissolved in a mixture of ultrapure water (20 mL) and acetone (20 mL), and the reaction was carried out under argon protection with stirring. Subsequently, a solution of chloroform (10 mL) containing oil-soluble ultrafine zinc ferrite nanoparticles (140 mg) was added to the above mixture, and the reaction was carried out at 37 °C with stirring for 4 hours. After the time was completed, the reaction solution was centrifuged at low speed to separate the layers, and the upper layer was collected. The acetone in the upper layer was removed by rotary evaporation. The remaining solution was washed three times with ultrapure water by ultrafiltration and then freeze-dried to obtain ultrafine zinc ferrite nanoprobe solid powder for later use.

[0065] Figure 2 The results showed that, as observed by transmission electron microscopy, the ultrasmall zinc ferrite nanoprobes were nearly spherical and uniformly distributed, with no obvious aggregation. Statistical analysis of the diameters of 50 randomly selected particles revealed an average size of 3.36 ± 0.8 nm, indicating highly uniform particle size and good monodispersity.

[0066] The average hydrodynamic diameter of the sample in aqueous solution, measured by dynamic light scattering (DLS), is 5.15 ± 0.65 nm. Figure 3 The value is slightly larger than the TEM measured value, mainly due to the presence of the ZDS modification layer and hydration layer on the surface. This size is smaller than that of the glomerular filtration membrane and can be rapidly cleared by the kidneys.

[0067] The relaxation properties of the ultrasmall zinc ferrite nanoprobes obtained in Example 3 were characterized by the following steps: ultrasmall zinc ferrite nanoprobe solutions with Fe concentrations of 0, 0.1, 0.5, 1, 1.5, and 2 mM were scanned using a clinical MR scanner.

[0068] Figure 5 The results show that the T1 relaxation rate of the ultrasmall zinc ferrite nanoprobe is r 1 = 2.01 mM-1 ·s -1 T2 relaxation rate r 2 = 2.48 mM -1 ·s -1 , r 2 / r The I value is 1.23, which shows good T1-weighted imaging contrast enhancement capability.

[0069] Comparative Example 1 The preparation method of citric acid-modified zinc ferrite nanoprobes includes the following steps: Step 1: Dissolve 2 mmol of acetylacetone iron, 2 mmol of acetylacetone zinc, oleic acid (6 mmol), oleylamine (6 mmol), and 1,2-hexadecanediol (12 mmol) in diphenyl ether (20 mL) at room temperature; stir the reaction at 110 °C under vacuum for 30 minutes to remove water from the reaction system; increase the temperature of the reaction system to 230 °C at a rate of 10 °C / min under stirring and argon protection, and maintain this temperature for 10 minutes; after the time is up, rapidly cool the reaction system to room temperature, purify it by centrifugation using cyclohexane and anhydrous ethanol, and vacuum dry to obtain oil-soluble ultrafine zinc ferrite nanoparticles for later use.

[0070] Step 2: Dissolve oil-soluble ultrasmall zinc ferrite nanoparticles (60 mg) and citric acid (130 mg) in N,N-dimethylformamide (7.5 mL) and o-dichlorobenzene (7.5 mL) at room temperature; heat and stir at 100 °C under reflux for 24 hours; after the time is up, purify by centrifugation with acetone; dissolve the product in water and freeze-dry to obtain citric acid-modified ultrasmall zinc ferrite nanoprobe solid for later use.

[0071] Comparative Example 2 Preparation of dopamine-polyethylene glycol modified zinc ferrite nanoprobes: The method for preparing oil-soluble ultrasmall zinc ferrite nanoparticles in step 1 is the same as that in step 1 of Comparative Example 1.

[0072] Step 2: Polyethylene glycol (number average molecular weight Mn of 600, 480 mg), sodium carbonate (240 mg), N-hydroxysuccinimide (48 mg), dicyclohexylcarbodiimide (72 mg), and dopamine hydrochloride (33.6 mg) were dissolved in N,N-dimethylformamide (24 mL) and chloroform (48 mL) at room temperature and stirred at room temperature for 2 hours. After the time was up, oil-soluble ultrasmall zinc ferrite nanoparticles (120 mg) were added, and the reaction was continued at room temperature with stirring for 14 hours. After the time was up, the product was purified by centrifugation using cyclohexane and fully dissolved in water. The product was washed three times with ultrapure water by ultrafiltration and freeze-dried to obtain a solid dopamine-polyethylene glycol modified ultrasmall ferrite nanoprobe for later use.

[0073] The hydrodynamic diameters of the nanometer probes in Comparative Examples 1 and 1 and 2 are as follows: Figure 3 It is evident that zwitterionic modification can significantly reduce the hydrodynamic diameter of nanoprobes compared to those modified with citric acid, dopamine-polyethylene glycol.

[0074] Comparative Example 3 Preparation of zwitterionic-modified ultrasmall ferrite nanoprobes: Ferric acetylacetone (4 mmol), oleic acid (6 mmol), oleylamine (6 mmol), and 1,2-hexadecanediol (12 mmol) were dissolved in diphenyl ether (20 mL) at room temperature. The reaction mixture was stirred at 110 °C under vacuum for 30 minutes to remove water from the reaction system. Under stirring and argon protection, the temperature of the reaction system was increased to 230 °C at a rate of 10 °C / min and maintained at this temperature for 10 minutes. After the time was completed, the reaction system was rapidly cooled to room temperature, purified by centrifugation using cyclohexane and anhydrous ethanol, and vacuum dried to obtain oil-soluble ultrafine ferrite nanoparticles for later use.

[0075] Step 2: 3-((3,4-dihydroxyphenylethyl)dimethylammonium)propane-1-sulfonate (ZDS, 100 mg) and sodium bicarbonate (60 mg) were dissolved in a mixture of ultrapure water (20 mL) and acetone (20 mL), and the reaction was carried out under argon protection with stirring. Subsequently, a solution of chloroform (10 mL) containing oil-soluble ultrafine ferrite nanoparticles (140 mg) was added to the above mixture, and the reaction was carried out at 37 °C with stirring for 4 hours. After the time was completed, the reaction solution was centrifuged at low speed to separate the layers, and the upper layer was collected. The acetone in the upper layer was removed by rotary evaporation. The remaining solution was washed three times with ultrapure water by ultrafiltration and then freeze-dried to obtain ultrafine ferrite nanoprobe solid powder for later use.

[0076] The yields of the zinc-doped zwitterionic ligand-modified nanoprobe (ZFO-ZDS) in Example 1 and the undoped zwitterionic molecule-modified nanoprobe (FO-ZDS) in Comparative Example 3 were compared, and the results are as follows: Figure 10 As shown.

[0077] Figure 10 The results showed that zinc doping allowed the nanoparticles to be better modified by zwitterionic molecules, and the yield of Example 1 was significantly higher than that of Comparative Example 3 without zinc doping.

[0078] Comparative Example 4 Preparation of zwitterionic-modified ultrasmall manganese ferrite nanoprobes: Step 1: Dissolve a mixture of ferric erucic acid (1 mmol), manganese oleate (1 mmol), oleyl alcohol (6 mmol), and oleic acid (2 mmol) in diphenyl ether (20 mL) at room temperature; stir the reaction mixture at 110 °C under vacuum for 30 minutes to remove water from the reaction system; increase the temperature of the reaction system to 265 °C at a rate of 5 °C / min under stirring and argon protection, and maintain this temperature for 30 minutes; after the time is up, rapidly cool the reaction system to room temperature, purify it by centrifugation using cyclohexane and anhydrous ethanol, and vacuum dry to obtain oil-soluble ultrafine manganese ferrite nanoparticles for later use.

[0079] Step 2: 3-((3,4-dihydroxyphenylethyl)dimethylammonium)propane-1-sulfonate (ZDS, 100 mg) and sodium bicarbonate (60 mg) were dissolved in a mixture of ultrapure water (20 mL) and acetone (20 mL), and the reaction was carried out under argon protection with stirring. Subsequently, a solution of chloroform (10 mL) containing oil-soluble ultrafine manganese ferrite nanoparticles (140 mg) was added to the above mixture, and the reaction was carried out at 37 °C with stirring for 4 hours. After the time was completed, the reaction solution was centrifuged at low speed to separate the layers, and the upper layer was collected. The acetone in the upper layer was removed by rotary evaporation. The remaining solution was washed three times with ultrapure water by ultrafiltration and then freeze-dried to obtain ultrafine manganese ferrite nanoparticle probe solid powder for later use.

[0080] The abdominal enhanced magnetic resonance imaging (MRI) effect of the product of Comparative Example 4 was tested, including the following steps: The metabolic behavior of nanoparticles was studied in rats using MRI. Ultrasmall manganese ferrite nanoprobes were intravenously injected into rats. Subsequently, coronal T1-weighted MRI of the abdomen was performed at different time points, and the signal values ​​of the imaging results were measured and analyzed.

[0081] Figure 7Coronal imaging results showed that the liver enhanced within 5 minutes after injection of the ultra-small manganese ferrite nanoprobe, followed by a significant "darkening" of the liver, exhibiting T2WI imaging effects. This demonstrates that the ultra-small manganese ferrite nanoprobe was significantly enriched in the liver, and this "darkening" effect was more pronounced in the subsequent 3 hours, lasting for more than 24 hours. The kidneys showed significant enhancement within 5 minutes after injection, followed by a gradual decrease in enhancement. A "bright ring" appeared at the corticomedullary junction 3 to 24 hours after injection, while other renal areas returned to pre-injection levels, indicating that the ultra-small manganese ferrite nanoprobe was retained at the corticomedullary junction. In contrast, the ultra-small zinc ferrite nanoprobe in Example 1 did not show prolonged kidney retention, indicating higher safety. Figure 7 (a) offers higher security.

[0082] This invention employs a highly efficient and low-cost synthesis strategy to construct ultrasmall zinc ferrite nanoprobes modified with zwitterionic ligands, achieving synthesis with ultrasmall particle size and high dispersibility. This enables high-sensitivity T1-weighted magnetic resonance imaging (MRI) and fully meets the practical needs of clinical applications and animal experiments. The core advantages of this invention's synthesis strategy lie in its biosafety and clinical applicability, particularly highlighting the following key characteristics: First, it achieves rapid renal clearance of the nanoparticles, effectively eliminating them through renal metabolism and avoiding long-term accumulation in the body; second, it significantly reduces liver enrichment levels, decreasing non-specific adsorption to liver tissue and reducing organ burden; third, it achieves no retention even in cases of kidney injury, ensuring biosafety even in states of abnormal kidney function, fundamentally reducing the potential risks of nanomaterial applications. This invention provides a practical and easily scalable technical solution for the development and clinical translation of safe, efficient, and renally clearable magnetic resonance contrast agents.

[0083] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, not all embodiments. People can obtain other embodiments based on the present invention without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. An ultra-small zinc ferrite nanoprobe, characterized in that, The ultra-small zinc ferrite nanoprobe contains zinc ferrite nanoparticles and zwitterionic molecules, wherein the molar ratio of iron to zinc is 0.5 to 10:1, and the zwitterionic molecules are modified on the surface of zinc ferrite nanoparticles by coordination with metal elements through a catechol structure. The ultrasmall zinc ferrite nanoprobe also possesses the following properties: (1) The crystal core size is less than 5 nm; (2) Hydrodynamic size is less than 8 nm; (3) Under a magnetic field of 3.0 T, the longitudinal relaxation rate is greater than 2 mM. -1 ·s -1 The ratio of lateral to longitudinal relaxation rate is less than 1.

5.

2. The ultra-small zinc ferrite nanoprobe according to claim 1, characterized in that, The zwitterionic molecules include 3-((3,4-dihydroxyphenylethyl)dimethylammonium)propane-1-sulfonate, 3-((3,4-dihydroxyphenylethyl)dimethylammonium)propane-1-carboxylate, 3-hydroxy-L-tyrosine, or 3-((3-((2-amino-3-(3,4-dihydroxyphenyl)propionyl)oxy)propyl)dimethylammonium)propane-1-sulfonate).

3. The method for preparing the ultrasmall zinc ferrite nanoprobe according to claim 1 or 2, characterized in that, Includes the following steps: (1) Iron precursor, zinc precursor, ligand and organic solvent were mixed according to stoichiometric ratio and thermally decomposed under inert gas protection to prepare oil-soluble ultra-small zinc ferrite nanoparticles. (2) The oil-soluble ultra-small zinc ferrite nanoparticles described in step (1) are dispersed in an organic solvent, and the zwitterionic molecules and alkali metal salts are dispersed in a mixed solvent of water and acetone. Under the protection of an inert gas, the two solutions are mixed and reacted to allow the ligands on the surface of the oil-soluble ultra-small zinc ferrite nanoparticles to exchange ligands with the zwitterionic molecules, thereby obtaining ultra-small zinc ferrite nanoprobes.

4. The preparation method according to claim 3, characterized in that, The iron precursor includes one or more of the following: ferric nitrate, ferric sulfate, ferric acetate, ferric chloride, ferric stearate, ferric pentacarbonyl, ferric acetylacetone, ferric erucic acid, and ferric oleate.

5. The preparation method according to claim 3, characterized in that, The zinc precursor includes one or more of zinc nitrate, zinc sulfate, zinc acetate, zinc chloride, zinc acetylacetone, and basic zinc carbonate.

6. The preparation method according to claim 3, characterized in that, The molar ratio of the iron precursor to the zinc precursor is 1:0.1~3.

7. The preparation method according to claim 3, characterized in that, The temperature of the thermal decomposition reaction is 220~320℃.

8. The preparation method according to claim 7, characterized in that, The temperature for the thermal decomposition reaction is maintained for 5 minutes to 2 hours.

9. The preparation method according to claim 3, characterized in that, The mass ratio of the oil-soluble ultrasmall zinc ferrite nanoparticles to zwitterionic molecules is 0.1~3:1; the organic solvent for dispersing the oil-soluble ultrasmall zinc ferrite nanoparticles includes dichloromethane, trichloromethane, cyclohexane or n-hexane.

10. The application of the ultrasmall zinc ferrite nanoprobe according to claim 1 or 2 or the ultrasmall zinc ferrite nanoprobe obtained by the preparation method according to any one of claims 3 to 9 as a magnetic resonance imaging contrast agent.

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