A trace cobalt-doped magnetic nanoparticle, a preparation method and application thereof

Abstract

The application discloses a kind of trace cobalt doped magnetic nanoparticles and preparation method and application thereof, it is related to magnetic nanometer material technical field.The method the magnetic nanoparticles are cobalt ferrite, chemical formula is Co x Fe 3‑x O4, wherein, 0 < x ≤ 0.1;Cobalt ion in the cobalt ferrite is doped in lattice surface octahedral site.Through site selective doping cobalt ion to specific site in lattice, the synchronous regulation of dynamic magnetization characteristics is realized.Through the accurate control of cobalt doping amount, the magnetization intensity ( Ms ) of magnetic nanoparticle is significantly improved, and the relaxation time ( τ ) is adjusted, so that MPI signal and MHT curative effect are significantly improved.

Description

Technical Field

[0001] This invention relates to the field of magnetic nanomaterials technology, specifically to a micro-cobalt-doped magnetic nanoparticle, its preparation method, and its application. Background Technology

[0002] Magnetic particle imaging (MPI) is an emerging medical imaging technique based on the interaction between magnetic nanoparticles (MNPs) and a magnetic field. Unlike traditional magnetic resonance imaging (MRI), MPI directly images the spatial distribution of MNPs by detecting changes in their nonlinear magnetic response in a magnetic field. Compared to traditional imaging methods such as CT, MRI, and ultrasound, MPI offers advantages such as no background signal interference, no penetration depth limitations, quantifiable signals, and no ionizing radiation. Magnetic hyperthermia therapy (MHT) is a novel cancer treatment technology that utilizes the heat-generating properties of MNPs under an alternating magnetic field to transfer heat to tumor tissue to kill tumor cells. It features non-invasiveness, low toxicity, high penetration, and localized heat generation.

[0003] Magnetic particle imaging-guided magnetothermal therapy (MPI-MHT) directly utilizes the heat-generating properties of molecularly active substances (MNPs) to kill tumors without the need for additional therapeutic payloads. This technology allows for localized heating of the lesion area, avoiding damage to healthy organs containing high concentrations of MNPs, thus significantly improving treatment selectivity. Furthermore, MPI has the ability to quantitatively assess MNP distribution, providing a basis for MHT dosage control, and can precisely locate MNP-rich areas, accurately identifying lesion locations. This enables MHT to adaptively adjust the heating strategy based on the MNP concentration in different areas, further enhancing treatment specificity. This not only helps achieve highly efficient killing of malignant tumors but also helps to maximize the protection of normal tissues.

[0004] To achieve precise guidance and dosage assessment of MHT using MPI (Magnetic Sensing Imaging), developing MNPs that combine excellent MPI imaging performance with magnetocaloric conversion capabilities is crucial. However, existing research indicates an inherent conflict between the magnetic performance requirements of MNPs imposed by MPI tracers and magnetocaloric agents: for example, increased coercivity and relaxation can lead to weakening of the MPI signal. In MHT applications, however, increased coercivity and relaxation within a certain range have been shown to enhance heat generation. Because it is difficult to simultaneously achieve high imaging sensitivity and high thermal conversion efficiency under safe dosage and applied magnetic field conditions, efficient synergistic optimization of these two performances in a therapeutic context has not yet been achieved in preclinical studies. Summary of the Invention

[0005] To address the shortcomings of the aforementioned background technology, this invention primarily solves the problem that existing clinically approved and widely used magnetic particles cannot simultaneously meet the dual requirements of imaging signal intensity and tumor ablation heat within a safe dosage range. This invention provides a trace amount of cobalt-doped magnetic nanoparticles, their preparation method, and their applications. The magnetic nanoparticles provided by this invention are cobalt ferrite (Co... x Fe 3-x O4), through site-selective doping of cobalt ions (Co) 2+ By precisely controlling the amount of cobalt doping at specific sites within the crystal lattice (preferably octahedral sites on the surface), the dynamic magnetization properties of the magnetic nanoparticles were synchronously regulated. This significantly improved the magnetization intensity of the magnetic nanoparticles. Ms ), and adjusted the relaxation time ( τ This significantly enhances MPI signal strength and MHT efficacy. Compared to traditional magnetic nanoparticles, the magnetic nanoparticles prepared in this invention exhibit significantly improved MPI signal intensity and specific absorption rate. Furthermore, by surface modification with targeting molecules (such as prostate-specific membrane antigen), these magnetic nanoparticles can achieve highly efficient imaging diagnosis and ablation of tumors. The nanoparticles provided by this invention have broad application prospects in the field of tumor diagnosis and treatment.

[0006] The first objective of this invention is to provide a trace amount of cobalt-doped magnetic nanoparticles, wherein the magnetic nanoparticles are cobalt ferrite with the chemical formula Co. x Fe 3-x O4, where 0 <x≤ 0.1;

[0007] Cobalt ions in the cobalt ferrite are doped at octahedral sites on the crystal lattice surface.

[0008] Preferably, the magnetic nanoparticles have a magnetic susceptibility of 100-150 emu·g. -1 Fe has a relaxation time of 0-100 μs.

[0009] Preferably, the magnetic nanoparticles have a particle size of 10-20 nm.

[0010] The second objective of this invention is to provide a method for preparing trace amounts of cobalt-doped magnetic nanoparticles, comprising the following steps:

[0011] Preparation of cobalt oleate and iron oleate;

[0012] Cobalt oleate was dissolved in n-hexane to obtain a cobalt oleate solution; iron oleate was dissolved in 1-octadecene, then the cobalt oleate solution was added, followed by the addition of oleic acid to obtain a mixed solution;

[0013] The mixed solution was heated to 100-120℃ and held for 25-35 min, during which gas was continuously evacuated. After reaching the holding temperature, nitrogen gas was introduced and gas was evacuated again, which was repeated 2-3 times. Then, nitrogen gas was introduced and the reaction continued for 25-35 min. The temperature was then increased to 190-210℃ and held for 25-35 min. The temperature was then increased to 310-320℃ and held for 10-20 h. After the reaction was completed, the solution was cooled to room temperature to obtain trace cobalt-doped magnetic nanoparticles.

[0014] Preferably, when preparing the mixed solution, the molar ratio of cobalt oleate to iron oleate is (0.001~1):(29~30).

[0015] Preferably, the cobalt oleate or iron oleate is prepared according to the following steps:

[0016] Cobalt or iron salts are uniformly dispersed in a mixed solvent of water and n-hexane, followed by the addition of sodium oleate. After refluxing at 75-85°C for 3-5 hours, the reactants are extracted and separated. The upper organic phase is extracted, washed, and dried to obtain cobalt oleate or iron oleate.

[0017] The molar ratio of the cobalt salt or iron salt to sodium oleate is 1:2~3.

[0018] Preferably, after cooling to room temperature, it further includes:

[0019] After the reaction is complete, transfer the solution to a centrifuge tube, add n-hexane, mix thoroughly, then add anhydrous ethanol, shake to mix, and then centrifuge to remove the supernatant and retain the precipitate.

[0020] Repeat the following washing steps three times for the precipitate: add n-hexane, mix well, then add anhydrous ethanol, shake to mix well; centrifuge at 5000~8000 rpm for 5~10 min, and discard the supernatant.

[0021] The third objective of this invention is to provide the application of trace cobalt-doped magnetic nanoparticles in the preparation of diagnostic or therapeutic tumor drugs. In the preparation of diagnostic or therapeutic tumor drugs, the surface of the magnetic nanoparticles is modified with a biocompatible ligand and a targeting molecule; wherein, the biocompatible ligand is maleic anhydride-1-octadecene; and the targeting molecule is Raw264.7 macrophage membrane with affinity for prostate-specific membrane antigen.

[0022] The fourth objective of this invention is to provide a method for preparing diagnostic or therapeutic tumor drugs using trace amounts of cobalt-doped magnetic nanoparticles, comprising the following steps:

[0023] Macrophage membranes were extracted and dispersed in PBS, and then mixed with trace amounts of cobalt-doped magnetic nanoparticles dispersed in an aqueous solvent to obtain a mixture.

[0024] After sonicating the mixture in a cell disruptor for 20-40 minutes, the mixture is then circulated and extruded 8-10 times through an extruder to obtain micro-cobalt-doped magnetic nanoparticles with cell membranes modified on the surface.

[0025] The fifth objective of this invention is to provide the application of trace cobalt-doped magnetic nanoparticles in magnetic particle imaging probes or magnetothermal therapy agents.

[0026] Compared with the prior art, the beneficial effects of the present invention are:

[0027] This invention provides a trace amount of cobalt-doped magnetic nanoparticles, their preparation method, and applications. The magnetic nanoparticles provided by this invention are cobalt ferrite (Co). x Fe 3-x O4), through site-selective doping of cobalt ions (Co) 2+ By targeting specific sites within the crystal lattice, preferably surface octahedral sites (Oh-surf), synchronous control of dynamic magnetization characteristics is achieved.

[0028] This invention effectively solves the technical problem of the difficulty in synergistic performance of MPI and MHT through an innovative low-concentration doping strategy. By precisely controlling the introduction of trace amounts of cobalt precursors during the reaction crystallization process, this invention achieves selective and precise micro-doping of cobalt at octahedral (Oh) sites on the surface of magnetic nanoparticles. This strategy effectively optimizes the magnetic anisotropy of nanoparticles without disrupting the crystal structure, enabling them to simultaneously achieve extremely high dynamic magnetic susceptibility and a suitable relaxation time, laying a materials science foundation for achieving both high-performance MPI and MHT functions.

[0029] The magnetic nanoparticles provided by this invention exhibit significantly improved performance and superior effects, as fully demonstrated by experimental data. In vitro testing results show that the MPI imaging signal intensity of the trace cobalt-doped magnetic nanoparticles prepared by this invention is 7.4 times that of commercially available magnetic particles like VivoTrax; its magnetocaloric conversion efficiency is significantly improved, with a specific absorption rate (SAR value) 12 times that of VivoTrax. This significant performance improvement proves that this invention successfully solves the technical challenge of balancing high MPI sensitivity with high MHT efficiency.

[0030] The magnetic nanoparticles provided by this invention have broad application prospects in integrated diagnosis and treatment. After surface engineering modification of macrophage membranes with affinity for prostate-specific membrane antigen (PSMA), these magnetic nanoparticles exhibit excellent tumor-targeting enrichment ability and highly efficient thermal ablation therapeutic effect in in vivo experiments. This fully demonstrates their great application potential as an integrated MPI-MHT diagnostic and therapeutic agent.

[0031] In summary, this invention solves the core contradiction in the development of MPI-MHT therapeutic agents by using the key technology of trace cobalt doping. The magnetic nanoparticle materials provided have achieved significant performance improvements and have good application prospects. Attached Figure Description

[0032] Figure 1 Electron microscopy images of the morphology of the trace cobalt-doped magnetic nanoparticles provided in Examples 1-4.

[0033] Figure 2 The magnetization curve test results are for the trace cobalt-doped magnetic nanoparticles provided in Examples 1-4.

[0034] Figure 3 The results of the spectral attenuation and relaxation time tests of the trace cobalt-doped magnetic nanoparticles provided in Example 1 are shown.

[0035] Figure 4 The MPI signal intensity of the trace cobalt-doped magnetic nanoparticles provided in Example 1, the iron oxide magnetic particles provided in Comparative Example 1, and the VivoTrax commercial magnetic particles of the same concentration were compared.

[0036] Figure 5 A comparison of the magnetocaloric properties of the trace cobalt-doped magnetic nanoparticles provided in Example 1, the iron oxide magnetic particles provided in Comparative Example 1, and the commercially available magnetic particles VivoTrax.

[0037] Figure 6 Magnetothermal stability test of trace cobalt-doped magnetic nanoparticles provided in Example 1.

[0038] Figure 7 The results show the calculated magnetocaloric absorption ratios of the trace cobalt-doped magnetic nanoparticles provided in Example 1, the iron oxide magnetic particles provided in Comparative Example 1, and commercial magnetic particles.

[0039] Figure 8 Electron micrograph of the surface of the cobalt-doped magnetic nanoparticles provided in Example 5 after modification with a cell membrane.

[0040] Figure 9 The results are from in vivo MPI signal testing in mice.

[0041] Figure 10 The results are from in vivo magnetocaloric temperature tests in mice. Detailed Implementation

[0042] To enable those skilled in the art to better understand and implement the technical solutions of the present invention, the present invention will be further described below in conjunction with specific embodiments and accompanying drawings. However, the embodiments described are not intended to limit the present invention.

[0043] This invention addresses the inherent contradiction in the magnetic performance requirements of magnetic particles in magnetic particle imaging (MPI) and magnetic hyperthermia therapy (MHT). Existing clinically approved and widely used magnetic particles struggle to simultaneously meet the dual requirements of imaging signal intensity and tumor ablation heat within a safe dosage range. This invention employs an atomic-scale doping strategy to modulate the magnetic structure of materials, thereby balancing the performance demands of MPI-MHT and constructing a high-performance, therapeutically integrated magnetic particle formulation, which is of paramount importance.

[0044] The purpose of this invention is to provide trace cobalt-doped magnetic nanoparticles that possess both superparamagnetism and ferromagnetism, controllable coercivity, and moderate relaxation time. These nanoparticles can generate sensitive imaging signals under commercial magnetic particle imaging equipment and produce sufficient heating effects under high-frequency magnetocaloric instruments. This magnetic nanomaterial exhibits spin order and tunable anisotropy, enabling stable dispersion in aqueous systems. It demonstrates excellent MPI imaging and MHT effects, and holds promise for achieving high-performance integrated MPI-MHT diagnosis and treatment, which is of great significance for advancing the clinical translation of MPI-MHT.

[0045] To achieve the above objectives, a first aspect of the present invention provides a trace amount of cobalt-doped magnetic nanoparticles, wherein the magnetic nanoparticles are cobalt ferrite with the chemical formula Co. x Fe 3-x O4, where 0 <x≤ 0.1;

[0046] Cobalt ions in the cobalt ferrite are doped at octahedral sites on the crystal lattice surface.

[0047] The magnetic nanoparticles have a magnetic susceptibility of 100-150 emu·g. -1 Fe, with a relaxation time of 0-100 μs. The magnetic nanoparticles have a particle size of 10-20 nm.

[0048] The magnetic nanoparticles provided by this invention are cobalt ferrite (Co). x Fe 3-x O4), through site-selective doping of cobalt ions (Co) 2+ By precisely controlling the amount of cobalt doping at specific sites within the crystal lattice, preferably octahedral sites (Oh-surf), the dynamic magnetization properties of the magnetic nanoparticles were synchronously regulated. Ms ), and adjusted the relaxation time ( τ This significantly enhances MPI signaling and MHT efficacy. Furthermore, its surface can be biocompatiblely modified for in vivo application.

[0049] A second aspect of this invention provides a method for preparing trace amounts of cobalt-doped magnetic nanoparticles, comprising the following steps:

[0050] Preparation of cobalt oleate and iron oleate;

[0051] Cobalt oleate was dissolved in n-hexane to obtain a cobalt oleate solution; iron oleate was dissolved in 1-octadecene, then the cobalt oleate solution was added, followed by the addition of oleic acid to obtain a mixed solution;

[0052] The mixed solution was heated to 100-120℃ and held for 25-35 min, during which gas was continuously evacuated. After reaching the holding temperature, nitrogen gas was introduced and gas was evacuated again, which was repeated 2-3 times. Then, nitrogen gas was introduced and the reaction continued for 25-35 min. The temperature was then increased to 190-210℃ and held for 25-35 min. The temperature was then increased to 310-320℃ and held for 10-20 h. After the reaction was completed, the solution was cooled to room temperature to obtain trace cobalt-doped magnetic nanoparticles.

[0053] When preparing the mixed solution, the molar ratio of cobalt oleate to iron oleate is (0.001~1):(29~30).

[0054] After cooling to room temperature, it also includes:

[0055] After the reaction is complete, transfer the solution to a centrifuge tube, add n-hexane, mix thoroughly, then add anhydrous ethanol, shake to mix, and then centrifuge to remove the supernatant and retain the precipitate.

[0056] Repeat the following washing steps three times for the precipitate: add n-hexane, mix well, then add anhydrous ethanol, shake to mix well; centrifuge at 5000~8000 rpm for 5~10 min, and discard the supernatant.

[0057] The cobalt oleate or iron oleate is prepared according to the following steps:

[0058] Cobalt or iron salts are uniformly dispersed in a mixed solvent of water and n-hexane, followed by the addition of sodium oleate. After refluxing at 75-85°C for 3-5 hours, the reactants are extracted and separated. The upper organic phase is extracted, washed, and dried to obtain cobalt oleate or iron oleate.

[0059] The molar ratio of the cobalt salt or iron salt to sodium oleate is 1:2~3.

[0060] An exemplary method for preparing trace amounts of cobalt-doped magnetic nanoparticles includes:

[0061] Step 1: Preparation of ferric oleate: First, 3.6 g of FeCl3·6H2O was dissolved in a mixed solution consisting of 15 mL of deionized water and 15 mL of n-hexane. Then, 12.2 g of sodium oleate was added, and the mixture was heated under reflux in an oil bath at 80 °C for 4 h with magnetic stirring. After the reaction was complete, the mixture was transferred to a separatory funnel for extraction and separation. The upper organic phase was extracted and washed three times with water. Finally, n-hexane was removed using a rotary evaporator to obtain a brown gelatinous liquid, which was then dried under vacuum for 12 h.

[0062] Preparation of cobalt oleate: First, 130 mg of CoCl2 was dissolved in a mixed solution consisting of 15 mL of deionized water and 15 mL of n-hexane. Then, 608 mg of sodium oleate was added, and the mixture was heated under reflux in an oil bath at 80 °C for 4 h with magnetic stirring. After the reaction was complete, the mixture was transferred to a separatory funnel for extraction and separation. The upper organic phase was extracted and washed three times with water. Finally, n-hexane was removed using a rotary evaporator to obtain a purple gelatinous liquid, which was dried under vacuum for 12 h. Subsequently, it was stored under vacuum after degassing to prevent oxidation of the divalent cobalt.

[0063] Step 2: Mix cobalt oleate and iron oleate in a specific ratio: By changing the precursor feed ratio, the amount of Co doping in the iron oxide magnetic particles is controlled to obtain a mixed solution of Co in the iron oxide magnetic particle precursor.

[0064] Step 3: The mixed solution obtained in Step 2 is subjected to high-temperature solution annealing to obtain magnetic nanoparticles with trace amounts of cobalt doping.

[0065] The solution obtained in step 2 was first heated to 120℃ and held for 30 min, with continuous evacuation during heating. After reaching the holding temperature, nitrogen gas was introduced and evacuation was repeated three times. Nitrogen gas was then introduced and the reaction continued for another 30 min. The temperature was then raised to 200℃ and held for 30 min, and finally raised to 310℃ and held for 10 h. After the reaction, the solution was cooled to room temperature. The resulting solution was transferred to a 50 mL centrifuge tube, and 1 mL of n-hexane was added and mixed thoroughly. Then, 5 mL of anhydrous ethanol was added and the mixture was shaken for 1 min. The mixture was centrifuged at 6000 rpm for 6 min; the supernatant was removed, and the precipitate was retained. The precipitate was washed three times using the following steps: 5 mL of n-hexane was added and mixed; then 5 mL of anhydrous ethanol was added and the mixture was shaken for 1 min; the mixture was centrifuged at 6000 rpm for 6 min, and the supernatant was discarded. Finally, the washed precipitate was redispersed in 5 mL of chloroform. By changing the precursor feed ratio, magnetic nanoparticles with different trace amounts of Co doping were synthesized. Trace Co-doped magnetic nanoparticles include Co 0.01 Fe 2.99 O4, Co 0.03 Fe 2.97 O4, Co0.05 Fe 2.95 O4 or Co 0.1 Fe 2.95 O4.

[0066] It should be noted that the evacuation is performed during this period to remove air and moisture from the bottle and prevent oxidation during the synthesis of magnetic particles.

[0067] A third aspect of this invention provides the application of trace cobalt-doped magnetic nanoparticles in the preparation of diagnostic or therapeutic tumor drugs. In the preparation of diagnostic or therapeutic tumor drugs, the surface of the magnetic nanoparticles is modified with a biocompatible ligand and a targeting molecule; wherein the biocompatible ligand is maleic anhydride-1-octadecene; and the targeting molecule is Raw264.7 macrophage membrane with affinity for prostate-specific membrane antigen.

[0068] A fourth aspect of this invention provides a method for preparing diagnostic or therapeutic tumor drugs using trace amounts of cobalt-doped magnetic nanoparticles, comprising the following steps:

[0069] Macrophage membranes were extracted and dispersed in PBS, and then mixed with trace amounts of cobalt-doped magnetic nanoparticles dispersed in an aqueous solvent to obtain a mixture.

[0070] After sonicating the mixture in a cell disruptor for 20-40 minutes, the mixture is then circulated and extruded 8-10 times through an extruder to obtain micro-cobalt-doped magnetic nanoparticles with cell membranes modified on the surface.

[0071] An exemplary method for preparing diagnostic or therapeutic tumor drugs using trace amounts of cobalt-doped magnetic nanoparticles includes:

[0072] Surface modification of the particles was performed using maleic anhydride-1-octadecene (PMH): 1 g of maleic anhydride-1-octadecene (PMH) was weighed and dissolved in 5 mL of chloroform. The chloroform solution of the magnetic particles was slowly added dropwise to the PMH solution while continuously stirring magnetically. Stirring was continued at room temperature for 4 h to ensure that PMH was fully coated on the surface of the oil-phase magnetic particles. After the reaction was complete, the chloroform in the solution was removed using a rotary evaporator to obtain a black crystalline solid (PMH-modified magnetic particles).

[0073] Weigh 1 g of 4-dimethylaminopyridine (DMAP) and dissolve it in 10 mL of deionized water. Add the obtained black crystalline solid to the DMAP solution and sonicate in a water bath until the solid is completely dissolved. Then, centrifuge with deionized water at 16000 rpm for 2 h, and repeat the washing three times. Each time, discard the supernatant and redisperse the precipitate with deionized water to finally obtain aqueously dispersed magnetic particles.

[0074] Surface engineering of magnetic particles using genetically engineered macrophages: Genetically engineered macrophages were seeded onto 100 mm... 2 The cells were cultured in petri dishes at 37°C in a 5% CO2 incubator to allow them to adhere fully. Subsequently, all cells were washed off the petri dishes with phosphate-buffered saline (PBS), transferred to 15 mL centrifuge tubes, and centrifuged at 1700 rpm for 10 min. The resulting cell pellet was obtained.

[0075] A mixture of cell membrane protein extraction reagent A and protease inhibitor (PMSF) was added to the centrifuged cell pellet and placed in an ice bath for 15 min. Subsequently, the pellet was rapidly frozen in liquid nitrogen and allowed to thaw naturally at room temperature; this freeze-thaw cycle was repeated 5 times. Afterward, the pellet was centrifuged at 1700 rpm for 10 min, the supernatant was collected, and then centrifuged again at 13000 rpm for 30 min to obtain the genetically engineered macrophage cell membrane. It should be noted that plasma protein extraction reagent A is referred to as the first lysis buffer or pre-lysis buffer.

[0076] Cell membrane proteins, plasma protein extraction reagent A, and protease inhibitor (PMSF) were all purchased from Beyotime Biotechnology.

[0077] Preparation of macrophage membrane-encapsulated magnetic particles: Macrophage membrane-encapsulated magnetic particles were prepared using an ultrasonic method and a physical extrusion method: Macrophage membranes were dispersed in PBS and mixed with trace amounts of cobalt-doped magnetic nanoparticles dispersed in an aqueous solvent, wherein the mixing ratio was 1:1 to 2:1 by mass of cell membrane to magnetic nanoparticles; the mixture was ultrasonicated in a cell disruptor for 30 min, and then the mixture was circulated and extruded 10 times through an extruder to obtain macrophage membrane-encapsulated magnetic particles.

[0078] The magnetic nanoparticles provided by this invention enable precise localization and quantification of tumors through magnetic particle imaging; and achieve effective tumor ablation through magnetothermal therapy. For tumor diagnosis and treatment, prostate cancer is a preferred candidate.

[0079] The fifth aspect of this invention provides the application of trace cobalt-doped magnetic nanoparticles in magnetic particle imaging probes or magnetothermal therapy agents.

[0080] The magnetic nanoparticles provided by this invention, when used as magnetic particle imaging probes, should produce an imaging signal 7.4 times that of commercially available magnetic particles VivoTrax. The magnetic nanoparticles provided by this invention, when used as magnetothermal therapy agents, should have a magnetothermal specific absorption rate 12 times that of commercially available magnetic particles VivoTrax.

[0081] It should be noted that, unless otherwise specified, the experimental methods used in this invention are all conventional methods; and the reagents and materials used, unless otherwise specified, are all commercially available.

[0082] Example 1

[0083] A type of magnetic nanoparticle doped with trace amounts of cobalt (Co) 0.05 Fe 2.95 The preparation method of O4 includes the following steps:

[0084] Preparation of ferric oleate: 3.6 g of FeCl3·6H2O was dissolved in a mixed solution consisting of 15 mL of deionized water and 15 mL of n-hexane. Then, 12.2 g of sodium oleate was added, and the mixture was heated under reflux in an oil bath at 80 °C for 4 h with magnetic stirring. After the reaction was complete, the mixture was transferred to a separatory funnel for extraction and separation. The upper organic phase was extracted and washed three times with water. Finally, n-hexane was removed using a rotary evaporator to obtain a brown colloidal liquid, which was dried under vacuum for 12 h to obtain ferric oleate.

[0085] Preparation of cobalt oleate: 130 mg of CoCl2 was dissolved in a mixed solution consisting of 15 mL of deionized water and 15 mL of n-hexane. Then, 608 mg of sodium oleate was added, and the mixture was heated under reflux in an oil bath at 80 °C for 4 h with magnetic stirring. After the reaction was complete, the mixture was transferred to a separatory funnel for extraction and separation. The upper organic phase was extracted and washed three times with water. Finally, n-hexane was removed using a rotary evaporator to obtain a purple gelatinous liquid, which was dried under vacuum for 12 h. Subsequently, it was vacuum-stored after degassing to prevent oxidation of divalent cobalt, thus obtaining cobalt oleate.

[0086] First, dissolve 31.1 mg of cobalt oleate in 1 mL of n-hexane. Then, dissolve 2.66 g of ferric oleate in a three-necked flask containing 15 mL of 1-octadecene. Add the hexane solution of cobalt oleate to the flask, and then add 200 μL of oleic acid to obtain a mixed solution.

[0087] The mixed solution was heated to 120°C and held for 30 min, with continuous evacuation during heating. After reaching the holding temperature, nitrogen gas was introduced and evacuation was repeated three times. Nitrogen gas was then introduced and the reaction continued for another 30 min. The temperature was then increased to 200°C and held for 30 min, and then increased to 310°C and held for 10 h. After the reaction was completed, the solution was cooled to room temperature. The resulting solution was transferred to a 50 mL centrifuge tube, 1 mL of n-hexane was added, and the mixture was thoroughly mixed. Then, 5 mL of anhydrous ethanol was added, and the mixture was shaken for 1 min. The mixture was then centrifuged at 6000 rpm for 6 min, the supernatant was removed, and the precipitate was retained.

[0088] Repeat the following washing steps three times for the precipitate: add 5 mL of n-hexane and mix well; then add 5 mL of anhydrous ethanol and shake to mix for 1 min; centrifuge at 6000 rpm for 6 min and discard the supernatant.

[0089] The washed precipitate was redispersed in 5 mL of chloroform to maintain good dispersibility and ensure aqueous phase transfer. This yielded trace cobalt-doped magnetic nanoparticles (Co). 0.05 Fe 2.95 O4.

[0090] Example 2

[0091] A type of magnetic nanoparticle doped with trace amounts of cobalt (Co) 0.01 Fe 2.95 The preparation method of O4 includes the following steps:

[0092] Preparation of ferric oleate: 3.6 g of FeCl3·6H2O was dissolved in a mixed solution consisting of 15 mL of deionized water and 15 mL of n-hexane. Then, 12.2 g of sodium oleate was added, and the mixture was heated under reflux in an oil bath at 80 °C for 4 h with magnetic stirring. After the reaction was complete, the mixture was transferred to a separatory funnel for extraction and separation. The upper organic phase was extracted and washed three times with water. Finally, n-hexane was removed using a rotary evaporator to obtain a brown colloidal liquid, which was dried under vacuum for 12 h to obtain ferric oleate.

[0093] Preparation of cobalt oleate: 130 mg of CoCl2 was dissolved in a mixed solution consisting of 15 mL of deionized water and 15 mL of n-hexane. Then, 608 mg of sodium oleate was added, and the mixture was heated under reflux in an oil bath at 80 °C for 4 h with magnetic stirring. After the reaction was complete, the mixture was transferred to a separatory funnel for extraction and separation. The upper organic phase was extracted and washed three times with water. Finally, n-hexane was removed using a rotary evaporator to obtain a purple gelatinous liquid, which was dried under vacuum for 12 h. Subsequently, it was vacuum-stored after degassing to prevent oxidation of divalent cobalt, thus obtaining cobalt oleate.

[0094] Dissolve 6.22 mg of cobalt oleate in 1 mL of n-hexane, then dissolve 2.69 g of ferric oleate in a three-necked flask containing 15 mL of 1-octadecene, add the hexane solution of cobalt oleate to the flask, and then add 200 μL of oleic acid to obtain a mixed solution.

[0095] The mixed solution was heated to 120℃ and held for 30 min, with continuous evacuation during heating. After reaching the holding temperature, nitrogen gas was introduced and evacuation was repeated three times. Nitrogen gas was then introduced and the reaction continued for 30 min. The temperature was then increased to 200℃ and held for 30 min, and then increased to 310℃ and held for 10 h. After the reaction was completed, the solution was cooled to room temperature. The resulting solution was transferred to a 50 mL centrifuge tube, 1 mL of n-hexane was added, and the mixture was thoroughly mixed. Then, 5 mL of anhydrous ethanol was added, and the mixture was shaken for 1 min. The solution was centrifuged at 6000 rpm for 6 min, the supernatant was removed, and the precipitate was retained.

[0096] Repeat the following washing steps three times for the precipitate: add 5 mL of n-hexane and mix well; then add 5 mL of anhydrous ethanol and shake to mix for 1 min; centrifuge at 6000 rpm for 6 min and discard the supernatant.

[0097] The washed precipitate was redispersed in 5 mL of chloroform to maintain good dispersibility and ensure aqueous phase transfer. This yielded trace cobalt-doped magnetic nanoparticles (Co). 0.01 Fe 2.99 O4.

[0098] Example 3

[0099] A type of magnetic nanoparticle doped with trace amounts of cobalt (Co) 0.03 Fe 2.95 The preparation method of O4 includes the following steps:

[0100] Preparation of ferric oleate: 3.6 g of FeCl3·6H2O was dissolved in a mixed solution consisting of 15 mL of deionized water and 15 mL of n-hexane. Then, 12.2 g of sodium oleate was added, and the mixture was heated under reflux in an oil bath at 80 °C for 4 h with magnetic stirring. After the reaction was complete, the mixture was transferred to a separatory funnel for extraction and separation. The upper organic phase was extracted and washed three times with water. Finally, n-hexane was removed using a rotary evaporator to obtain a brown colloidal liquid, which was dried under vacuum for 12 h to obtain ferric oleate.

[0101] Preparation of cobalt oleate: 130 mg of CoCl2 was dissolved in a mixed solution consisting of 15 mL of deionized water and 15 mL of n-hexane. Then, 608 mg of sodium oleate was added, and the mixture was heated under reflux in an oil bath at 80 °C for 4 h with magnetic stirring. After the reaction was complete, the mixture was transferred to a separatory funnel for extraction and separation. The upper organic phase was extracted and washed three times with water. Finally, n-hexane was removed using a rotary evaporator to obtain a purple gelatinous liquid, which was dried under vacuum for 12 h. Subsequently, it was vacuum-stored after degassing to prevent oxidation of divalent cobalt, thus obtaining cobalt oleate.

[0102] Dissolve 18.66 mg of cobalt oleate in 1 mL of n-hexane, then dissolve 2.67 g of ferric oleate in a three-necked flask containing 15 mL of 1-octadecene, add the hexane solution of cobalt oleate to the flask, and then add 200 μL of oleic acid to obtain a mixed solution.

[0103] The mixed solution was heated to 120℃ and held for 30 min, with continuous evacuation during heating. After reaching the holding temperature, nitrogen gas was introduced and evacuation was repeated three times. Nitrogen gas was then introduced and the reaction continued for 30 min. The temperature was then increased to 200℃ and held for 30 min, and then increased to 310℃ and held for 10 h. After the reaction was completed, the solution was cooled to room temperature. The resulting solution was transferred to a 50 mL centrifuge tube, 1 mL of n-hexane was added, and the mixture was thoroughly mixed. Then, 5 mL of anhydrous ethanol was added, and the mixture was shaken for 1 min. The solution was centrifuged at 6000 rpm for 6 min, the supernatant was removed, and the precipitate was retained.

[0104] Repeat the following washing steps three times for the precipitate: add 5 mL of n-hexane and mix well; then add 5 mL of anhydrous ethanol and shake to mix for 1 min; centrifuge at 6000 rpm for 6 min and discard the supernatant.

[0105] The washed precipitate was redispersed in 5 mL of chloroform to maintain good dispersibility and ensure aqueous phase transfer. This yielded trace cobalt-doped magnetic nanoparticles (Co). 0.03 Fe 2.97 O4.

[0106] Example 4

[0107] A type of magnetic nanoparticle doped with trace amounts of cobalt (Co) 0.1 Fe 2.9 The preparation method of O4 includes the following steps:

[0108] Preparation of ferric oleate: 3.6 g of FeCl3·6H2O was dissolved in a mixed solution consisting of 15 mL of deionized water and 15 mL of n-hexane. Then, 12.2 g of sodium oleate was added, and the mixture was heated under reflux in an oil bath at 80 °C for 4 h with magnetic stirring. After the reaction was complete, the mixture was transferred to a separatory funnel for extraction and separation. The upper organic phase was extracted and washed three times with water. Finally, n-hexane was removed using a rotary evaporator to obtain a brown colloidal liquid, which was dried under vacuum for 12 h to obtain ferric oleate.

[0109] Preparation of cobalt oleate: 130 mg of CoCl2 was dissolved in a mixed solution consisting of 15 mL of deionized water and 15 mL of n-hexane. Then, 608 mg of sodium oleate was added, and the mixture was heated under reflux in an oil bath at 80 °C for 4 h with magnetic stirring. After the reaction was complete, the mixture was transferred to a separatory funnel for extraction and separation. The upper organic phase was extracted and washed three times with water. Finally, n-hexane was removed using a rotary evaporator to obtain a purple gelatinous liquid, which was dried under vacuum for 12 h. Subsequently, it was vacuum-stored after degassing to prevent oxidation of divalent cobalt, thus obtaining cobalt oleate.

[0110] Dissolve 62.2 mg of cobalt oleate in 1 mL of n-hexane, then dissolve 2.61 g of ferric oleate in a three-necked flask containing 15 mL of 1-octadecene, add the hexane solution of cobalt oleate to the flask, and then add 200 μL of oleic acid to obtain a mixed solution.

[0111] The mixed solution was heated to 120℃ and held for 30 min, with continuous evacuation during heating. After reaching the holding temperature, nitrogen gas was introduced and evacuation was repeated three times. Nitrogen gas was then introduced and the reaction continued for 30 min. The temperature was then increased to 200℃ and held for 30 min, and then increased to 310℃ and held for 10 h. After the reaction was completed, the solution was cooled to room temperature. The resulting solution was transferred to a 50 mL centrifuge tube, 1 mL of n-hexane was added, and the mixture was thoroughly mixed. Then, 5 mL of anhydrous ethanol was added, and the mixture was shaken for 1 min. The solution was centrifuged at 6000 rpm for 6 min, the supernatant was removed, and the precipitate was retained.

[0112] Repeat the following washing steps three times for the precipitate: add 5 mL of n-hexane and mix well; then add 5 mL of anhydrous ethanol and shake to mix for 1 min; centrifuge at 6000 rpm for 6 min and discard the supernatant.

[0113] The washed precipitate was redispersed in 5 mL of chloroform to maintain good dispersibility and ensure aqueous phase transfer. This yielded trace cobalt-doped magnetic nanoparticles (Co). 0.1 Fe 2.9 O4.

[0114] Comparative Example 1

[0115] A method for preparing cobalt-free cobalt-doped iron oxide magnetic nanoparticles (Fe3O4) includes the following steps:

[0116] Preparation of ferric oleate: 3.6 g of FeCl3·6H2O was dissolved in a mixed solution consisting of 15 mL of deionized water and 15 mL of n-hexane. Then, 12.2 g of sodium oleate was added, and the mixture was heated under reflux in an oil bath at 80 °C for 4 h with magnetic stirring. After the reaction was complete, the mixture was transferred to a separatory funnel for extraction and separation. The upper organic phase was extracted and washed three times with water. Finally, n-hexane was removed using a rotary evaporator to obtain a brown gelatinous liquid, which was then dried under vacuum for 12 h.

[0117] Dissolve 2.7 g of ferric oleate in a three-necked flask containing 15 mL of 1-octadecene, and then add 200 μL of oleic acid to obtain a mixed solution;

[0118] The mixed solution was heated to 120℃ and held for 30 min, with continuous evacuation during heating. After reaching the holding temperature, nitrogen gas was introduced and evacuation was repeated three times. Nitrogen gas was then introduced and the reaction continued for 30 min. The temperature was then increased to 200℃ and held for 30 min, and then increased to 310℃ and held for 10 h. After the reaction was completed, the solution was cooled to room temperature. The resulting solution was transferred to a 50 mL centrifuge tube, 1 mL of n-hexane was added, and the mixture was thoroughly mixed. Then, 5 mL of anhydrous ethanol was added, and the mixture was shaken for 1 min. The solution was centrifuged at 6000 rpm for 6 min, the supernatant was removed, and the precipitate was retained.

[0119] Repeat the following washing steps three times for the precipitate: add 5 mL of n-hexane and mix well; then add 5 mL of anhydrous ethanol and shake to mix for 1 min; centrifuge at 6000 rpm for 6 min and discard the supernatant.

[0120] The washed precipitate was redispersed in 5 mL of chloroform to maintain good dispersibility and ensure aqueous phase transfer. This yielded magnetic nanoparticles, Fe3O4.

[0121] Example 5

[0122] A method for functionalizing the surface of micro-cobalt-doped magnetic nanoparticles using genetically engineered macrophage membranes to enable their surface to specifically target prostate cancer includes the following steps:

[0123] Surface modification of trace cobalt-doped magnetic nanoparticles using maleic anhydride-1-octadecene (PMH):

[0124] Weigh 1 g of maleic anhydride-1-octadecene (PMH) and dissolve it in 5 mL of chloroform. Slowly add the trace amount of cobalt-doped magnetic nanoparticle chloroform solution provided in Example 1 dropwise to the PMH solution while continuously stirring magnetically. Continue stirring at room temperature for 4 h to ensure that PMH is fully coated on the surface of the oil-phase magnetic particles. After the reaction is complete, remove the chloroform from the solution using a rotary evaporator to obtain a black crystalline solid (PMH-modified magnetic particles).

[0125] Weigh 1 g of 4-dimethylaminopyridine (DMAP) and dissolve it in 10 mL of deionized water. Add the obtained black crystalline solid to the DMAP solution and sonicate in a water bath until the solid is completely dissolved. Then, centrifuge with deionized water at 16000 rpm for 2 h, and repeat the washing three times. Each time, discard the supernatant and redisperse the precipitate with deionized water to obtain surface-modified magnetic particles.

[0126] Extraction of the membrane from Raw264.7 macrophages exhibiting high affinity for prostate-specific membrane antigen (PSMA):

[0127] Genetically engineered macrophages were seeded into multiple 100 mm... 2 The cells were cultured in a petri dish at 37°C in a 5% CO2 incubator to allow them to adhere fully. Subsequently, all cells in the petri dish were washed off with phosphate-buffered saline (PBS), transferred to a 15 mL centrifuge tube, and centrifuged at 1700 rpm for 10 min to obtain the cell pellet.

[0128] A mixture of membrane protein extraction reagent A and protease inhibitor (PMSF) was added to the centrifuged cell pellet and placed on ice for 15 min. Subsequently, the pellet was rapidly frozen in liquid nitrogen and allowed to thaw naturally at room temperature; this freeze-thaw cycle was repeated 5 times. Afterward, the pellet was centrifuged at 1700 rpm for 10 min, and the supernatant was collected. Then, it was centrifuged again at 13000 rpm for 30 min to obtain the genetically engineered macrophage cell membrane. The volume ratio of membrane protein extraction reagent A to protease inhibitor was 20:1.

[0129] It should be noted that membrane protein extraction reagent A was purchased from Beyotime Biotechnology.

[0130] Among them, cell membrane protein and plasma protein extraction reagent A is a reagent with a solution volume ratio of 20:1 to PMSF.

[0131] Preparation of macrophage membrane-encapsulated magnetic particles: Macrophage membrane-encapsulated magnetic particles were prepared using an ultrasonic method and a physical extrusion method. The specific methods are as follows:

[0132] 200 µg of surface-modified magnetic particles were dissolved in deionized water, and 400 µL of macrophage membrane was dissolved in 1 mL of PBS. The two dispersions were then mixed in an ice bath and ultrasonically dispersed at 65 W for 30 min. The ultrasonic dispersion was then extruded through a 400 nm polycarbonate microporous membrane using a liposome extruder, and the extrusion was repeated 10 times. Finally, the mixture was centrifuged and washed 3 times to remove unbound cell membrane fragments and free magnetic particles, thus obtaining the macrophage membrane-encapsulated magnetic particles.

[0133] To illustrate the relevant properties of the magnetic nanoparticles provided by this invention, the accompanying drawings are provided.

[0134] Morphology characterization of magnetic nanoparticles: See Figure 1 As shown, the magnetic nanomaterials prepared in Examples 1-4 are magnetic nanoparticles with an octahedral shape and a cubic anti-spinel crystal structure, exhibiting high saturation magnetization and magnetic susceptibility, as well as moderate coercivity and remanent magnetization. Due to the excellent magnetism and moderate coercivity and relaxation time of these ferromagnetic nanoparticles, their response speed under the oscillating magnetic field excitation of the MPI system is moderate. Therefore, they exhibit sensitive imaging signals in low-frequency MPI imaging and excellent heat generation effects in high-frequency magnetocaloric excitation. The particle size of these trace cobalt-doped magnetic nanoparticles is 10-20 nm.

[0135] Characterization of the magnetic properties of magnetic nanoparticles: See Figure 2 The figures show the magnetization curves of the magnetic nanoparticles provided in Examples 1-4 and Fe3O4 provided in Comparative Example 1, including static magnetization tests and high-frequency relaxation tests. Figure 2 In this context, Co 0.05F is the magnetic nanoparticle provided in Example 1, Co 0.01F is the magnetic nanoparticle provided in Example 2, Co 0.03F is the magnetic nanoparticle provided in Example 3, and Co 0.1F is the magnetic nanoparticle provided in Example 4. Figure 2 It can be seen that the magnetic nanomaterials exhibit a saturation magnetization of 100-150 emu / g Fe and a coercivity of 5-100 mT under static vibration magnetometer testing.

[0136] See Figure 3 As shown, this is the test result of the spectral attenuation and relaxation time of the magnetic nanoparticles provided in Example 1. Figure 3 It can be seen that under a high-frequency alternating magnetic field (25 mT, 10 kHz), it exhibits relatively slow harmonic attenuation, with a relaxation time of 6.16 μs.

[0137] See Figure 4 As shown, the trace cobalt-doped magnetic nanoparticles Co provided in Example 1 are used. 0.05Fe 2.95 O4 and the magnetic nanoparticles provided in Comparative Example 1 were diluted with deionized water sequentially to iron concentrations of 0.2 mg / mL, 0.1 mg / mL, 0.05 mg / mL, and 0.025 mg / mL, respectively. The same concentration of the commercially available magnetic particle imaging tracer VivoTrax was also prepared, with 100 μL of each diluted nanoparticle in 200 μL PCR tubes. Scanning was then performed using a magnetic particle imaging system (Magnetic Insight). See [link to documentation]. Figure 4 It can be seen that the imaging signal intensity of trace cobalt-doped magnetic nanoparticles is about 7.4 times that of commercial tracers.

[0138] Characterization of the magnetocaloric effect of magnetic nanoparticles: See Figure 5 As shown, 100 μL of an aqueous solution of the trace cobalt-doped magnetic nanoparticles provided in Example 1, the magnetic nanoparticles provided in Comparative Example 1, and the commercially available magnetic particle VivoTrax was prepared and injected into a 500 μL centrifuge tube. The tube was then placed in the copper coil of a high-frequency magnetocalor SPG400K2, and an infrared thermal imaging camera was placed above it to record temperature changes. Subsequently, the aqueous solution of 1 mg / mL of trace cobalt-doped magnetic nanoparticles was held under an alternating magnetic field (power 2 kW, frequency 360 kHz) for 150 s, and then cooled to room temperature. This heating and cooling cycle was repeated three times, and the temperature results were recorded using an infrared thermal imaging camera. Figure 5 It was found that trace amounts of cobalt-doped magnetic nanoparticles rapidly heated to 45°C within 150 seconds, while commercially available magnetic particles, VivoTrax, exhibited a temperature change of less than 5°C. (See also...) Figure 6 As shown, the magnetocaloric stability of the trace cobalt-doped magnetic nanoparticles provided in Example 1 was tested. Figure 6 It can be seen that during the four heating cycles, the trace cobalt-doped magnetic nanoparticles maintained a stable heating rate and exhibited good thermal stability.

[0139] Based on the characterization results of the magnetocaloric effect, see Figure 7 The figure shows the calculated magnetocaloric specific absorptivity (SAR) of the trace cobalt-doped magnetic nanoparticles provided in Example 1, the magnetic nanoparticles provided in Comparative Example 1, and commercial magnetic particles. The SAR value was calculated using the following formula after testing the magnetocaloric properties of the samples:

[0140]

[0141] In the formula, ΔT is the heat capacity of the medium; ΔT is the temperature change; Δt is the time change; m v The mass of the suspension; This represents the iron content of the magnetic particles in the suspension. Figure 7It can be seen that the specific absorption rate of the trace cobalt-doped magnetic nanoparticles calculated according to the above formula is about 12 times that of the commercial magnetic particles VivoTrax.

[0142] See Figure 8 As shown in Example 5, the surface of micro-cobalt-doped magnetic nanoparticles was functionalized by using genetically engineered macrophage membranes, giving the surface the ability to specifically target prostate cancer. Figure 8 It can be seen that the surface of micro-cobalt-doped magnetic nanoparticles is uniformly covered by cell membranes.

[0143] Tumor imaging performance test: The magnetic particles encapsulated in macrophage membranes provided in Example 5 were used for imaging experiments in tumor-bearing mice. The magnetic particles (1 mg Fe / mL, 200 μL) modified with genetically engineered cell membranes were injected into tumor-bearing nude mice via the tail vein. After injection, the mice were anesthetized with isoflurane and placed in an MPI imaging system. MPI scans were performed at specific time points 48 h post-injection to detect the MPI signal intensity at various sites within the mice. Figure 9 As shown. Figure 9 It can be seen that the surface-functionalized magnetic particles exhibited a strong MPI signal at the tumor site 48 hours after injection, successfully marking the location of the tumor.

[0144] Tumor magnetothermal performance test: 20 μL of macrophage membrane-encapsulated magnetic particles (provided in Example 5) at a concentration of 5 mg / mL were injected into the tumors of mice in the experimental group. The injection process was slow to avoid drug extravasation. After injection, both groups of mice were placed in the copper coil of a high-frequency magnetothermal device for 10 minutes for magnetothermal therapy at a power of 2 kW. The infrared temperature monitoring results after 10 minutes are as follows: Figure 10 As shown. Figure 10 It is known that after injecting the magnetic nanomaterial modified with genetically engineered cell membranes, the temperature of the tumor area reached 47°C within 10 minutes, and this heating effect met the requirements for tumor ablation.

[0145] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing trace amounts of cobalt-doped magnetic nanoparticles, characterized in that, Includes the following steps: Preparation of cobalt oleate and iron oleate; Cobalt oleate was dissolved in n-hexane to obtain a cobalt oleate solution; iron oleate was dissolved in 1-octadecene, then the cobalt oleate solution was added, followed by the addition of oleic acid to obtain a mixed solution; The mixed solution was heated to 100-120℃ and held for 25-35 min, during which gas was continuously evacuated. After reaching the holding temperature, nitrogen gas was introduced and gas was evacuated again, which was repeated 2-3 times. Then nitrogen gas was introduced and the reaction continued for 25-35 min. The temperature was then increased to 190-210℃ and held for 25-35 min. The temperature was then increased to 310-320℃ and held for 10-20 h. After the reaction was completed, the solution was cooled to room temperature to obtain trace cobalt-doped magnetic nanoparticles. When preparing the mixed solution, the molar ratio of cobalt oleate to iron oleate is (0.001~1):(29~30). After cooling to room temperature, it also includes: After the reaction is complete, transfer the solution to a centrifuge tube, add n-hexane, mix thoroughly, then add anhydrous ethanol, shake to mix, and then centrifuge to remove the supernatant and retain the precipitate. Repeat the following washing steps three times for the precipitate: add n-hexane, mix well, then add anhydrous ethanol, shake to mix well; centrifuge at 5000~8000 rpm for 5~10 min, and discard the supernatant. The cobalt oleate or iron oleate is prepared according to the following steps: Cobalt or iron salts are uniformly dispersed in a mixed solvent of water and n-hexane, followed by the addition of sodium oleate. After refluxing at 75-85°C for 3-5 hours, the reactants are extracted and separated. The upper organic phase is extracted, washed, and dried to obtain cobalt oleate or iron oleate. The molar ratio of the cobalt salt or iron salt to sodium oleate is 1:2~3; The magnetic nanoparticles are cobalt ferrite with the chemical formula Co. x Fe 3-x O4, where 0 < x ≤ 0.1; Cobalt ions in the cobalt ferrite are doped at octahedral sites on the crystal lattice surface; The magnetic nanoparticles have a magnetic susceptibility of 100-150 emu·g. -1 Fe, relaxation time is 0-100 μs; The magnetic nanoparticles have a particle size of 10-20 nm.

2. A trace amount of cobalt-doped magnetic nanoparticles prepared by the method of claim 1.

3. The application of the trace cobalt-doped magnetic nanoparticles of claim 2 in the preparation of diagnostic or therapeutic tumor drugs, characterized in that, In the preparation of diagnostic or therapeutic tumor drugs, the surface of magnetic nanoparticles is sequentially modified with a biocompatible ligand and a targeting molecule; wherein the biocompatible ligand is maleic anhydride-1-octadecene; and the targeting molecule is Raw264.7 macrophage membrane with affinity for prostate-specific membrane antigen.

4. A method for preparing diagnostic or therapeutic tumor drugs using the trace cobalt-doped magnetic nanoparticles as described in claim 2, characterized in that, Includes the following steps: Macrophage membranes were extracted and dispersed in PBS, and then mixed with trace amounts of cobalt-doped magnetic nanoparticles dispersed in an aqueous solvent to obtain a mixture. After sonicating the mixture in a cell disruptor for 20-40 minutes, the mixture is then circulated and extruded 8-10 times through an extruder to obtain micro-cobalt-doped magnetic nanoparticles with cell membranes modified on the surface.

5. The application of the trace cobalt-doped magnetic nanoparticles of claim 2 in magnetic particle imaging probes or magnetothermal therapy agents.

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