Chemically modified nanodiamond particles, their manufacturing method, and MRI contrast agent using same

Abstract

To provide a chemically modified nano diamond particle having high dispersibility.SOLUTION: A chemically modified nano diamond particle has a complex comprising a ligand formed by the bonding between a nano diamond particle having an introduced carboxyl group, and a chelating agent, and a metal ion.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present disclosure relates to chemically modified nanodiamond particles, a method for producing the same, and an MRI contrast agent using the same. [Background technology]

[0002] Nanodiamond particles have low cytotoxicity and high biocompatibility, and therefore research into their medical applications is being actively conducted. One example is the development of a contrast agent for magnetic resonance imaging (MRI) using nanodiamond particles (Patent Document 1).

[0003] The size of an MRI contrast agent required to image the lymphatic system is thought to be 3 nm or more. A conventional MRI contrast agent known is Gd-DTPA, which is a compound of gadolinium (Gd) ions and diethylenetriaminepentaacetic acid (DTPA), but this Gd-DTPA is smaller than this size and cannot image the lymphatic system.

[0004] To solve this problem, in a previous study, Gd-DTPA-ND was developed by combining nanodiamond particles (ND) with DTPA and forming a complex with Gd ions (Non-Patent Document 1). Since the primary particle diameter of Gd-DTPA-ND is about 5 nm, it was thought that if it is dispersed in plasma, it will be taken up by lymphatic vessels in the body, making it possible to perform MRI imaging of the entire lymphatic system, which had been difficult until now. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent Publication No. 2008-079824 [Non-patent literature]

[0006] [Non-Patent Document 1] Nakamura T, Ohana T, Yabuno H, Kasai R, Suzuki T, Hasebe T: Simple fabrication of GD(3)-DTPA-nanodiamond particles by chemical modification for use as magnetic resonance imaging(MRI) contrast agent. Appl Phys Express 6: 015001, 2013 Summary of the Invention [Problem to be solved by the invention]

[0007] However, it was found that this Gd-DTPA-ND aggregates to the microscale in water and plasma, exceeding the size required for subsequent excretion by the kidney.

[0008] In one aspect of the present disclosure, the development of more dispersible nanodiamond particles was sought. [Means for solving the problem]

[0009] One aspect of the present disclosure is a chemically modified nanodiamond particle, which comprises a complex consisting of a ligand formed by bonding between a nanodiamond particle having a carboxyl group introduced therein and a chelating agent, and a metal ion.

[0010] Additionally, in one aspect of the present disclosure, the metal ion may be a gadolinium ion. In one embodiment of the present disclosure, the chelating agent may be a compound having a carboxyl group.

[0011] Also, in one aspect of the present disclosure, the chelating agent may be diethylenetriaminepentaacetic acid. Also, in one aspect of the present disclosure, the chelating agent may be 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetate.

[0012] By using the above-mentioned chelating agent, it is possible to obtain chemically modified nanodiamond particles with higher dispersibility than conventional ones due to the carboxyl group, which is a hydrophilic group, introduced into the nanodiamond particles.

[0013] Also, one aspect of the present disclosure is an MRI contrast agent comprising the above-mentioned chemically modified nanodiamond particles. According to this configuration, good contrast effect can be achieved by using a low concentration of nanodiamond particles.

[0014] Also, one aspect of the present disclosure is a method for producing chemically modified nanodiamond particles, in which a carboxyl group is introduced into the nanodiamond particles, which is combined with a chelating agent to obtain a precursor, and the precursor is complexed with a metal ion.

[0015] In one embodiment of the present disclosure, the precursor may be stirred and then complexed with a metal ion. Additionally, in one aspect of the present disclosure, the metal ion may be a gadolinium ion.

[0016] Additionally, in one aspect of the present disclosure, the chelating agent may be diethylenetriaminepentaacetic acid or 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetate.

[0017] This manufacturing method makes it possible to obtain chemically modified nanodiamond particles that are more dispersible than conventional methods. [Brief description of the drawings]

[0018] [Figure 1] These are the spectra analyzed by a Fourier transform infrared spectrophotometer (hereinafter, FTIR) for CND, DTPA-CND, and Gd-DTPA-CND. [Diagram 2] The analysis spectra of CND, DTPA-CND, and Gd-DTPA-CND by X-ray photoelectron spectroscopy (hereinafter, XPS). [Diagram 3]These are images of Gd-DTPA-ND and Gd-DTPA-CND in water obtained by a transmission electron microscope (hereinafter, TEM). [Figure 4] 1 is a graph showing the particle size distribution of Gd-DTPA-ND and Gd-DTPA-CND in water, measured by dynamic light scattering (hereinafter, DLS). [Diagram 5] These are MRI images of Gd-DTPA (Gd concentration 0.75 mM), Gd-DTPA-CND (Gd concentration 0.05 mM), and Gd-DTPA (Gd concentration 1.00 mM) in water. [Figure 6] TEM images of Gd-DTPA-CND in plasma. [Figure 7] These are MRI images of plasma and Gd-DTPA-CND (Gd concentration 0.25 mM) in plasma. [Figure 8] MRI images of Gd-DTPA-CND in the rat vasculature. [Figure 9] FTIR analysis spectra of CND, DOTA-CND, and Gd-DOTA-CND. [Figure 10] TEM images of Gd-DOTA-CNDs in water. [Figure 11] 1 is a graph showing the particle size distribution of CND, DOTA-CND, and Gd-DOTA-CND in water measured by DLS. [Figure 12] MRI images of Gd-DOTA-CNDs (Gd concentration 0.05 mM) in water. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] Hereinafter, exemplary embodiments of the present disclosure will be described with reference to the drawings. <Chemically modified nano diamond particles> The chemically modified nanodiamond particles of the present disclosure include a complex consisting of a ligand formed by binding a chelating agent with a nanodiamond particle (CND) having a carboxyl group introduced therein and a metal ion. The chemically modified nanodiamond particles of the present disclosure may be represented by the following schematic diagrams [Chemical formula 1] and [Chemical formula 2].

[0020] [ka]

[0021] [ka] The chemically modified nanodiamond particles disclosed herein are less likely to aggregate in water and plasma because highly hydrophilic carboxyl groups have been introduced into the nanodiamond particles.

[0022] Nanodiamond particles tend to aggregate and form micro-sized aggregates when present alone in water and blood plasma. On the other hand, when using nanodiamond particles as an MRI contrast agent (especially when using them as an MRI contrast agent for the lymphatic system), the nanodiamond particles need to have a small particle size that can pass through lymphatic vessels and blood vessels. When nanodiamond particles aggregate to a micro-sized size, the aggregated nanodiamond particles cannot pass smoothly through lymphatic vessels and blood vessels, and cannot be used as an MRI contrast agent for lymphatic and vascular system imaging.

[0023] In the present disclosure, carboxyl groups are introduced into nanodiamond particles to make the surface of nanodiamond particles hydrophilic. Therefore, nanodiamond particles are dispersed in water and blood plasma in the form of primary particles with a size of, for example, about several nm, and these particles can be prevented from agglomerating. In other words, the chemically modified nanodiamond particles of the present disclosure have higher dispersibility in water and blood plasma than chemically modified nanodiamond particles having nanodiamond particles without carboxyl groups.

[0024] Such nanodiamond particles can pass through lymphatic and blood vessels and can be suitably used as an MRI contrast agent for imaging the lymphatic and vascular systems. The chemically modified nanodiamond particles of the present disclosure preferably have a particle diameter of 3-10 nm.If the particle diameter is less than 3 nm, the chemically modified nanodiamond particles may not be taken up into lymphatic vessels.In addition, if the particle diameter is more than 10 nm, the chemically modified nanodiamond particles may not be easily excreted from the kidney to the bladder.

[0025] The metal ion used in the chemically modified nanodiamond particle of the present disclosure can include paramagnetic metal ions such as gadolinium (Gd) ion, manganese ion, chromium ion, copper ion, iron ion, praseodymium ion, neodymium ion, samarium ion, terbium ion, ytterbium ion, dysprosium ion, holmium ion, erbium ion, etc. Among them, gadolinium ion or manganese ion is preferred, and gadolinium ion is more preferred. In this embodiment, gadolinium ion is used as metal ion.

[0026] The chelating agent used in the chemically modified nanodiamond particles of the present disclosure may be a compound having a carboxyl group. Specifically, diethylenetriaminepentaacetic acid (DTPA), 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetate (DOTA), diethylenetriaminepentaacetic acid-butyl methacrylate (DTPA-BMA), DTPA anhydride, 1,4,7,10-tetraazacyclododecane-1,4,7-triacetate (DO3A), 2-hydroxypropyl-1,4,7,10-tetraazacyclododecane-1,4,7-triacetate (HP-DO3A), etc. are listed. Among these, DTPA is preferably used from the viewpoint of less influence on the human body and good dispersibility, and DOTA is preferably used from the viewpoint of stable chelation. In this embodiment, DTPA and DOTA are used as chelating agents.

[0027] <Method for preparing chemically modified nanodiamond particles> The chemically modified nanodiamond particles of the present disclosure are prepared by introducing carboxyl groups onto nanodiamond particles, combining the nanodiamond particles with a chelating agent to obtain a precursor, and complexing the precursor with metal ions.

[0028] Here, the introduction of carboxyl groups into nanodiamond particles may be carried out by subjecting the nanodiamond particles to an oxidation treatment, thereby modifying some or all of the hydrophobic groups (e.g., hydrocarbon groups) present on the surface of the nanodiamond particles with carboxyl groups.

[0029] Specifically, the oxidation treatment of the nanodiamond particles may be carried out by contacting the nanodiamond particles with an acid solution. The acid solution may be, for example, a solution of sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, acetic acid, etc. The reaction temperature of the oxidation treatment is preferably 200°C to 250°C, and the concentration of the acid solution is preferably 95% to 100%.

[0030] The amount of carboxyl groups introduced into the nanodiamond particles may be 1-100, or even 3-50 per nanodiamond particle. In addition, it is preferable that the carboxyl groups are uniformly introduced onto the surface of the nanodiamond particles. This gives the surface of the nanodiamond particles a uniform affinity to water or plasma, and the chemically modified nanodiamond particles can be more effectively dispersed in water or plasma.

[0031] In addition, in the preparation process of the present disclosure, a precursor is generated in which the nanodiamond particles having carboxyl groups are bonded to the chelating agent. The bond between the nanodiamond particles and the chelating agent may be a covalent bond, and more preferably, a direct bond without a linker. Specifically, the bond may be a condensation bond between the hydroxyl group of the nanodiamond particles and the carboxyl group of the chelating agent. The hydroxyl group of the nanodiamond particles may be formed, for example, by heating the nanodiamond particle surface with heat generated during the nanodiamond particle manufacturing process by explosion method or the like, and oxidizing the CH group on the particle surface.

[0032] For example, thionyl chloride can be added to the dichloromethane suspension containing nanodiamond particles and chelating agent to bond the chelating agent to the nanodiamond particles. The mixing ratio of the chelating agent and nanodiamond particles contained in the dichloromethane suspension is preferably 100:10-100, more preferably 100:15-50.

[0033] The concentration of the nanodiamond particles in the dichloromethane suspension is preferably 10 to 15 g / L, and the concentration of the chelating agent in the dichloromethane suspension is preferably about 50 g / L.

[0034] The precursor is then complexed with a metal ion. When the precursor is complexed with a metal ion, the compounding ratio of the precursor to the metal ion is preferably 100:10-100, more preferably 100:15-50.

[0035] As described above, by binding the nanodiamond to a chelating agent prior to complex formation, the detachment of metal ions can be reduced. In addition, in order to further improve the dispersibility of chemically modified nanodiamond particles, the solution containing the precursor may be stirred before the precursor is complexed with metal ions. Also, the solution containing the final product obtained may be stirred after the precursor is complexed with metal ions. Stirring may be performed, for example, by ultrasonic waves and / or a stirrer.

[0036] [Example 1] [1-1. Preparation of chemically modified nanodiamond particles] The preparation method for the chemically modified nanodiamond particles of Example 1 is shown below.

[0037] First, the nanodiamond particles were subjected to an oxidation treatment to uniformly modify the surface of the nanodiamond particles with hydrophilic carboxyl groups, to prepare CNDs as shown in the following schematic diagram [Chemical formula 3]. The specific conditions for the oxidation treatment were a reaction temperature of 200°C and 95% nitric acid.

[0038] [ka] In addition, in the above schematic diagram [Chemical Formula 3], the number of carboxyl groups on the surface of the nanodiamond particle is merely an example and is not limited to this.

[0039] Next, 300 mg of CND and 1 g of DTPA were dissolved in dichloromethane (CH 2 Cl 2 ) and mixed in 20 mL of thionyl chloride (SOCl 2 2.5 mL of CH was added dropwise, and the mixture was refluxed for 5 hours. This resulted in dehydration condensation of CND and DTPA. This reaction (dehydration condensation) was carried out at 40°C. 2 Cl 2 The reaction solution was washed with SOCl. 2 The reaction solution was then washed with an aqueous solution of sodium hydroxide (NaOH) to remove excess CH 2 Cl 2 Then, methanol (CH 3The excess NaOH was removed by washing with NaOH (OH). Finally, the reaction solution was washed with water to obtain DTPA-CND, which is represented by the following schematic diagram [Chemical formula 4].

[0040] [ka] In addition, in the above schematic diagram [Chemical Formula 4], the number of carboxyl groups on the surface of the nanodiamond particle is merely an example and is not limited to this.

[0041] Then, gadolinium chloride (III) (Gd Cl) was added to 2 mL of the DTPA-CND solution. 3 ) solution was dropped to adjust the Gd concentration (the DTPA-CND concentration in the DTPA-CND solution was 6 g / L, and the dropped Gd Cl 3 Gd Cl in aqueous solution 3 The concentration was 1 g / L.) As a result, the final product, Gd-DTPA-CND, was obtained, as shown in the following schematic diagram [Chemical formula 5].

[0042] [ka] In addition, in the above schematic diagram [Chemical Formula 5], the number of carboxyl groups on the surface of the nanodiamond particle is merely an example and is not limited to this.

[0043] [1-2. Structural analysis and performance evaluation] (1)Chemical structure analysis The chemical structure of the prepared Gd-DTPA-CND (Example 1) was analyzed using FTIR. For comparison, the chemical structure of CND and DTPA-CND was also analyzed using FTIR. The measurement range of FTIR was 500-4000 cm wavenumber. -1 The resolution is 4 cm. -1 As shown in Figure 1, the analysis spectrum of Gd-DTPA-CND shows that the wavenumber range is 1500 to 1600 cm -1 A peak specific to the carbonyl group appeared at wavenumbers of 3000 to 3500 cm -1The peak of the hydroxyl group of CND was smaller than that of CND. This is considered to be due to dehydration condensation between the hydroxyl group of CND and the carboxyl group of DTPA.

[0044] In addition, the chemical composition analysis of Gd-DTPA-CND was performed using XPS. Furthermore, the chemical composition analysis of CND and DTPA-CND was also performed using XPS. Gd-DTPA-CND, CND, and DTPA-CND were freeze-dried for 48 hours and then subjected to XPS measurement. Monochromatic MgKa or AlKa rays were used as the X-ray source. The measurement time was 30 minutes. The measurement range was 0 eV-700 eV.

[0045] As shown in Figure 2, in the analysis spectrum of Gd-DTPA-CND, a peak specific to Gd was present near the binding energy of 140 eV. On the other hand, in the analysis spectrum of CND and DTPA-CND, no such peak was present.

[0046] From the above results, in the case of Gd-DTPA-CND, the CND was surface-modified with DTPA, and the DTPA-CND and Gd 3+ It was confirmed that a complex was formed. (2) Evaluation of dispersibility in water TEM observation was performed to evaluate the dispersibility of Gd-DTPA-CND in water. The acceleration voltage was 120 kV, and the magnification was 125,000 times. Figure 3 shows TEM image 1 (concentration in water 1 g / L) of Gd-DTPA-ND in which carboxyl groups were not introduced to nanodiamond particles, and TEM image 2 (concentration in water 1 g / L) of Gd-DTPA-CND in Example 1 in which carboxyl groups were introduced to nanodiamond particles. As shown in image 1, aggregation of Gd-DTPA-ND was observed in water. On the other hand, as shown in image 2, due to the modification of the carboxyl groups on the surface of the nanodiamond particles, Gd-DTPA-CND was dispersed in water without aggregation.

[0047] FIG. 4 shows the results of measuring the particle sizes of Gd-DTPA-ND and Gd-DTPA-CND in water by DLS. The measurement conditions were room temperature, 50 trials (3 repetitions), and a 10MW He-Ne laser. As shown in FIG. 4, Gd-DTPA-ND (concentration in water: 1 g / L) formed aggregates with an average particle size of about 1000 nm in water. On the other hand, the average particle size of Gd-DTPA-CND (concentration in water: 1 g / L) was 4.3 nm.

[0048] (3) Evaluation of MRI visibility Next, MRI imaging of Gd-DTPA-CND (Example 1) and Gd-DTPA (Comparative Example) was performed. The imaging conditions were 1.5T MRI (T-1 weighted, repetition time (TR): 580 ms, echo time (TE): 12 ms). The concentration of Gd-DTPA-CND (Example 1) and Gd-DTPA (Comparative Example) was changed by adjusting the amount of water added. The suspension of each concentration was placed in a 6 cc cylindrical screw tube, and its cross section was imaged.

[0049] An MRI image 3 of Gd-DTPA (Gd concentration 0.75 mM) in water, an MRI image 4 of Gd-DTPA-CND (Gd concentration 0.05 mM), and an MRI image 5 of Gd-DTPA (Gd concentration 1.00 mM) were obtained. These images 3 to 5 were compared (see FIG. 5). In addition, to compare the brightness of the center of each image 3 to 5, enlarged images 6 to 8 of the center of the image are shown above each image 3 to 5. It was confirmed that the enlarged image 7 corresponding to Gd-DTPA-CND (Gd concentration 0.05 mM) is brighter than the enlarged image 6 corresponding to Gd-DTPA (Gd concentration 0.75 mM) and darker than the enlarged image 8 corresponding to Gd-DTPA (Gd concentration 1.00 mM). From this, it was confirmed that Gd-DTPA-CND has the same contrast effect as Gd-DTPA by combining Gd-DTPA with one nanodiamond particle, at a Gd concentration about 1 / 15 to 1 / 20 of that of Gd-DTPA. Therefore, it is considered that Gd-DTPA-CND can be administered in a smaller amount to the body than Gd-DTPA.

[0050] (4) Evaluation of dispersibility and visibility in plasma Fig. 6 shows a TEM image 9 of the Gd-DTPA-CND of Example 1 in plasma. The plasma was obtained by centrifuging adult male human blood at 3500 rpm for 5 minutes. It was found that the Gd-DTPA-CND of Example 1 maintained a high dispersibility even in plasma, similar to the state of Gd-DTPA-CND in water shown in TEM image 2.

[0051] In addition, MRI imaging of Gd-DTPA-CND in plasma was performed (see FIG. 7). Then, MRI image 10 of plasma was compared with image 11 of Gd-DTPA-CND (Gd concentration 0.25 mM) in plasma. This showed that Gd-DTPA-CND has high MRI visibility in plasma as well as in water.

[0052] (5) MRI imaging and renal excretion in the rat vasculature Next, MRI imaging was performed on rats to which the Gd-DTPA-CND of Example 1 was intravenously administered. Figure 8 shows an MRI imaging image of the rat vascular system.

[0053] 0.3cc of Gd-DTPA-CND suspension (Gd concentration: 50mM) was injected into the tail vein of the rat. After that, MRI images of the entire rat were acquired every minute for 10 minutes with 3.0T MRI. The imaging conditions were set to a repetition time (TR) of 4.5942ms and an echo time (TE) of 1.967ms. MRI image 12 is an MRI image of the rat before the injection of the Gd-DTPA-CND suspension. Meanwhile, MRI image 13 is an MRI image of the rat immediately after the injection of the Gd-DTPA-CND suspension, depicting the rat's vascular system.

[0054] Moreover, the MRI image 14 shows an MRI image of a rat 10 minutes after 0.3 cc of Gd-DTPA-CND suspension was injected. The imaging conditions were set to a repetition time (TR) of 4.6455 ms and an echo time (TE) of 2.005 ms. In the MRI image 14, the rat's bladder was visualized as white. Therefore, it was found that Gd-DTPA-CND was filtered by the kidney and excreted into the bladder. Therefore, it was shown that Gd-DTPA-CND in the present disclosure is highly dispersible in plasma, so that it can be MRI-imaging-enabled in the vascular system of a rat, and has renal excretion after MRI-imaging. Furthermore, since Gd-DTPA-CND in the present disclosure is highly dispersible in plasma, it is estimated that it is similarly highly dispersible in the lymphatic system.

[0055] In general, contrast agents are excreted in the biliary system as well as through the kidney (i.e., urine), but contrast agents that are excreted in urine are generally easier to use clinically. Gd-DTPA-CND is extremely useful clinically because it is excreted in the kidney as described above.

[0056] In addition, MRI imaging of the rat vascular system was not possible with Gd-DTPA-ND without a carboxyl group (not shown). This is thought to be because Gd-DTPA-ND aggregated in water and increased in particle size, preventing it from passing through the injection needle.

[0057] [Example 2] [2-1. Preparation of chemically modified nanodiamond particles] The preparation method for the chemically modified nanodiamond particles of Example 2 is as follows: Example 2 uses DOTA instead of DTPA as the chelating agent.

[0058] The same CND (300 mg) and DOTA (1 g) used in Example 1 were 2 Cl 2 Mix in 20 mL of SOCl 22.5 mL of CND was added dropwise, and the mixture was refluxed for 5 hours. This resulted in dehydration condensation of CND and DTPA. This reaction (dehydration condensation) was carried out at 40°C. Then, CH 2 Cl 2 The reaction solution was washed with SOCl. 2 The reaction solution was washed with an aqueous NaOH solution to remove excess CH 2 Cl 2 Remove and CH 3 The excess NaOH was removed by washing with OH. Finally, the reaction solution was washed with water to obtain the DOTA-CND aqueous solution shown in the following schematic diagram [Chemical formula 6].

[0059] [ka] In addition, in the above schematic diagram [Chemical Formula 6], the number of carboxyl groups on the surface of the nanodiamond particle is merely an example and is not limited to this.

[0060] Next, 7 ml of zirconia beads (diameter 0.3 mm) were added to 3 ml of water containing an arbitrary amount of DOTA-CND aggregates, and the mixture was stirred for 10 minutes with an ultrasonic homogenizer to completely disperse the DOTA-CND.

[0061] Then, for 2 mL of DOTA-CND solution, Gd Cl 3 The Gd concentration was adjusted by dropping 1 mL of the aqueous solution. (The DOTA-CND concentration in the DOTA-CND aqueous solution was 6 g / L, and the amount of Gd Cl dropped was 1 mL.) 3 Gd Cl in aqueous solution 3 The concentration was 1 g / L.) This resulted in the final product, Gd-DOTA-CND, which is represented by the following schematic diagram [Chemical formula 7].

[0062] [ka] In addition, in the above schematic diagram [Chemical Formula 7], the number of carboxyl groups on the surface of the nanodiamond particle is merely an example and is not limited to this.

[0063] [2-2. Structural analysis and performance evaluation] (1)Chemical structure analysis The chemical structure of the prepared Gd-DOTA-CND (Example 2) was analyzed using FTIR. For comparison, the chemical structure of CND and DOTA-CND was also analyzed using FTIR. The measurement range of FTIR was 500-4000 cm wavenumber. -1 The resolution is 4 cm. -1 As shown in Figure 9, in the analysis spectrum of Gd-DOTA-CND, the wave number of 1000 cm -1 Peaks specific to the CO bond and CN bond derived from DOTA appeared around wavenumber 3000. -1 The peak of the hydroxyl group in the vicinity was smaller than that of CND. This is thought to be due to dehydration condensation between the hydroxyl group of CND and the carboxyl group of DOTA.

[0064] (2) Evaluation of dispersibility in water TEM observation was performed to evaluate the dispersibility of Gd-DOTA-CND of Example 2 in water. The acceleration voltage was 120 kV, and the magnification was 125,000 times. As shown in the image 15 of Gd-DOTA-CND (concentration in water 1 g / L) in Figure 10, Gd-DOTA-CND was dispersed in water due to the modification of many carboxyl groups on the nanodiamond surface.

[0065] FIG. 11 shows the results of measuring the particle diameters of Gd-DOTA-CND (Example 2) in water, and CND and DOTA-CND as comparative examples, by DLS. The measurement conditions were room temperature, 50 trials (3 repetitions), and a 10MW He-Ne laser. As shown in FIG. 11, the average particle diameter of Gd-DOTA-CND (concentration in water: 1 g / L) was 6.8 nm. The average particle diameter of CND (concentration in water: 1 g / L) was 2.7 nm, and the average particle diameter of DOTA-CND (concentration in water: 1 g / L) was 5.8 nm.

[0066] Therefore, it was found that the Gd-DOTA-CND of Example 2 has high dispersibility in water. (3) Evaluation of MRI visibility Next, MRI imaging of Gd-DOTA-CND (Example 2) was performed. The imaging conditions were 1.5T MRI (T-1 weighted, repetition time (TR): 580 ms, echo time (TE): 12 ms). The concentration of Gd-DOTA-CND (Example 2) was changed by adjusting the amount of water added. This suspension was placed in a 6 cc cylindrical screw tube, and its cross section was imaged. Then, an MRI imaging image 16 of Gd-DOTA-CND (Gd concentration 0.05 mM) of Example 2 in water was obtained (see FIG. 12).

[0067] The MRI image 16 was depicted brightly, and it was confirmed that it was of similar brightness to the MRI image 4 of Gd-DTPA-CND (Gd concentration 0.05 mM) of Example 1 in Figure 5, which was taken under the same imaging conditions.

[0068] From this, it was considered that Gd-DOTA-CND, like Gd-DTPA-CND, has the same contrast effect as existing MRI contrast agents at a low Gd concentration. [3. Effects] According to the examples detailed above, a precursor formed by bonding nanodiamond particles having carboxyl groups introduced therein with a chelating agent (DTPA, DOTA) is complexed with Gd ions, thereby obtaining chemically modified nanodiamond particles, which are nanodiamond particles with higher dispersibility than conventional nanodiamond particles.

[0069] Furthermore, in water and plasma, the chemically modified nanodiamond particles of the present disclosure have good MRI visibility and can exhibit good contrast effects even when used at low concentrations. Furthermore, the chemically modified nanodiamond particles disclosed herein enable MRI imaging in the vasculature of rats and are excreted through the kidney.

[0070] [4. Other embodiments] Although the embodiments of the present disclosure have been described above, the present disclosure is not limited to the above-described embodiments and can be implemented in various modified forms. The function of one component in each of the above embodiments may be shared by multiple components, or the function of multiple components may be performed by one component. Also, a part of the configuration of each of the above embodiments may be omitted. Also, at least a part of the configuration of each of the above embodiments may be added to, replaced with, or the like for the configuration of another of the above embodiments. Note that all aspects included in the technical idea specified by the wording described in the claims are embodiments of the present disclosure. [Explanation of symbols]

[0071] 1, 2, 9, 15…TEM images, 3–8, 10–14, 16…MRI images.

Claims

1. A chemically modified nanodiamond particle comprising a complex consisting of a ligand formed by bonding between a nanodiamond particle having an introduced carboxyl group and a chelating agent, and a metal ion, wherein the particle diameter of the chemically modified nanodiamond particle is 3 to 10 nm.

2. The chemically modified nanodiamond particles of claim 1, wherein the metal ion is a gadolinium ion.

3. The chemically modified nanodiamond particles according to claim 1 or claim 2, wherein the chelating agent is a compound having a carboxyl group.

4. The chemically modified nanodiamond particles of any one of claims 1 to 3, wherein the chelating agent is diethylenetriaminepentaacetic acid.

5. The chemically modified nanodiamond particles according to any one of claims 1 to 3, wherein the chelating agent is 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetate.

6. 6. An MRI contrast agent comprising the chemically modified nanodiamond particles of any one of claims 1 to 5.

7. A method for producing chemically modified nanodiamond particles, comprising introducing a carboxyl group into nanodiamond particles, combining the nanodiamond particles with a chelating agent to obtain a precursor, and complexing the precursor with a metal ion, wherein the particle diameter of the chemically modified nanodiamond particles is 3 to 10 nm.

8. The method for producing chemically modified nanodiamond particles according to claim 7, wherein the precursor is stirred and then complexed with the metal ions.

9. The method for producing chemically modified nanodiamond particles according to claim 7 or claim 8, wherein the metal ion is a gadolinium ion.

10. The method for producing chemically modified nanodiamond particles according to claim 8 or claim 9, wherein the chelating agent is diethylenetriaminepentaacetic acid or 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetate.

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