CN112539853B - Magnetic nanoparticle temperature measurement method based on electron paramagnetic resonance - Google Patents
Magnetic nanoparticle temperature measurement method based on electron paramagnetic resonance Download PDFInfo
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Abstract
The invention discloses a magnetic nanoparticle temperature measurement method based on electron paramagnetic resonance, and belongs to the technical field of nano material testing. The invention utilizes electron paramagnetic resonance equipment to measure the temperature by measuring the change of g factor of the resonance spectrum of the magnetic nanoparticles; specifically, magnetic nanoparticles have superparamagnetism, and the electron paramagnetic resonance spectrum shape of the magnetic nanoparticles is related to particle size, temperature and concentration. In the case of particles of known particle size, the change in the central resonance magnetic field, i.e., the g-factor, of the electron paramagnetic resonance spectrum is only temperature dependent and not significantly related to concentration. By utilizing the characteristic, the temperature of organs, tissues and even the inside of cells of a living body can be rapidly and accurately detected, the application scene of magnetic nanometer temperature measurement is greatly widened, and the temperature measurement precision is effectively improved compared with the magnetic resonance temperature measurement.
Description
Technical Field
The invention belongs to the technical field of nano material testing, and particularly relates to a magnetic nanoparticle temperature measuring method based on electron paramagnetic resonance.
Background
Temperature is an important indicator of vital activity. In the field of life sciences, imaging of the temperature distribution of living cells is a significant challenge for scientists. Sensing "thermal events" at the cellular level helps to master the energy changes in the cellular metabolic process, which is of great significance for drug targeting and tumor hyperthermia. However, due to the "sealing" of living bodies, how to non-invasively and accurately perceptually measure these "thermal events" becomes a leading topic and key challenge in life medicine.
In recent years, magnetic thermometry is considered one of the most promising approaches in the field of in vivo thermography due to its good penetration. Magnetic Nanoparticles (MNPs), such as iron oxide nanoparticles, have great potential for development due to their excellent magneto-temperature properties. In 2009, Weaver et al used the ratio of the magnitude of the fifth and third harmonics of the ac magnetization of magnetic nanoparticles to make the temperature measurement error reach 0.3K. From 2011, a teaching team in Liu text systematically studies the mechanism of magnetic nanoparticle temperature measurement, including the excitation mode of a magnetic field and the construction of a temperature measurement model, so that the temperature measurement under multiple scenes is finally realized, and the highest temperature measurement precision reaches 0.1K. This has demonstrated that very high temperature measurement accuracy can be achieved using magnetic nanoparticles as temperature probes. However, one of the major challenges of in vivo thermometry using the above thermometry technique is how to design a large-scale measurement system, and the accurate positioning of particles in vivo is also a problem to be solved.
There are many methods for the localization of iron oxide nanoparticles. In 2005, Gleich, b. et al used a dc gradient magnetic field to perform spatial encoding, and successfully achieved magnetic nanoparticle concentration imaging by detecting the magnetization-related signal of iron oxide nanoparticles at the zero magnetic field point. The fluorescent label can solve the positioning problem of the nano particles in cells or tissues, and indirectly quantify the content of the iron. Spectrophotometry and inductively coupled plasma mass spectrometry are also techniques for assessing the content of iron oxide nanoparticles in vivo. However, the above methods are difficult to expand to the temperature measurement field.
Magnetic resonance technology is a medical imaging technology that is currently in widespread use. Magnetic resonance thermometry uses temperature-dependent proton resonance frequency, relaxation time, and water proton diffusion coefficient to measure temperature. However, the magnetic resonance parameters of water protons are susceptible to tissue structure, motion artifacts, and magnetic field inhomogeneity, thereby reducing the temperature measurement accuracy. The use of contrast agents can improve the accuracy of the temperature measurement. Contrast agents can shorten relaxation times, alter signal intensity, and increase contrast. However, the temperature measurement in vivo can be realized due to the intensity of proton resonance signal, and the temperature measurement precision can only reach 1 ℃.
The signal intensity of electron paramagnetic resonance is far greater than that of nuclear magnetic resonance, endogenous iron in a living body can be distinguished from exogenous iron oxide nanoparticles, and the sensitivity of detecting the concentration of the iron oxide nanoparticles is greatly improved. Therefore, how to utilize the excellent magnetic temperature characteristics of the magnetic nanoparticles to realize high-precision electron paramagnetic resonance temperature measurement has a great promoting effect on the realization of body temperature imaging.
Disclosure of Invention
Aiming at the defects or the improvement requirements of the prior art, the invention provides a magnetic nanoparticle temperature measurement method based on electron paramagnetic resonance, and aims to realize high-precision electron paramagnetic resonance temperature measurement by utilizing the magnetic temperature characteristics of magnetic nanoparticles.
In order to achieve the above object, the present invention provides a magnetic nanoparticle temperature measurement method based on electron paramagnetic resonance, comprising:
s1, selecting and preparing a magnetic nanoparticle sample required by temperature measurement;
s2, adjusting the temperature of the magnetic nanoparticle sample for multiple times, measuring a central resonance magnetic field of an electron paramagnetic resonance spectrum at the corresponding temperature, and calculating a g factor according to the central resonance magnetic field;
s3, constructing a temperature measurement model according to the multiple groups of temperatures and the corresponding g factors; the temperature measurement model represents the relation between the g factor and the temperature T;
s4, for the magnetic nanoparticle sample led into the position to be measured, measuring a central resonance magnetic field of an electron paramagnetic resonance spectrum at the current temperature, calculating a g factor according to the central resonance magnetic field, and calculating according to the constructed temperature measurement model to obtain temperature information.
Further, the particle size range of the magnetic nanoparticle sample required for temperature measurement is 5-25 nm.
Further, the concentration of the magnetic nanoparticle sample ranges from 0.005mg/mL to 5 mg/mL.
Further, the temperature of the magnetic nanoparticle sample is adjusted to be in the range of 10 to 50 ℃ in step S2.
Further, in step S3, the expression of the temperature measurement model is:
wherein a, b and c are constants.
Further, the g-factor is calculated from the central resonance magnetic field, specifically, the central resonance magnetic field B is known, using the formula in steps S2 and S4
Calculating a g factor; wherein v is the microwave frequency.
Further, the introduction amount of the magnetic nanoparticle sample introduced into the position to be detected is matched with the sample cavity of the adopted electron paramagnetic resonance equipment.
Further, the microwave power of the electron paramagnetic resonance device is selected in a linear working area where the magnetic nanoparticles are not saturated.
In general, the above technical solutions contemplated by the present invention can achieve the following advantageous effects compared to the prior art.
The invention utilizes electron paramagnetic resonance equipment to measure the temperature by measuring the change of g factor of the resonance spectrum of the magnetic nanoparticles; specifically, magnetic nanoparticles have superparamagnetism, and the electron paramagnetic resonance spectrum shape of the magnetic nanoparticles is related to particle size, temperature and concentration. In the case of particles of known particle size, the change in the central resonance magnetic field, i.e., the g-factor, of the electron paramagnetic resonance spectrum is only temperature dependent and not significantly related to concentration. By utilizing the characteristic, the temperature of organs, tissues and even the inside of cells of a living body can be rapidly and accurately detected, the application scene of magnetic nanometer temperature measurement is greatly widened, and the temperature measurement precision is effectively improved compared with the magnetic resonance temperature measurement.
Drawings
FIG. 1 is a flow chart of the method of the present invention;
FIG. 2 is an electron paramagnetic resonance simulation spectrogram of magnetic nanoparticles having a particle size of 10 nm;
FIG. 3 is electron paramagnetic resonance spectra at room temperature of magnetic nanoparticle samples of different concentrations;
FIG. 4 is an electron paramagnetic resonance spectrum of a 0.05mg/mL magnetic nanopample at 10 deg.C, 20 deg.C, 30 deg.C, 40 deg.C and 50 deg.C, respectively;
FIG. 5 is a graph showing the variation of resonant magnetic field with temperature;
FIG. 6 is a graph showing the relationship between the change of the g-factor with temperature and a fitting curve thereof;
fig. 7 is a temperature error graph obtained by inversion of experimental data.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
As shown in fig. 1, the present invention provides a magnetic nanoparticle temperature measurement method based on electron paramagnetic resonance, which comprises the following steps:
s1, preparing a magnetic nanoparticle sample required by temperature measurement;
when the grain diameters of the magnetic nano-particles are different, the temperature sensitivity of the g factors of the magnetic nano-particles is also different. The magnetic nanoparticles with the particle size of less than 5nm present superparamagnetism, the g factor of the magnetic nanoparticles is near 2, and the change with temperature is not large; when the particle size is larger than 25nm, the magnetic nanoparticles can have a multi-domain structure, the change of the g factor can become complex, and the magnetic nanoparticles with the particle size of 10nm are selected as the test sample in the embodiment of the invention. Then, for the selected samples, the concentration formulation is also very interesting: too low a concentration can result in too poor signal-to-noise ratio of the signal, which affects the measurement; too high a concentration can result in signal saturation; the concentration range of the invention is optionally 0.005mg/mL to 5mg/mL, and the examples of the invention formulate a range of 10nm samples at concentrations within this range, with the concentration of the sample selected by the test being 0.05 mg/mL.
In order to construct a temperature measurement model, the embodiment of the invention sucks a prepared sample into a capillary tube by utilizing the capillary action; in the X wave band, the dielectric constant of water is larger, and the interaction between the electric dipole of the water and the microwave electric field can cause strong non-magnetic resonance absorption and increase the dielectric loss, so the embodiment of the invention uses a quartz capillary sample tube, the inner diameter is 1mm, the amount of the sample sucked into the capillary is not excessive, the sample is 1.5cm high, the excessive sample can interfere the test, and then the sample is sealed by plasticine.
S2, setting appropriate parameters, adjusting the temperature of the magnetic nanoparticle sample for multiple times, and measuring a central resonance magnetic field of an electron paramagnetic resonance spectrum at the corresponding temperature;
the strength of the electron paramagnetic resonance signal strongly depends on the microwave power on the sample, and the microwave power is selected in an unsaturated linear working region to avoid saturation distortion due to the strong signal of the magnetic nanoparticles; meanwhile, the signal intensity of electron paramagnetic resonance of the magnetic nanoparticles is far stronger than that of an organic free radical signal, the signal is saturated when the microwave power is too high, and the signal-to-noise ratio of the signal is lower when the microwave power is too low, so that the microwave power is set as high as possible under the condition that the signal is not saturated.
The intensity of the signal can be changed greatly along with the change of the temperature or the concentration of the sample, so that the sample with the maximum temperature and concentration is selected to adjust the microwave power for the convenience of subsequent signal processing and comparison, and the microwave power is kept unchanged in subsequent experiments.
In the embodiment of the invention, the electron paramagnetic resonance spectrum of the magnetic nanoparticle sample is measured within the temperature range of 10-50 ℃ at intervals of 10 ℃.
S3, constructing a temperature measurement model according to the multiple groups of temperatures and the corresponding central resonance magnetic fields; the temperature measurement model represents the relation between the g factor and the temperature T;
the formula for calculating the g factor is:
where h is the Planck constant, v is the microwave frequency, βeThe magnetic resonance is a Bohr magneton, B is a resonance magnetic field, so that under the condition of a certain microwave frequency, the resonance magnetic field and the g factor are in a one-to-one correspondence relationship, namely:
the temperature measurement model is constructed, namely the relation between the g factor and the temperature T is as follows:
a. b and c are undetermined coefficients, and the optimal solution of the undetermined coefficients is obtained by using a parameter estimation optimization algorithm.
S4, for the magnetic nanoparticle sample led into the position to be measured, measuring a central resonance magnetic field of an electron paramagnetic resonance spectrum at the current temperature, calculating a g factor according to the central resonance magnetic field, and calculating according to a constructed temperature measurement model to obtain temperature information
According to the temperature measurement model, the following steps are carried out: the current temperature can be easily solved as long as the g-factor of the magnetic nano-sample is known.
Simulation example:
1. simulation model and test description:
in order to investigate the feasibility of the electron paramagnetic resonance-based magnetic nanoparticle temperature measurement method, this example simulated the electron paramagnetic resonance signal of the magnetic nanoparticles. The simulation parameters are as follows: the particle size D is 10nm, the spin quantum number S is 5/2, the nuclear spin quantum number I is 1/2, the scanning range of the main magnetic field is 145-445mT, the microwave frequency v is 9.141GHz, and the simulation temperature is 10 ℃.
2. Simulation test results:
FIG. 2 reflects the electron paramagnetic resonance spectrum of magnetic nanoparticles with a particle size of 10 nm. The graph shows that the spectrum has only one large envelope peak and the g-factor is 2.2316.
Experimental examples:
1. experimental procedures and experimental instructions:
in order to verify the feasibility of temperature measurement of magnetic nanoparticles based on electron paramagnetic resonance, the magnetic nanoparticles with the particle size of 10nm and the concentrations of: 0.005mg/mL, 0.05mg/mL, 0.5mg/mL, 1mg/mL, 5mg/mL of the magnetic nanopattern. The electron paramagnetic resonance device used in the experiment was JES-FA200, manufactured by electronics of Japan. In the experiment, the microwave frequency is 9.141GHz, the microwave power is 3mW, and the magnetic field scanning range is 145-445 mT. The spectral signals of the samples at each concentration were measured separately at room temperature.
The test results of samples with different concentrations were observed and the temperature experiment was performed with the appropriate concentration (here, 0.05 mg/mL). The temperatures in the sample chamber were adjusted to 10 ℃, 20 ℃, 30 ℃, 40 ℃ and 50 ℃, respectively, and the electron paramagnetic resonance spectrum was measured at each temperature. Curve fitting is performed based on g-factor versus temperature, where Levenberg-Marquardt is used for parameter estimation.
2. The temperature measurement experiment results are as follows:
FIG. 3 is electron paramagnetic resonance spectra at room temperature of magnetic nanopatterns at different concentrations; FIG. 4 is electron paramagnetic resonance spectra of magnetic nanopatterns at different temperatures at a concentration of 0.05 mg/mL; FIG. 5 is a graph of the variation of resonant magnetic field with temperature; FIG. 6 is a graph showing the relationship between the change of the g-factor with temperature and a fitting curve thereof; fig. 7 is a temperature error curve. From the experimental results, it can be seen that the temperature error can reach 0.7K when measured by using the method.
Therefore, the magnetic nanoparticle temperature measurement method based on electron paramagnetic resonance can realize non-contact measurement of temperature on the basis of paramagnetic resonance, and widens the application range of magnetic nanoparticle temperature measurement.
It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (8)
1. A magnetic nanoparticle temperature measurement method based on electron paramagnetic resonance is characterized by comprising the following steps:
s1, selecting and preparing a magnetic nanoparticle sample required by temperature measurement;
s2, adjusting the temperature of the magnetic nanoparticle sample for multiple times, measuring a central resonance magnetic field of an electron paramagnetic resonance spectrum at the corresponding temperature, and calculating a g factor according to the central resonance magnetic field;
s3, constructing a temperature measurement model according to the multiple groups of temperatures and the corresponding g factors; the temperature measurement model represents the relation between the g factor and the temperature T;
s4, for the magnetic nanoparticle sample led into the position to be measured, measuring a central resonance magnetic field of an electron paramagnetic resonance spectrum at the current temperature, calculating a g factor according to the central resonance magnetic field, and calculating according to the constructed temperature measurement model to obtain temperature information.
2. The method of claim 1, wherein the sample size of the magnetic nanoparticles required for temperature measurement is in the range of 5-25 nm.
3. The method of claim 2, wherein the concentration of the magnetic nanoparticle sample is in the range of 0.005mg/mL to 5 mg/mL.
4. A method for measuring the temperature of magnetic nanoparticles based on electron paramagnetic resonance according to any one of claims 1 to 3, wherein the temperature of the magnetic nanoparticle sample is adjusted in the range of 10 to 50 ℃ in step S2.
5. The method of claim 1, wherein the expression of the temperature measurement model in step S3 is as follows:
wherein a, b and c are constants.
6. The method as claimed in claim 1, wherein the g-factor is calculated from the central resonance magnetic field in steps S2 and S4, specifically, the central resonance magnetic field B is known, and the formula is used
Calculating a g factor; wherein v is the microwave frequency.
7. The method of claim 6, wherein the amount of the sample introduced into the magnetic nanoparticles at the location to be measured is matched with the sample cavity of the electron paramagnetic resonance device.
8. The method of claim 1, wherein the microwave power of the electron paramagnetic resonance device is selected in a linear operating region where the magnetic nanoparticle absorption spectrum is not saturated.
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