CN114112097A - Magnetic nanoparticle temperature measurement method based on electron paramagnetic resonance integral spectrum full width at half maximum - Google Patents
Magnetic nanoparticle temperature measurement method based on electron paramagnetic resonance integral spectrum full width at half maximum Download PDFInfo
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Abstract
The invention belongs to the technical field of nano material testing, and particularly relates to a magnetic nanoparticle temperature measurement method based on the full width at half maximum of an electronic paramagnetic resonance integral spectrum. The magnetic nano-particles have superparamagnetism, and resonance spectrums can be easily obtained by using electron paramagnetic resonance equipment. Research shows that under the condition of certain particle size distribution, the variation of the full width at half maximum of a spectrum after integration is only related to temperature, the concentration variation cannot influence the variation, and the integration operation can partially reduce the influence caused by system noise, so that the temperature measurement is more accurate, and the method can be well suitable for life medicine to carry out in-vivo non-invasive temperature measurement.
Description
Technical Field
The invention belongs to the technical field of nano material testing, and particularly relates to a magnetic nanoparticle temperature measurement method based on electron paramagnetic resonance integral spectrum full width at half maximum.
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 temperature measurement methods have been considered as one of the most promising approaches in the field of temperature imaging due to their good penetration. Magnetic Nanoparticles (MNPs), such as iron oxide nanoparticles, have great potential for development due to their excellent magneto-temperature properties. From 2009, mechanisms of magnetic nanoparticle temperature measurement are systematically researched by a Weaver team, a professor team in Liu text and the like, wherein the mechanisms comprise an excitation mode of a magnetic field, construction of a temperature measurement model, influence of particle size distribution and the like, temperature measurement under multiple scenes is finally realized, and the highest temperature measurement precision reaches 0.017K. However, in vivo temperature measurement using MNP thermometry presents a significant challenge: design of a large magnetic nanoparticle spectrometer (MPS) system. Of course, temperature measurement using magnetic particles as a magnetic resonance contrast agent is a relatively novel way of temperature measurement at present. Hankiewicz et al used doped ferrites as temperature sensors to achieve optimal 0.6K thermometry accuracy on 3T MRI, but the particles are in the micrometer range, whereas in most medical applications the MRI contrast agent needs to be in the nanometer range. Zhang et al performed experiments on a 0.47T NMR apparatus using 5nm iron oxide nanoparticles, and the temperature measurement accuracy reached 0.05K, but the temperature measurement accuracy was significantly reduced at high field.
However, the temperature-sensitive parameters of the two temperature measurement methods are not only related to the temperature, but also affected by the particle concentration, so that the temperature measurement model becomes complicated, and the temperature measurement accuracy is also affected. And temperature imaging for the interior of the living body not only requires accurate measurement of temperature, but also requires accurate positioning of a temperature probe, i.e., iron oxide nanoparticles. There are many methods for measuring the concentration of ferric oxide, in which endogenous iron in vivo can be distinguished from exogenous ferric oxide nanoparticles by electron paramagnetic resonance, which greatly improves the sensitivity of ferric oxide nanoparticle concentration detection. Electron paramagnetic resonance spectroscopy is now widely used for molecular diagnostics, since it shows different spectral lines for different chemical forms of iron.
The excellent magnetic-temperature properties of magnetic nanoparticles provide a possible solution for visualizing temperature imaging inside living bodies, since the human body is "magnetically transparent", but high resolution temperature imaging still faces this great challenge. Therefore, how to combine the temperature measurement principle of the magnetic nanoparticles with an electron paramagnetic resonance spectrometer seeks a high-resolution temperature measurement method, which has a great promotion effect on the realization of body temperature imaging.
Disclosure of Invention
Aiming at the defects and improvement requirements of the prior art, the invention provides a magnetic nanoparticle temperature measurement method based on electron paramagnetic resonance integral spectrum full width at half maximum, and aims to realize high-precision temperature measurement of magnetic nanoparticles.
In order to achieve the above object, according to an aspect of the present invention, there is provided a magnetic nanoparticle temperature measurement method based on electron paramagnetic resonance integral spectrum full width at half maximum, including:
measuring a paramagnetic resonance spectrum of a magnetic nanoparticle sample to be measured at the current temperature, integrating the paramagnetic resonance spectrum to obtain an integral spectrum, and extracting half-height width information in the integral spectrum; calculating to obtain temperature information according to the constructed temperature measurement model based on the half-height-width information;
the temperature measurement model is obtained by adopting the following construction mode:
s1, preparing a magnetic nanoparticle sample required for temperature measurement, sucking the sample into a capillary tube, and placing the capillary tube loaded with the sample into an electron paramagnetic resonance resonant cavity;
s2, setting parameters, and measuring the paramagnetic resonance spectrum of the sample at the current temperature in the cavity;
s3, adjusting the temperature in the cavity for many times, and measuring the corresponding paramagnetic resonance spectrum;
s4, integrating each paramagnetic resonance spectrum, and extracting half-height width information at corresponding temperature;
s5, constructing a temperature measurement model according to the full width at half maximum and the temperature information, wherein the temperature measurement model represents the relation between the full width at half maximum and the temperature.
Further, the inner diameter of the capillary was 1mm, and the height of the sample sucked into the capillary was 1.5 cm.
Furthermore, the particle size distribution of the magnetic nanoparticles in the sample is uniform, and the value range is 5-25 nm.
Further, the concentration of the magnetic nanoparticle sample is 1mg/mL-5 mg/mL.
Further, the microwave power of the electron paramagnetic resonance device is selected in a linear working region where the absorption spectrum of the magnetic nanoparticles is not saturated.
Further, the temperature in the S3 is adjusted within the range of 10-50 ℃.
Further, the temperature measurement model is as follows:
wherein a, b and c are undetermined constants, T*As a temperature, FWHM is full width at half maximum.
Generally, by the above technical solution conceived by the present invention, the following beneficial effects can be obtained:
(1) the invention provides a magnetic nanoparticle temperature measurement method based on the full width at half maximum of an electron paramagnetic resonance integral spectrum, which effectively realizes high-precision temperature measurement of magnetic nanoparticles by obtaining the full width at half maximum of the paramagnetic resonance integral spectrum of a magnetic nanoparticle sample.
(2) According to the magnetic nanoparticle temperature measurement method based on the full width at half maximum of the electron paramagnetic resonance integral spectrum, electron paramagnetic resonance can effectively detect the concentration of magnetic nanoparticles in organs, tissues and even cells of a living body, the magnetic nanoparticles have excellent magnetic-temperature characteristics, an intermediate variable is searched to combine the magnetic nanoparticles and the tissues, and high-resolution detection at body temperature is finally realized.
(3) The invention realizes the temperature measurement of the magnetic nanoparticles by utilizing the corresponding relation between the full width at half maximum of the electron paramagnetic resonance integral spectrum and the temperature, widens the application scene and effectively improves the temperature measurement resolution of the magnetic nanoparticles in the living body.
Drawings
Fig. 1 is a flow chart of a magnetic nanoparticle temperature measurement method based on the full width at half maximum of an electron paramagnetic resonance integral spectrum according to an embodiment of the present invention;
FIG. 2 is an Electron Paramagnetic Resonance (EPR) simulated spectrum and an integral spectrum of magnetic nanoparticles having a particle size of 15nm according to an embodiment of the present invention;
FIG. 3 is electron paramagnetic resonance integral spectra of magnetic nanoparticle samples of different concentrations at room temperature, provided by an embodiment of the present invention;
FIG. 4 is an electron paramagnetic resonance spectrum of a 1mg/mL magnetic nano-sample at 20 deg.C, 25 deg.C, 30 deg.C, 35 deg.C and 40 deg.C, respectively, according to an embodiment of the present invention;
FIG. 5 is an electron paramagnetic resonance integral spectrum of a 1mg/mL magnetic nano sample at 20 deg.C, 25 deg.C, 30 deg.C, 35 deg.C and 40 deg.C, respectively, according to an embodiment of the present invention;
FIG. 6 is a graph showing the relationship between the full width at half maximum of the integral spectrum and the variation with temperature and the fitting curve thereof according to the embodiment of the present invention;
fig. 7 is a temperature error graph obtained by inversion of experimental data according to an embodiment of the present invention.
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 invention provides a magnetic nanoparticle temperature measurement method based on electron paramagnetic resonance integral spectrum full width at half maximum, comprising the following steps:
s1, selecting and preparing a magnetic nanoparticle sample required by temperature measurement;
when the particle size, the preparation method and the like of the magnetic nanoparticles are different, the half-height and width temperature sensitivity of the magnetic nanoparticles are also different. The magnetic nanoparticles with the particle size of less than 5nm present superparamagnetism, the spectral line is narrow, and the half-height width does not change greatly with the temperature; when the particle size is more than 25nm, the magnetic nanoparticles can have a multi-domain structure, the spectrum is greatly broadened, and the extraction of the half-height width is not facilitated; different preparation methods also have great influence on the particle size distribution, and the non-uniform particle size distribution can cause the non-linear broadening of spectral lines, so that magnetic nanoparticles with proper particle size and uniform distribution are selected as test samples, and the method uses the SHP-15 sample prepared by ocean technology. Then a series of concentrations are prepared within the range of 0.005mg/mL-5mg/mL, and after testing, the concentration of the selected sample is 1mg/mL because the accuracy of temperature measurement can be met already when the concentration is 1mg/mL, and higher concentration is not needed.
As the sample is water-based and the dielectric constant of water in X wave band is larger, the electric dipole of water and a microwave electric field interact to cause strong non-magnetic resonance absorption and increase the dielectric loss, the quartz capillary sample tube with the inner diameter of 1mm is adopted, the sample amount absorbed into the capillary is not excessive, the sample amount is 1.5cm high, the test is interfered when the sample amount is excessive, and then the sample is sealed by plasticine.
S2, setting appropriate parameters and measuring an electron paramagnetic resonance signal at the current temperature;
the intensity of the electron paramagnetic resonance signal is strongly dependent on the microwave power on the sample. Because the signal of the magnetic nano-particles is strong, the microwave power should be selected in the unsaturated linear working area to avoid saturation distortion. And 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.
S3, adjusting the temperature of the magnetic nano sample in the sample cavity, and measuring again;
electron paramagnetic resonance spectra of magnetic nanopatterns were measured at 10 ℃ intervals around physiological temperature, i.e. in the temperature range of 10-50 ℃.
And S4, integrating the electron paramagnetic resonance spectrum, calculating the full width at half maximum, and constructing a temperature measurement model according to the relation between the full width at half maximum and the temperature.
The relation between the constructed full width at half maximum and the temperature T is as follows:
and a, b and c are undetermined coefficients, and the optimal solution of the undetermined coefficients is obtained by using a parameter estimation optimization algorithm.
The following formula shows that: as long as the full width at half maximum of the resonance integral spectrum of the magnetic nano sample is known, the temperature can be easily solved:
s5, for the magnetic nanoparticle sample led into the position to be measured, measuring the full width at half maximum of an electron paramagnetic resonance integral spectrum at the current temperature, and obtaining temperature information according to a temperature measurement model.
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 diameter D is 15nm, the scanning range of the main magnetic field is 76-576mT, the microwave frequency v is 9.141GHz, and the simulation temperature is 30 ℃. Magnification factor
2. Simulation test results:
fig. 2 reflects the electron paramagnetic resonance spectrum and the integral spectrum of magnetic nanoparticles with a particle size of 15 nm. It can be seen from the figure that there is only one resonance peak.
Experimental examples:
1. experimental procedures and experimental instructions:
in order to verify the feasibility of the temperature measurement method of the magnetic nanoparticles based on the full width at half maximum of the electron paramagnetic resonance integral spectrum, the temperature measurement method is characterized in that the particle size is 15nm, and the concentrations are as follows: 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 76-576 mT. The spectral signals of the samples at each concentration were measured separately at room temperature.
The test results of samples with different concentrations are observed and compared, and the temperature experiment is carried out by selecting the appropriate concentration (here, 1mg/mL is selected). The temperatures in the sample cavity were adjusted to 20 ℃, 25 ℃, 30 ℃, 35 ℃ and 40 ℃, respectively, and the electron paramagnetic resonance spectrum was measured at each temperature. Curve fitting was performed based on half-height width versus temperature, where Levenberg-Marquardt was used for parameter estimation.
2. The temperature measurement experiment results are as follows:
FIG. 3 is electron paramagnetic resonance integral spectra of magnetic nano-samples at room temperature at different concentrations; FIG. 4 is electron paramagnetic resonance spectra of magnetic nanopatterns at a concentration of 1mg/mL at different temperatures; FIG. 5 is electron paramagnetic resonance integral spectra of magnetic nano-samples with concentration of 1mg/mL at different temperatures; FIG. 6 is a graph showing the relationship between the variation of full width at half maximum and the variation of full width at half maximum with temperature and a fitting curve thereof; fig. 7 is a temperature inversion error. From the experimental results, it can be seen that the temperature error can reach 0.1K when the method is used for measurement.
Therefore, the magnetic nanoparticle temperature measurement method based on the full width at half maximum of the electron paramagnetic resonance integral spectrum can realize non-contact measurement of the 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 (7)
1. A magnetic nanoparticle temperature measurement method based on electron paramagnetic resonance integral spectrum full width at half maximum is characterized by comprising the following steps:
measuring a paramagnetic resonance spectrum of a magnetic nanoparticle sample to be measured at the current temperature, integrating the paramagnetic resonance spectrum to obtain an integral spectrum, and extracting half-height width information in the integral spectrum; calculating to obtain temperature information according to the constructed temperature measurement model based on the half-height-width information;
the temperature measurement model is obtained by adopting the following construction mode:
s1, preparing a magnetic nanoparticle sample required for temperature measurement, sucking the sample into a capillary tube, and placing the capillary tube loaded with the sample into an electron paramagnetic resonance resonant cavity;
s2, setting parameters, and measuring the paramagnetic resonance spectrum of the sample at the current temperature in the cavity;
s3, adjusting the temperature in the cavity for many times, and measuring the corresponding paramagnetic resonance spectrum;
s4, integrating each paramagnetic resonance spectrum, and extracting half-height width information at corresponding temperature;
s5, constructing a temperature measurement model according to the full width at half maximum and the temperature information, wherein the temperature measurement model represents the relation between the full width at half maximum and the temperature.
2. The method of claim 1, wherein the capillary has an inner diameter of 1mm and the height of the sample drawn into the capillary is 1.5 cm.
3. The method according to claim 1, wherein the magnetic nanoparticles have a uniform particle size distribution and a range of 5-25 nm.
4. The method for measuring the temperature of magnetic nanoparticles according to claim 1, wherein the concentration of the sample of magnetic nanoparticles is 1mg/mL to 5 mg/mL.
5. 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.
6. The method for measuring the temperature of magnetic nanoparticles according to claim 1, wherein the temperature in S3 is adjusted within a range of 10-50 ℃.
7. The method of any one of claims 1 to 6, wherein the temperature measurement model is:
wherein a, b and c are undetermined constants, T*As a temperature, FWHM is full width at half maximum.
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| CN114486979A (en) * | 2022-04-14 | 2022-05-13 | 国仪量子(合肥)技术有限公司 | Method for acquiring absolute spin number of unpaired electrons of sample |
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