Chapter 6: Applications in Medical and BiologyMagnetic nanoparticles... Chapter 6: Applications in Medical and BiologyMagnetic nanoparticles Hard Magnets: HC and Mrs have high values...
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Applications in Medical and Biology
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Trang 4Magnetic nanoparticles
Trang 5Chapter 6: Applications in Medical and Biology
Magnetic nanoparticles
Trang 6Magnetic nanoparticles
Materials: Fe, Co, Ni, Gd
Spins of unfilled d-bands spontaneously align parallel inside a domain below a critical temperature TC (Curie) Laws:
B = H +4H
M = H
: Susceptibility
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Magnetic nanoparticles
Hard Magnets: HC and Mrs have high values
Trang 8Superparamagnetism - a size effect
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Superparamagnetism - a size effect
Superparamagnetism:
• high saturation magnetisation MS
• no remanence MR = 0
Trang 10The Néel relaxation in the absence of magnetic field
Normally, any ferromagnetic or ferrimagnetic material undergoes a transition to a paramagnetic state above its Curie temperature Superparamagnetism is different from this standard transition since it occurs below the Curie temperature of the material
Superparamagnetism occurs in nanoparticles which are single domain This is possible when their diameter is below 3–50 nm, depending on the materials
In this condition, it is considered that the magnetization of the nanoparticles is a single giant magnetic moment, sum of all the individual magnetic moments carried by the atoms of the nanoparticle
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Magnetic anisotropy is a prerequisite for hysteresis in ferromagnets: without it, a ferromagnet is superparamagnetic
Trang 12• E = KVsin2θ (simplest form)
– K the effective uniaxial anisotropy energy per unit volume
– V particle volume
– θ angle between moments and easy axis
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Magnetic anisotropy
Trang 14Because of the nanoparticle’s magnetic anisotropy, the magnetic moment has usually only two stable orientations antiparallel to each other, separated by
an energy barrier
The stable orientations define the nanoparticle’s so called “easy axis”
At finite temperature, there is a finite probability for the magnetization to flip and reverse its direction The mean time between two flips is called the Néel relaxation time τN and is given by the following Néel-Arrhenius equation:
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• K is the nanoparticle’s magnetic anisotropy energy density and V its volume.
• KV is therefore the energy barrier associated with the magnetization moving from its initial easy axis direction, through a “hard plane”, to the other easy axis direction
• kB is the Boltzmann constant andT is the temperature
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Trang 17Chapter 6: Applications in Medical and Biology
Superparamagnetism - a size effect
Trang 18Cell Sep
ara tion
Trang 19Chapter 6: Applications in Medical and Biology
Nanomagnetic Particle
Trang 21Chapter 6: Applications in Medical and Biology
Trang 22Magnetic Cell Separation / Cell Labeling
Trang 23Chapter 6: Applications in Medical and Biology
Magnetic Cell Separation / Cell Labeling
Trang 24Capture of bacteria by using Vancomycin-conjugated magnetic nanoparticle
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Magnetic Drug Delivery
Trang 26However, in nucleus with odd mass #, spin directions are not equal and
opposite, so the nucleus has net spin or angular momentum.
These are know as MR active nuclei.
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MR active nuclei that have a net charge and are spinning (motion), automatically acquire a magnetic moment and can align with external magnetic field
The strength of the total magnetic moment is specific to every nucleus and determines the sensitivity to magnetic resonance
Trang 28MRI - The hydrogen nucleus
The hydrogen nucleus is the MR active nucleus used in clinical MRI It contains a single proton (atomic and mass number 1)
It is used because it is most abundant in the human body and its solitary proton gives it a relatively large magnetic moment
Both of these characteristics enable utilization of the maximum amount
of available magnetization in the body
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The hydrogen nucleus as a magnet
The laws of electromagnetism state that a magnetic field is created when
a charged particle moves
The hydrogen atom contains one positively charged proton that spins
Therefore it has a magnetic field induced around it, and acts as a small magnet
It has a north and south pole
Each of which is represented by a magnetic moment
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The MR signal
When a patient is placed within and MR scanner, the protons in the patients tissues (primarily protons contained in water molecules) align themselves along the direction of the magnetic field
A radiofrequency electromagnetic pulse is then applied, which deflects the protons off their axis along the magnetic field
As the protons realign themselves with the magnetic field, a signal is produced
This signal is detected by an antenna, and with the help of computer analysis, is converted into an image
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MRI of a Female Rat