superparamagnetism and its biological applications
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Transcript of superparamagnetism and its biological applications
Few subjects are more difficult to understand than magnetism.
Encyclopedia Britannica
Presented By- R. UDAY KIRAN
Superparamagnetism and its Biological Applications
Nanotechnology Plays by Different Rules
Normal scale Nanoscale
3
Description of magnetic particles
MESOSCOPIC MAGNETISMmacroscale nanoscale
permanentmagnets
micronparticles
nanoparticles clusters molecularclusters
Individualspins
S = 1023 1010 108 106 105 104 103 102 10 1
multi - domain single - domain Single molecule nucleation, propagation andannihilation of domain walls
uniform rotation quantum tunneling,quantum interference
-1
0
1
-40 -20 0 20 40
M/M
S
m0H(mT)
-1
0
1
-100 0 100
M/M
S
m0H(mT)
-1
0
1
-1 0 1
M/M
S
m0H(T)
Fe8
1K0.1K
0.7K
Mn12-ac
Ferritin
1 nm10 nm100 nmsuperparamagnetism
Classical Quantum
size
Natural Nanomagnets:
• Ferritin
Man on average has 3-4 g of iron 30 mg per day are exchanged in plasma. Ferritin stores iron in mineral form; Ferritins are found in animals, vegetables, mushrooms and bacteria
The internal core, 7 nm, may contain up to 4,000 iron(III) ions Approximately FeO(OH) Magnetism depends on the number of ions Magnetic measurements provide information on the number of ions in the core
• Magnetosomes
Nanomagnets embedded in cell membranes
• Magnetotactic bacteria iron core
Magnetism in reduced dimensions
Intrinsic properties
Finite-size effects
Surface effects
Interparticle interactions
Nanomagnetism
Size, aspect ratio distribution
Magnetism in reduced dimensions
Surface effects
• lower coordination number• broken magnetic exchange bonds• frustrated magnetic interactions• surface spin disorder• reduced M in ferri-, antiferro-systems• enhanced M in metallic ferro-systems
Surface and core magnetic orders
spin glass?dead magnetic layer?
bulk-like?
• high-field irreversibilities
• high saturation fields
• shifted hysteresis loops
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Magnetic Moment vs. Cluster Size
Figure above from: Billas et al., J. Magn. Magn. Mater. 168 (1997) 64
Superparamagnetism• Superparamagnetism (SPM) is a type of magnetism that occurs in
small ferromagnetic or ferrimagnetic nanoparticles.• This implies sizes around a few nanometers to a couple of tenth of
nanometers, depending on the material.• Additionally, these nanoparticles are single-domain particles.• In a simple approximation, the total magnetic moment of the
nanoparticle can be regarded as one giant magnetic moment, composed of all the individual magnetic moments of the atoms which form the nanoparticle.
Tk
KV
B
exp0
Superparamagnetism
For a magnetic particle the magnetic energy with uniaxial anisotropy is given by
For particles with nanometric dimensions
Superparamagnetic relaxation is the spontaneous fluctuations of the magnetization direction such that it alternately is near θ=00 and θ=1800. The superparamagnetic relaxation time τ is given by
where τ0 is of the order of 10-10-10-13 s, kB is the Boltzmann’s constant and T is the temperature.
2sinKVE
KVTkB
Superparamagnetism (SPM)
τ=τ0exp(E / (kBT)) Neel-Arrhenius equation
τ – Average length of time that it takes for a ferromagnetic cluster to randomly flip directions as a result of thermal fluctuations
τ0 – Attempt period (characteristic of the material)
E – Anisotropic energy which is proportional to V
E=KV K is the anisotropy energy density constant
Superparamagnetism (SPM)
Blocking temperature Tb E=KV=25kBTb
T>Tb τ < <τ0 Behave like Paramagnetic particle
T<Tb τ > >τ0 Magnetic ordering and open loops
If V↓ then τ ↓ SPM limit of hard drives
REF: IEEE Transaction on Magnetics Vol 33, No. 1(1997)978-983 An upper bound of about 36 Gbit/in.2
τ=τ0exp(E / (kBT)) Neel-Arrhenius equation
• What are the implications of such superparamagnetic states? Without external magnetic field, the net moment is zero. As soon as
an external field is applied, the nanoparticles react similar to a paramagnet (hence the “paramagnetism” in the name) with the one exception that their magnetic susceptibility is much larger (hence the “super” in the name).• A word of clarification: Normally, any ferromagnetic or ferrimagnetic
material can behave paramagnetically. This is from a certain temperature on and upwards, the so called Curie temperature Tc • However, superparamagnetic behaviour is observed below the Cure
temperature and thus has to be explained differently.
New Properties of SPM
• Small size and larger magnetic moment for each particle like Ferromagnetism --Large MS
• Response to external field like paramagnetic response---No open loop
• Superparamagnetic relaxation
τ=τ0exp(E / (kBT)) Neel-Arrhenius equation
Paramagnet, Ferromagnet & Superparamagnet
Zero Magnetic Field
Magnetic Field Applied
Paramagnet Domain moments align randomly—no net moment.
Net moment appears; the applied magnetic field helps the domains “find” each other to become coupled.
Ferromagnet Domain moments coupled (below Curie temp.) to produce strong, permanent moment.
Even higher magnetic moment.
Superparamagnet
Domain moments that would couple as in Ferromagnet do not do so because of small size—boundary effect.
Domains “find” each other and now it generates a moment comparable to Ferromagnet.
Types of Magnetism
Application of Magnetic Nanoparticles in Biomedicine
• Their size is comparable to the targeted entities.• Nanoparticles can be magnetic. An external magnetic field gradient
can be applied to influence their movement. This way, they can either deliver certain drugs or tag certain entities.• Nanoparticles may also be resonantly excited. This allows heat
transfer to the surrounding tissue.
Radionuclide and Gene Delivery• Radionuclide Delivery: An advantage of radionuclide therapy is that
the radionuclides do not have to decouple from the magnetic carriers. The magnetic carriers can transport the radionuclides to the target area where they can destroy the cancerous tissue. After the desired result has been achieved, both the carriers and the radionuclides can be directed out of the circulatory system.• Gene Therapy: In gene therapies, the magnetic carriers are coated
with the therapeutical gene and transported to the target area. Thanks to the possibilitiy of holding the gene and carrier at the target for an extended time, the chances rise that the gene can get transfected. Applications in this field of study are only in their beginning
Ferrofluids: Suppose some particles do have magnetic moments.
N S N S N S N S
They will chain together!
The chain causes high viscosity.
Magnetorheological effect.
Magnetorheological Effect
A magnetic fluid.
Just pretty.
Hyperthermia:• Hyperthermia is usually an unwanted overheating of the body not to
be confused with common fever. In a hyperthermic state, the body absorbes or produces more heat than it can dissipate. However, hyperthermia can also be a wanted effect in order to destroy tumorous cells and hence is sometimes created artificially.• The magnetic particles first have to be brought to the target area,
where they can be caused to heat up by an AC magnetic field of sufficient strength and frequency. The heat should exceed the threshold of 42 degree Celsius and last for about 30 minutes in order to properly destroy the tumour.
Mechanism of heating process for MNPs Hyperthermia
1. Hysteresis loss
Hysteresis loss at different temp.
Applied field H(T)
Mag
netiz
ation
(em
u/g)
Tc
T2T1
2. Neel mechanism Rotation of the magnetization vector within the particles.
3. Brownian Mechanism Mechanical rotation of the magnetic particle
Intrinsic superparamagnetism(the particle magnetic moments aligns with external field)
Extrinsic superparamagnetism(the particle itself aligns with field)
H
H=0 H ≠ 0
H=0
Neel relaxation
H = 0
Brownian relaxation
Magnetic relaxation mechanisms
Drug Delivery The advantages of targeted drug delivery seem numerous: Most drugs are non-specific, i.e. they get distributed over the
whole body as soon as they get administered intravenously. Targeted delivery can ensure that only specific areas get
influenced by the (otherwise harmful) drugs and as little as possible of the drug needs to be administered. This method seems especially applicable, when the drug is very damaging to healthy tissue.
Fields of application:• Chemotherapy,• radionuclide therapy,• arthritis or• gene therapy.
Gene Delivery
Att tillföra en ny gen i en cell
• FeOfection is a solution of nanoparticles with an iron oxide core.
• The core is stable and the magnetic properties can be used e.g. in tracking of cells with MRI.
• The surface of the particles are modified to promote binding of DNA to the particles and facilitate transport of the resulting particle/DNA complexes into cells.
• FeOfection can be used for both transient (temporary expression) and stable (incorporated in the genome) transfection.
Imaging using magnetic nanoparticles
Marknaden drivs av ett medicinskt behov av effektivare och känsligare diagnostik
Iron Oxide
NH
2
Phospholipid
Amino-PEG
NHS-Alexa 647
Iron Oxide
NH2
U-2 OS cell incubated with Alexa-647 magnetic nanoparticles for 1 hour
FeOdots incubated with cells and exposed to a magnetic field
NH 2
NH2
Imaging - Regenerative medicine
Stamceller märks med Genovis magnetiska nanopartiklar ex vivo och injeceras i mus T2* Map Prussian blue
positive cells at edge of tumor
C6 glioma
FeOlabeled cells were injected i.v. in C6 glioma in mouse flank 14 days prior to 3T MRI
Cells labeled with FeOlabel can easily be visualised with MRI.
Mesenchymal stem cells were labeled with FeOlabel and then injected into a mouse with a C6 glioma. After 14 days the cells are visible with MRI. Particles can also be visualised by Prussian Blue iron staining.
Challenges in Nanomagnetism
100% spin-polarizedmaterials
MagneticlogicInstant boot-up
computerSpin-transistor
with gain
RT magneticsemiconductors
Nano-bioMag-sensors
Ultra-strongPermanent
Magnets
UltraHigh density
media
Opportunities in Nanomagnetism
Superparamagnetism
Superparamagnetism paramagnetism below Curie’s temperature large susceptibility superparamagnetism limit
Origin of superparamagnetism magnetism: result of spin alignment thermal excitation, ferromagnetism <-> paramagnetism small scale, below Tc:
thermal excitation destroys the ordering between the clusters thermal excitation cannot upset alignment within the cluster ferro~ inside & para~ outside => treated as a large spin as a whole
Experiment results stepped hysteresis can be found below certain temperature. frequency dependent AC susceptibility
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