Wright State University Wright State University

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Special Session 5: Carbon and Oxide Based Nanostructured Materials (2012) Special Session 5

6-2012

Magnetic Nanoparticles in Hyperthermia Treatment Magnetic Nanoparticles in Hyperthermia Treatment

Gregory Kozlowski Wright State University - Main Campus, gregory.kozlowski@wright.edu

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MAGNETIC NANOPARTICLES IN HYPERTHERMIA TREATMENT

Gregory Kozlowski Wright State University, Physics Department, 3640 Col. Glenn Hwy., Dayton, OH 45435, USA

Magnetic hyperthermia represents a new non-surgical treatment of

cancerous tumors. In this treatment, some cancerous cells subjected to

elevated temperatures could be selectively destroyed leaving normal

cells unaffected. To achieve this, magnetic nanoparticles introduced to a

malignant tissue have to be subjected to an alternating (ac) magnetic

fields of sufficient intensities (kA/m) and frequencies (kHz - MHz). Due to

the ac magnetic field, the magnetic nanoparticles absorb energy and heat

the surrounding tissue, affecting only the infected cells. In my talk, I will

review the physics of heating mechanisms via magnetic nanoparticles

mostly determined by their sizes and magnetic properties. The

preparation techniques of mono- and bi-metallic magnetic nanoparticles

will be reviewed and their chemical, structural and physical properties will

be discussed in relation to hyperthermia treatment.

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HYPERTHERMIA

Incorporation of Fe2O3 to mammal cell

Magnetic hyperthermia in cancer therapy

Overview

1. Introduction to magnetism

2. Single-domain nanoparticles

3. Magnetic heating (ferrites, Co, Fe, FePt)

4. Conclusions

5. Future work

1. Introduction to magnetism

Origin of Magnetism

Quantum mechanical phenomenon

Orbital motion and spin-1/2 rotational motion

of an electron are the source of magnetism

Dipole

• Maxwell's equations govern magnetism

Magnetic Variables

B, H and M

Magnetization

Magnetization is the measure of the strength of magnetism in a material.

It depends on density of magnetic dipole moments within material (N) and their magnitudes (mS).

ss NM m

Classification of Materials

H

M

Susceptibility (material’s ability to be magnetized due to presence of externally applied magnetic field)

Ferromagnetism : strong and attractive magnetic interaction toward a

magnetic pole.

χ >> 0. Highly dependent on temperature Paramagnetism : interaction is weakly attractive toward a magnetic pole.

χ > 0. Highly dependent on temperature Diamagnetism : interaction is weakly repulsive with respect to a magnetic

pole.

χ < 0. Independent of temperature

Hysteresis Loop (M-H graph)

Shows history nature of magnetization

Applicable for ferromagnetic materials

Magnetization is different with increasing fields as

compared to decreasing fields

M Saturaion

Retertivity

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Saturation

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Magnetic domains exist in order to reduce the

overall energy of the system.

Hysteresis Loop

• Saturation magnetization Ms occurs when all

the domains are perfectly aligned with the

field.

• Remnant magnetization Mr remains when

applied field is removed.

• Coercive field Hc should be applied in

opposite direction to reduce M to zero.

2. Magnetism of single-domain nanoparticles

Size restriction where material cannot

gain favourable energy configuration by

breaking into domains.

Particles smaller than the wall thickness

are single-domain nanoparticles.

Ferromagnetic materials tend to form magnetic domains as domain structure minimizes energy due to stray fields

Schematic of how a material becomes magnetised as the field increases.

Coercivity

• Larger for single-domain nanoparticles

• E.g., Fe (~15nm): 600 - 973 Oe

Fe (>>15nm): 2 Oe

• Process of magnetic reversal:

Domain wall motion

Magnetization rotation by rotation of atomic

spins

Size effect on ferromagnetic/superparamagnetic nanoparticles.

Ferromagnetic nanoparticles undergo a change from multi-domain to single

domain nanoparticles and further reduction in the size modifies their behavior

from ferromagnetic to superparamagnetic. The red curve corresponds to

superparamagnetic state while the blue/green curves are ferromagnetic states.

Superparamagnetism Defined by flips in the overall spin state of the system

due to temperature.

Neel relaxation time (H = 0): kT

KV

oe

• Ordering of the system is not lost, only the orientation of the

ordering (all spins may flip from up to down but retain their

average values)

• Occurs below Tc: Blocking temperature (Tb) by FC-ZFC

• Paramagnetic < χ < Ferromagnetic

Superparamagnetic

3. Magnetic Heating

MAGNETIC NANOPARTICLES

Absorption properties in radio-frequency and microwave range

Nanocrystalline Co2xNi0.5-xZn0.5-xFe2O4 (x = 0, 0.1, 0.2, 0.5) thin films (ferrites) have

been synthesized with various grain sizes by a sol–gel method on polycrystalline

silicon substrates. The morphology, magnetic and microwave absorption properties of

the films calcined in 1073 K were studied with XRD, SEM and vibrating sample

magnetometer. All films were uniform without microcracks. The Co content in Co-Ni-Zn

films resulted in the grain size ranging from 33.5 to 48.7 nm.

The saturation and remnant magnetization increased with increasing the grain size,

while the coercivity demonstrated a drop due to multi-domain behavior of crystallites

for a given value of x. The complex permittivity of the Co-Ni-Zn ferrite films was

measured in the frequency range of 2–15 GHz. The maximum absorption band shifted

from 13 to 11 GHz as the cobalt content was increased from x = 0.1 to 0.2.

RF HEATING SYSTEM

Fiber Optics T. Probe

Coil

Current

Frequency generator

Water Cooling

Vacuum

Supply

HEATING PROCESSES

i. Hysteretic losses

ii. Neel and Brown relaxation M

losses

iii. Frictional losses in viscous

suspensions

Power loss Ferromagnetic

Pf = - f

Superparamagnetic(at lower frequencies)

Ps = m0p0H02f2N/B

Frictional losses

Pfric = 2pf

Specific Power Loss

Since nanoparticles are going to be irradiated by a magnetic field, they are

going to liberate heat to their surroundings.

The term specific power loss (SPL), or more commonly known as

specific absorption rate (SAR) in the medical field, represents the standard

measure of the heating performance of magnetic nanoparticles and is the

power per unit weight of nanoparticles.

DQ = mc DT and P = DQ/Dt

SPL = c (DT/Dt) = P/m

Specific power loss

• Choice of frequency: 100kHz - 400kHz

• Determination of SPL (W/g) or SPL1 (W/g2)

1. Hysteretic loop

2. Calorimetric method

i. Dry powder

ii. Suspension in gel

The diameter of the coil is 3

cm and the length is 4 cm. (a) The magnetic field relative to the position

inside the coil, (b) the legend for the intensity of the field. (a)

Our custom coil consists of insulated

copper sheets wrapped around each other

20 times in the form of a spiral.

(b)

Ambrell EASYHEAT induction heater - The power supply with a coil

mounted on the work head in a zoomed image of the LCD panel and

touchpad. It displays the current flowing through the coil and the frequency

of oscillation.

Inner Diameter: 27 mm Tube Diameter: 6.35 mm

Length: 80 mm

Spacing between the tubes: 6 mm

The magnetic field relative to the position inside the coil with the corresponding legend.

Ni0.5Zn0.5Fe2O4

Ni0.5Zn0.5Fe2O4

RESULTS OF RF HEATING MEASUREMENTS

0

10

20

30

40

50

60

70

SP

L(W

/g)

0 100 200 300 400 500 600 700

Hc (Oe) at 75.6A

Co NANOPARTICLES with several COATING OPTIONS to avoid oxidation

Nanoparticle Diameter

[nm]

Coating

thickness

[nm]

Coating

Co31 6.5 ~0.3 - 0.6

bis(2-

ethylhexyl)

sulfosuccinate

Co51 7.3 ~1 Oleic acid+

Dibutylamine

Co41 8.2 <2

Oleic acid+

Triphenyl

phosphine

Co1 8.7 ~1 Oleic acid

Co21 20.0 ~1.6 PVP

CRITICAL DIAMETER for SINGLE DOMAIN = 15 nm

CRITICAL DIAMETER for SUPERPARAMAGNETISM = 6 nm

Specific Power Loss for Co NANOPARTICLES

Nanoparticle Diameter

[nm]

Coercivity

[Oe]

SPL1(15 A, 348 kHz)

[W/g2] Type

Co31 6.5 0 0.351 Superparamagnet

Co51 7.3 0 0.378 Superparamagnet

Co41 8.2 0 1.316 Superparamagnet

Co1 8.7 ~0 0.176 Single-domain

Ferromagnet

Co21 20.0 601 0.147 Multi-domain

Ferromagnet

CRITICAL DIAMETER for SINGLE DOMAIN = 15 nm

CRITICAL DIAMETER for SUPERPARAMAGNETISM = 6 nm

4. Conclusions

A. Ferromagnetic (ferrites) nanoparticles with

• High saturation magnetization

• Very low coercivity

have the highest specific power loss (SPL).

B. Maximum heating in superparamagnetic

regime is observed for Co nanoparticles

with diameter of 8.2 nm.

5. Future work RF heating characteristics and magnetic properties of

solid colloidal FePt nanoparticles

Typical RF heating curve at 15 A and 200 kHz - temperature

of superparamagnetic nanoparticle (BKFePt3) versus time

Sample Mean diameter (nm)

BKFePt2 8.781

BKFePt3 5.540

BKFePt5 4.407

BKFePt6 2.785

BKFePt7 7.352

BKFePt8 8.295

BKFePt9 3.838

COLLABORATORS

Cambridge University – P. Abdulkin, B. Knappett and A. Wheatley

Queens University, Belfast – T. Houlding and V. Degirmenci

Wright State University, Dayton – A. Sheets, Z. Jagoo and A. Lukawska

AFRL – Z. Turgut, H. Kosai and T. Bixel

FUNDING AGENCIES

AFOSR, EOARD, BRITISH COUNCIL, DAGSI, AFRL, NSF

Thank you