MNPs utilisation in Biomedical Applications

Chemistry & Characterisation of Thin Films & Surfaces

Asterios Ntais

MNPs - Introduction •  Fe – Co – Ni – Metal oxides •  manipulation by external Magnetic Field

•  size ≈ biological components (drug delivery) •  surface + magnetic moment (in vivo MRI) •  absorbed energy into heat (hyperthermia)

•  colloidal stability | no agglomeration

•  Properties depend on: magnetic anisotropy – composition – vacancies crystal structure – size – shape

atomic magnetic dipole (orbital + spin motion) magnetic order (Tc ≤)

e- arrangements

∨ magnetic behaviour

size ≤ 100nm: 1.  single magnetic

domain 2.  magnetisation

reversal = uniform 3.  function of T

Synthesis of MNPs 1.  Gas-phase methods (s-precipitates from g-phases) •  CVD: volatile precursors – high T (size & growth control) •  Laser pyrolysis: thermochemical decomposition •  ultrapure & high quality products | low yield 2. Wet chemical methods (simple, inexpensive, better yield) •  Coprecipitation: precipitation of aqueous solution + base •  Massart Method: alkaline coprecipitation of ferrous & ferric salt •  pH, [cations], temperature – dependent •  Fe3O4, γ-Fe2O3

•  uniform size distribution | nucleation & growth

i.e. iron oxides from Fe(Co)5

Synthesis of MNPs 3. Thermal decomposition (rapid process) •  unstable precursors into hot-aqueous solution •  organometallic & inorganic precursor, temperature, reaction time •  complexes bound to iron via oxygen •  surfactants (fatty acids) mediate nucleation & growth rates

4. Microemulsion •  H2O nanodroplets in oil stabilised by surfactants

•  A, B reagents dissolved in 2 emulsions •  mixing – AB precipitation, trapped w/in H2O droplets •  size and shape control •  iron oxide NPs

Surface modification •  need for chemical stability & functionalities - biofunctionalisation •  high [protein] & [salt] environments

•  H2Ophilic / H2Ophobic •  ligands & coatings (organic molecules, surfactants, polymers)

Avoid: immune responses | protein synthesis failure clotting | generation of ROS (!!!)

Main goals: 1.  conservation of magnetic properties 2.  increased biocompatibility – decreased toxicity

Biomedical Apps of MNPs •  Magnetic Hyperthermia eliminate cancer cells @ 42 - 45oC (locally) application of an AC magnetic field •  Drug Delivery MNPs: drug or antibody carriers to specific organs / tissues fight w/ forces of blood flow magnetic guidance particle size: 10 – 100nm surface engineering to minimise interactions w/ phagocytic cells

Energy loss HEAT

Biomedical Apps of MNPs •  Magnetic Resonance Imaging MNPs serve as contrast agents need for high chemical stability and magnetisation extensive use of maghemite (γ-Fe2O3) size ≤ 50nm: imaging of gastrointestinal, liver, spleen, lymph nodes size ≥ 50nm: diffusion imaging & brain / myocardial imaging appropriate for enzyme activity imaging (apoptosis, cancer, metastasis, inflammatory responses) functionalisation of MNPs w/ monoclonal antibodies

Characterisaton techniques •  X-Ray Diffraction mapping of a material | chemical identification

•  Transmission Electron µScopy structural characterisation @ atomic scale resolution

•  Fourier Transform Infrared Spectroscopy “fingerprint” of a molecule MNPs: size, shape, element, phase identification

•  Vibrating Sample Magnetometer Faraday’s principle (a changing magnetic field produces an electric field) delivers information about saturation magnetisation, coercivity, shape anisotropy, energy loss

Thanx Questions?