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After washing a number of beads remain bound to the surface, which indicates the concentration of the analyte in the sample solution. This is achieved by applying a magnetic field which in turn exerts a force, 0.5 piconewtons, on the magnetic beads. This force is enough to dislodge any non-specifically bound particles but does not break antigen-antibody bonds. Thus the beads that have attached via antigen-antibody bonds exert a force on the cantilever related to the number of antibodies, as illustrated in figure 3. This technique is very sensitive and is dependent on the antibody binding chemistry. |
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Drug Delivery the use of magnetic targeted carriers (MTC) for drug delivery aims to target drugs to a specific site through the application of a magnetic field to achieve prolonged release of high localised concentrations of the drug via the retention of MTC’s in the region of interest. This aims to lower the over all dosage while still achieving effective concentrations at the desired site and limiting the circulation of the drug throughout the body. The system illustrated in figure 4 employs iron particles coated with activated carbon which absorbs the drug providing the drug carrying capacity. The MTC is administered intra-arterially and are targeted via an externally applied magnetic field, which causes them to extravasate through the vascular wall into the targeted tissue. Upon removal of the magnetic field the MTC’s do not recirculate but are retained in the tumour where the drug is desorbed. |
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Figure 4: FeRx Inc. system |
Hyperthermia Treatments the heating of certain organs or tissues to temperatures between 41ºC and 46ºC preferentially for cancer therapy is called hyperthermia. Hyperthermia induces almost reversible damage to cells and tissues; however it enhances radiation injury of tumour cells and chemotherapeutic efficiency. Generally magnetic fluid hyperthermia is achieved by heating biocompatible, coated superparamagnetic particles with an externally applied AC magnetic field thus acting as a localised heat source.
MRI Contrast Enhancement for some applications of MRI the image contrast can be enhances through the use of contrast agents. These are typically paramagnetic or superparamagnetic molecules which distinguish the signal originating from the zone of interest by altering the relaxation times of the tissue.
The final presentation of the afternoon was from Dr. Gareth Hatch of Dexter Magnetic Technologies Inc in which he described the magnetic design considerations for devices used in magnetic biological separation. The two key components in these systems are the magnetic particles used in the separation of the biological entities and the magnetic field used to separate them. However the magnetic field is generated (either by permanent magnets or electromagnets) the aim is the same; generation of a static magnetic field with significant field gradient within the target volume. The field used for separation can be significantly optimised through careful design of key parameters: magnetic material, geometry, configuration and initial magnetisation. These parameters will directly affect the separation time, total yield of target entities, target retention and integrity of the target entities.
