AVS 58th Annual International Symposium and Exhibition
    Nanometer-scale Science and Technology Division Thursday Sessions
       Session NS-ThA

Paper NS-ThA4
Ultrastable Superparamagnetic Nanoparticle Design for Membrane Assembly and Triggered Release

Thursday, November 3, 2011, 3:00 pm, Room 203

Session: Biological Nanomaterials
Presenter: Erik Reimhult, University of Natural Resources and Life Sciences Vienna, Austria
Authors: E. Amstad, ETH Zurich, Switzerland
M. Textor, ETH Zurich, Switzerland
E. Reimhult, University of Natural Resources and Life Sciences Vienna, Austria
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Application of superparamagnetic iron oxide nanoparticles as biomedical imaging contrast agents and as actuators in smart materials, e.g. for drug delivery and release, require them to retain high stability even in extremely dilute suspensions, high salt and at elevated temperatures. These requirements can only be met by steric repulsive stabilization through irreversibly binding, low molecular weight dispersants of e.g. poly(ethylene glycol) or a similarly irreversibly bound organic shell which stabilizes the nanoparticle into another matrix material.

We have recently demonstrated that we can stabilize magnetite nanoparticles which fulfil these stability criteria using self-assembling dispersants with nitrocatechol anchors (1-2). This allows us free control over the dispersant type by simple co-adsorption of dispersants to as-synthesized core Fe3O4 particles. Combined with independent control over the Fe3O4 core size in the range 3-15 nm a versatile toolbox for assembly of various smart materials and for biomedical applications has been created.

This presentation is focussed on recent results demonstrating and characterizing assembly of such nanoparticles into membranes of stealth liposomes (3). We show that there are strict requirements for the size of particles that can be assembled into lipid bilayer membranes and that a requirement for efficient assembly and actuation as well as liposome stability is to ensure stability of the hydrophobic shell surrounding the nanoparticle within the membrane. Encapsulated molecules were released multiple times by application of short bursts of alternating magnetic fields through a localized phase change in the membrane without heating of the surrounding aqueous environment. This allowed control of both timing and dose of release. The highest efficiency of release and encapsulation was obtained for irreversibly stabilized superparamagnetic iron oxide nanoparticles with diameters <6 nm inserted into the lipid membrane.

1. E. Amstad et al., Nano Lett, 9:4042 (2009)

2. E. Amstad et al., J Phys Chem C 115:683-691 (2011)

3. E. Amstad et al., Nano Lett, 11:1664-1670 (2011)