Self-Assembly of Synthetic and Biological Polymeric Systems of ...

DOI: 10.1002/chem.201003679
One-Dimensional Magnetic Nanowires Obtained by Protein Fibril
Biotemplating
JosuØ Juµrez, Adriana Cambón, Antonio Topete, Pablo Taboada,* and
Víctor Mosquera [a]
Abstract: Magnetic nanowires were obtained
through the in situ synthesis of
magnetic material by Fe-controlled
nanoprecipitation in the presence of
two different protein (human serum albumin
(HSA) and lysozyme (Lys)) fibrils
as biotemplating agents. The
structural characteristics of the biotemplates
were transferred to the hybrid
magnetic wires. They exhibited excel-
Introduction
A key issue in nanotechnology is the development of conceptually
simple construction techniques for the mass fabrication
of identical nanoscale structures. Interest in one-dimensional
(1D) nanoscale materials and devices, often
called nanowires, nanotubes or nanorods, has risen sharply
in recent years. In particular, 1D magnetic nanostructures
exhibit unique magnetic properties due to geometric confinement,
magnetostatic interactions and nanoscale domain
formation, [1] which endow them with potential applicability
in data storage and logic devices, [2a] magneto-transport behaviour,
[2b] micromechanical sensors [2c] and biomedicine. [2d]
As a result of their high aspect ratios, 1D magnetic entities
possess larger dipole moments than individual nanoparticles.
This allows their manipulation with lower field strengths [3]
and provides them with improved imaging contrast capabilities,
which opens up the possibility of their use in new biomedical
applications, specifically in the advent of low-field
MRI. [4] Here we report the formation of 1D magnetic nanowires
and assemblies of magnetic nanoparticles over linear
nanosized biopolymer templates formed by spontaneous fibrillation,
under suitable conditions, of two proteins—
human serum albumin (HSA) and lysozyme (Lys)—by in
situ co-precipitation of iron under suitable conditions. These
[a] J. Juµrez, A. Cambón, A. Topete, P. Taboada, V. Mosquera
Grupo de Física de Coloides y Polímeros
Departamento de Física de la Materia Condensada
Facultad de Física, Universidad de Santiago de Compostela
15782 Santiago de Compostela (Spain)
Fax: (+ 34) 881814112
E-mail: pablo.taboada@usc.es
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201003679.
7366
lent magnetic properties as a consequence
of the 1D assembly and fusion
of magnetite nanoparticles as ascertained
by SQUID magnetometry.
Prompted by these findings, we also
Keywords: biotemplating · imaging
agents · magnetic nanowires · nanostructures
· protein fibrils
checked their potential applicability as
MRI contrast agents. The magnetic
wires exhibited large r 2* relaxivities
and sufficient contrast resolution even
in the presence of an extremely small
amount of Fe in the magnetic hybrids,
which would potentially enable their
use as T 2 contrast imaging agents.
magnetic 1D nanostructures possess both high saturation
magnetisations and spin–spin relaxivities at low magnetic
fields, which makes them suitable candidates for use as
imaging contrast agents in MRI.
There are many literature reports on the fabrication of
1D magnetic nanostructures, which can be assembled by (bio)templating,
spontaneous self-assembly by magnetic dipolar
interactions of nanoparticles, chemical synthesis, lithographic
methods, laser etching or microcontact printing. [5]
Owing to its relative simplicity, template-directed synthesis
is one of the most attractive methods for preparing magnetic
1D nanomaterials. [5a,b] This approach offers exciting alternatives
to the costly nanolithography-based “top-down” technologies
or multi-step chemical procedures. Various linear
nanometer-scale materials, including molecular dispersed
and assembled polymers, [6] carbon nanotubes [5a,7] or biological
scaffolds, have been employed to prepare 1D magnetic
structures and assemblies. [8] In particular, the capability of
biopolymers to generate 1D magnetic nanostructures is
really exciting because nature provides a renewable and
highly diverse source of nanometer-scale ordered complexes
that can be used to replicate inorganic materials as well-defined
structures. [9] Dextran, for example, has been used in
the creation of elongated assemblies of spherical nanoparticles
suitable for use as MRI contrast agents and tumour targeting
species. [2d, 10] DNA was also used as a stabiliser for the
formation of ordered nanowires of magnetic nanoparticles.
[2b, 11] These nanowire assemblies resulted in stable magnetic
fluids with high relaxivities at low fields useful for
MRI imaging. The protein cage of cowpea chlorotic mottle
virus (CCMV) was explored with the same goal, to incorporate
high payloads of Gd 3+ with elevated molecular relaxivities,
[12] and the formation either of magnetic nanotubes or of
magnetic nanowires with the aid of magnetic bacteria (Mag-
2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Chem. Eur. J. 2011, 17, 7366 – 7373