Annual Report 2011 / 2012 - E21 - Technische Universität München

14 E21 Annual Report 2011/2012
Biofunctionalized Magnetic FePt Nanoparticles
K. M. Seemann 1, 2 , A. Bauer 1 , J. Kindervater 1 , R. Georgii 1, 2 , P. Böni 1
1 Physik-Department E21, Technische Universität München, D-85748 Garching, Germany.
2 Forschungsneutronenquelle Heinz Maier-Leibnitz (FRM II), Technische Universität München, D-85748 Garching, Germany.
We use polyoxometalates as coating molecules, a choice
motivated by their high thermodynamic stability, their
well-established potential to stabilize metallic (noble metal)
nanoparticles and the fact that this class of compounds and
their derivates have lately been considered for their anticancer
properties (Fig. 1). The magnetic properties of the
SiW 11 -Fe 2 Pt core-shell nanoparticles in comparison to the
non-coated Fe 3 Pt nanoparticles are examined by conventional
low temperature magnetometry. Another advantage of
polyoxometalates is that their solubility in various media can
be tuned by exchange of the associated cations [1]. This
opens up possibilities to adjust the degree of dispersibility of
nanoparticles in aqueous media (Fig. 2).
Figure 1: Schematic of the core-shell Fe 2Pt nanoparticle structure
(a). The inorganic polyoxometalate cluster molecule coats
the iron-platinum core particle by chemisorption. Comparative
infra-red spectra of the core-shell nanoparticles show the characteristic
IR bands of the silico tungstate cluster (b).
A shifted stoichiometric content of Fe within the core
crystallite from iron-rich Fe 3 Pt for the non-coated nanoparticles
to Fe 2 Pt in the core-shell nanoparticles is the main
motivation for magnetometric measurements, as the magnetic
moment is expected to be considerably reduced for
the core-shell nanoparticles containing one third less Fe than
the non-coated ones. The magnetization versus field scans
were recorded for the core-shell nanoparticles as well as for
the non-coated nanoparticles for applied magnetic fields up
to ±9 Tesla and temperatures ranging from 300 K to 2 K.
Figure 3: The core-shell nanoparticles are superparamagnetic in
the as-made state, i.e. no phase change to a hardmagnetic L1 0
-phase has been performed yet. The blocking temperature lies
well below 10 K (inset in the upper right corner). Upon introducing
a mono-vacant polyoxometalate shell the stoichiometry
of the iron-platinum core shows a reduced iron content, consequently
a significantly lower magnetic moment is measured. At
a temperature of T = 2 K the transition to ferromagnetism is
observed.
The samples were measured in their as-made state, i.e.
no annealing procedure at elevated temperatures was carried
out (Fig. 3). The core-shell nanoparticles are superparamagnetic
in the as-synthesized state with a blocking temperature
well below T = 10 K. The bio-functionalization of the
bare Fe 2 Pt nanoparticles that were carboxylated by MUA
and dispersible in de-ionized water (Fig. 4) was exemplified
directly by coupling of the nanoparticles with a bio-organic
compound phenylalanine.
Figure 2: The advantage of using the silico tungstate cluster
molecule as shell materials is the dramatically enhanced water dispersibility
of the core-shell nanoparticles. The nanoparticles are
readily dispersible in the polar organic solvent ethanol (a) and also
water (b). Using mercapto alkanes, the water dispersibility of the
nanoparticles is maintained and offers the possibility for coupling
reactions with biological molecules (c). The as-made core-shell
(d) and bare nanoparticles (e) are clearly non-dispersible in water
due to the organic non-polar ligands necessary for their chemical
synthesis.
Figure 4: Via an amide-coupling reaction after a ligand exchange
using mercapto compounds the core-shell nanoparticles were successfully
biofunctionalized with the amino acid phenylalanin. The
UV-VIS absorption spectra of the biofunctionalized iron-platinum
nanoparticles show the characteristic bands of the amino acid at
a wavelength of 250-270 nanometers.
Diam. core-shell Fe 2 Pt /nm core 2.3±0.3 tot. 4.8 ± 0.5
Diam. bare Fe 3 Pt /nm 3.1±0.2 n.a.
Table 1: Diameter distribution of core-shell iron-platinum nanoparticles
in comparison to the bare nanoparticles.
References
[1] K. M. Seemann , A. Bauer, J. Kindervater, M. Meyer, C. Besson,
M. Luysberg, P. Durkin, W. Pyckhout-Hintzen, N. Budisa, R.
Georgii, C.M. Schneider and P. Kögerler, Nanoscale 5 2511-2519
(2013).