Biomedical Engineering Reference
In-Depth Information
technique has been used mainly to study hard disk write heads. By using super-
sharp tips, Koblishcka
et al
. [83], have shown that HF-MFM enables a higher reso-
lution (20 nm) than standard MFM. As with conventional MFM, the selection of
probe parameters such as thickness and the type of magnetic coating for HF- MFM
requires special consideration [84, 85].
Other upcoming MFM techniques include magnetic exchange force microscopy,
which has been proposed to achieve atomic resolution by revealing the arrange-
ment of both surface atoms and their spins simultaneously, using an external
magnetic fi eld to align the magnetic polarization at the tip apex [86]. In recent
advances, individual atoms have been chemically identifi ed using AFM [87].
Another novel method proposes the combination of three- dimensional electron
spin resonance imaging by magnetic resonance force microscopy (MRFM) and
topographic imaging of the sample surface by surface force magnetometry [88].
Eddy current microscopy may also be developed to serve as another alternative for
the high- resolution imaging of MNPs [89] .
15.13
Summary and Future Perspectives
The scope for MFM lies in detecting the presence of magnetic particles and/or
spatially localizing magnetic dipoles in naturally occurring superparamagnetic or
ferromagnetic particles, especially when these are of nanoscale dimensions. In
biological samples, it is likely that such magnetic nanoparticles occur in clusters
or aggregates, are embedded in a biological matrix to different depths, and are
surrounded by biomolecules of heterogeneous composition. The localization of
such embedded nanoparticles would also involve a careful understanding of the
“shielding” effect of the biological matrices. Even greater challenges lie in develop-
ing MFM for the detection of magnetic particles in fl uids, as the damping forces
on the cantilever are several-fold greater in a fl uid environment. Nevertheless, the
development and application of MFM for detecting superparamagnetic nanopar-
ticles holds great promise in biology for several applications, including the study
of biomagnetism, the use of MNPs for labeling cells and tissues, and for the detec-
tion of endogenous magnetic deposits in tissues. An ability to spatially localize
magnetic plaques at nanometer resolution under ambient atmospheric conditions
will provide a better understanding of the mechanism of nanoparticle and iron
uptake by cells and tissues.
References
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Schreiber , S. , Savla , M. , Pelekhov , D.V. ,
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microscopy of superparamagnetic
nanoparticles .
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( 2 ), 270 - 8 .
3
Martin , Y. and Wickramasinghe , H.K.
( 1987 ) Magnetic imaging by “ force
