Biomedical Engineering Reference
In-Depth Information
care must be exercised in selecting reporter molecules with a minimal
amount of spectral overlap and similar scattering cross sections. The
latter criterion is particularly important when luorescent molecules
are used as Raman reporter. The Raman cross section of luorophors
can be very different when excited on and off electronic resonance
thus resulting in orders of magnitude difference in the observed
SERS intensity.
11.3
SERS-Based Bioimaging with
Multifunctional Nanoparticles
An important frontier in molecular imaging is the utilization of the
inordinate sensitivity of SERS to achieve target-speciic detection of
cellular proteins
in vivo
. SERS microscopy applied in cellular imaging
has been used to study the localization of HER2 and CD10 on cell
membranes,
62
to examine the over-expression of phospholipid Cγ1
in human embryonic kidney (HEK293) cells,
61
to image the EGFR
expression in human hepatoma (Huh7.5) cells,
66
and to locate the
β-adrenergic receptors in cardiac myocyte (H9C2) cells.
67
It has also
been applied to study the cell surface receptors in mammalian cells
68
as well as for tissue immunohistological assay in cancer pathology.
69
In every regards, SERS labels rival that of luorescent contrasting
agents and can be adapted to most of the luorescent detection
schemes. In this section, we outline SERS imaging of cell surface
receptors in mammalian cells as well as in a localization study of
receptor-driven aggregation.
Figure 11.8 shows a cartoon representation of the generic cell-
labeling method. NPs designed for cellular imaging must meet the
following criteria. They must be water-soluble, highly speciic,
biocompatible, and stable toward substitution. Also, they must not
alter the biochemistry of host cells as nontoxic metals are known
to do. Ideally, the size of the particles should be comparable to the
proteins and receptors they target on cell surfaces — typically less
than 20 nm in diameter. Many of the core-shell type of SERS probes
reported in the literature are larger than this ideal dimension which
limits their applications for the cellular imaging. It is possible to use
NP assemblies composed of smaller NPs so that the overall dimension
of the assembly stays in the ideal window as outlined in reference.
67
Another possibility is to work with small NPs functionalized with
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