Surface-Enhanced Raman Scattering-Based Bioimaging - Nanotechnology for Biomedical Imaging and Diagnostics - page 325

spectra per minute, 30 times faster than point mapping approach. Moreover, the
power density on any one area of the sample is reduced by a factor of 40-60 times
due to the defocusing of laser and rapid scanning compared to an equivalent
response in point mapping.

11.4 In VITRo and In VIVo raman-BaSed Bioimaging

SERS-based bioimaging can be broadly classified into two types: labeled and label-
free. in the label-free approach, plasmonic nanostructures are employed to enhance
the intrinsic Raman signal of the biological species under investigation. on the other
hand, labeled approach involves the use of exogenous contrast, which is directed to
the target biological species either by active or passive targeting followed by their
mapping (or detection).

11.4.1 Label-free SerS-Based Bioimaging

for label-free SERS-based assays, biomolecules (analytes) directly locate on or in
close proximity to a nanostructured metal surface and thus are recognized by their
enhanced Raman signals without external labels needed. Detection can be achieved
with the use of individual or assembled plasmonic nanoparticles, which exhibit
intense local EM fields. We would like to highlight a recent report that the molec-
ular changes of cell components, such as the nucleus, could be monitored during
the different phased of its full cell cycle by its Rayleigh images and Raman vibra-
tion spectra in real time [31]. figure 11.4 showed that the different phases of the
cell cycle could be identified based on the Raman peaks attributed to Dna and
protein. The label-free approach is simple and can provide molecular information
about target cells, but signals can often be complicated due to the interference from
the surrounding cellular matrix or impurities whose Raman signals could also be
enhanced.

11.4.2 Labeled SerS-Based Bioimaging

The other type of SERS-based bioimaging involves plasmonic nanoparticles adsorbed
or covalently conjugated with Raman reporters (molecules with large Raman cross
sections), which serve as exogenous contrast agents. The labeled approach is highly
specific because it exhibits little to no signal interference from other Raman-active
species as the SERS enhancement decays exponentially from the surface of the
nanoparticles, making any other contributions virtually undetectable compared to the
Raman-active molecules adsorbed on the nanoparticle surface. gold nanostructures
with Raman reporters (called SERS probes henceforth) have been extensively inves-
tigated for cancer [18, 32-35] and other disease [36, 37] biomarker detection, as well
as bacterial [38-41] and viral [42, 43] microorganism [42-44] detection.
common with any other optical bioimaging modality, which employs exogenous
contrast agents, ultrabright probes are paramount for deep and high-resolution