Biomedical Engineering Reference
In-Depth Information
applies to the biomolecules present on the cell wall or cell membrane
of the microorganism but the technique is not immune to interference
from a large number of biomolecules used in the bacteria culture.
This points out the short fall of the label-free detection.
(
)
Figure 11.4
Raman (black) and SERS (blue) spectra of
Staphylococcus
aureus
cells. Left inset, a small cluster of
S. aureus
cells. Right
inset,
S. aureus
cells incubated with colloidal Ag sol. The cells
are well decorated with Ag NPs. SERS spectra of
S.
aureus
cells
shows a distinct sugar vibration at 1330 cm
−1
. Cell Raman
and SERS spectra were acquired with 60 and 1 s acquisition
time, respectively. See also Color Insert.
In the labeled detection scheme, a Raman active reporter
molecule is adsorbed on the surface of NPs that are co-functionalized
with recognition (e.g., antibody) and passivation molecules to
enable detection of a speciic target and reduce nonspeciic bonding
events with unwanted biomolecules as shown in the schematics of
Fig. 11.5B. There are large number of examples of SERS-labeled
detection with target species including neurotransmitters,
43
nucleic acids,
44,45
proteins,
46-49
enzymes,
50-53
cellular organelles,
54
microbes,
55,56
spores,
57-59
and diseased cells.
60-62
As very high
SERS enhancements are attainable through small NP aggregates,
it is desirable to design functional SERS NP assemblies with such
SERS “hot spots” built into each unit.
55
This approach relies on a
controlled aggregation of NPs that are subsequently protected with
either passivation molecules or inorganic shells. This approach
is particularly suitable when designing multiplexed experiments
in which multiple targets are to be identiied with different SERS
probes carrying different Raman labels.
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