Surface-Enhanced Raman Scattering Based on Noble Metal Nanoparticles - From Bioimaging to Biosensors: Noble Metal Nanoparticles in Biodetection - page 261

the desired antigen. Protein A is a virulence factor which is naturally
expressed on the cell wall of S. aureus in great abundance (tens of
thousands/cell). 63 It is highly speciic to the S. aureus species and
thus serves as a key marker for this pathogen. A small protein unit,
single domain antibody (sdAb), derived by panning a V H phage
display library against protein A 64,65 is conjugated onto the silica
shell of NAEB which enables target-speciic recognition (Fig. 11.5B).
Raman imaging of the S. aureus cells treated with sdAb-NAEB is
shown in Fig. 11.7. Here, two sets of sdAb-NAEB-labeled S. aureus
cells are visible in the SEM image of Fig. 11.7A. The upper set
consists of a group of 3 cells while the lower set is a single cell. Both
sets of cells were well decorated with sdAb-NAEB which is indicative
of the positive binding response between the sdAb-NAEB and the
targeted pathogen. An optical image of the same area is shown in
Fig. 11.7B. The false-colored Raman intensity map (Fig. 11.7C)
is constructed from the integrated intensity of the 1196 cm −1 and
1238 cm −1 vibrational bands of R6G. Two bright regions were
observed in the Raman intensity maps, demonstrating good spatial
correlation to the cells observed in the optical (Fig. 11.7B) and SEM
(Fig. 11.7A) images. Figure 11.7D is a full SERS spectrum of the R6G-
NAEB taken from the single cell (lower bright spot) region. The single
cell from the Raman intensity map is clearly resolved and detected
through sdAb-NAEB labeling. The speciicity of the sdAb and the
ultrahigh sensitivity of NAEB render targeted detection of S. aureus
at single cell level easily attainable.

(A) (C)

(B)

(D)

μ

μ μ

( )

Figure 11.7 SEM (A), Optical (B), and SERS intensity map (C) of NAEB-
labeled S. aureus cells. (D) SERS spectrum of a single
S. aureu s cell labeled with NAEB. Reproduced from Ref. 56
with permission. See also Color Insert.

It is possible to introduce different reporter molecules into
NAEB and couple it with different antibodies to enable multiplexed
detection of different types of pathogen. However, in such operations,