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sFTIR, Raman, and SERS Imaging of Fungal Cells 143

dielectric constant, ε is the dielectric constant and q is the volume
0
72
fraction in the metal particle. This theory was already being developed
to explain the colors seen on anodized aluminum, following
electrolysis in inorganic salt solutions, and had been shown to be
understandable in terms of colloidal particles embedded within the
thin dielectric medium. 73
The intensity of a mode in SERS scatter depends not only on the
normal vibrational mode, but also on the orientation of the molecule
relative to the surface of the particle, with molecules that are per-
pendicular to the surface receiving the maximum enhancement.
Additional influences in SERS scatter include the possibility of
chemical bonding to the surface, charge transfer between the molecule
and the surface, and proximity of the exciting laser energy to an
electronic absorption of the molecule; the latter would give rise to
SERRS, discussed below.
Because of the importance of this discovery, and because the phys-
ical explanation for the phenomenon remains incomplete, numerous
review articles have appeared in the last 5 years, delineating some of
1–7
the evolving theories and related practical applications. It is not
within the scope or goals of the present article to parse these in detail;
some of the major points are provided here with references for the
interested reader. Before beginning, it is interesting to note the number
of papers that self-identify as being concerned with “SERS” and “imag-
ing” has only very recently begun to take off (Fig. 5.10).
The vast majority employ SERS imaging techniques based on
nanodots, whether inserted into or taken up by cells whilst alive,
or used as tethered tags. 2,6,74,75 The nanodot serves the role of
chromophore and reports on the particular site for which it has

40
Papers per Year “SERS” and “Imaging” 20

30

10

0
1978 1988 1998 2008
Year

FIGURE 5.10 Number of papers per year that are self-identifi ed as being
concerned with both SERS and imaging from 1978 to 2008.