Handbook of Biomedical Optics

248 Handbook of Biomedical Optics

instance, detection of calcium dipicolinate from Bacillus subti-

lis

spores (surrogates for anthrax) was accomplished at the 10

−13

M level using SERS substrates consisting of silver lm depos-

ited on nanospheres (Zhang et al. 2005), whereas in spontaneous

Raman, it is unusual to detect a molecule’s presence below the

micromolar level. Figure 12.11 shows a representative spectrum

from this experiment, exhibiting peaks that could never been

observed at such low concentrations using spontaneous, unen-

hanced Raman scattering.

Depending upon the target molecule, however, it can be non-

trivial to achieve consistent ...