120
K. Kneipp et al.
structural information on the environment of the label [86]. Moreover, the SERS
signature of a reporter molecule, attached to the gold nanoparticle, which exhibits
a pH-sensitive Raman spectrum, can deliver information on the local pH-value in
the surrounding of the label [87]. SERS labels can be functionalized (targeting unit)
using specific linker in order to address specific molecules or structures.
Due to the plasmonic support, SERS appears at high signal level. This suggests
SERS signatures for vibrational imaging.
Two-photon excitation is gaining rapidly in interest and significance in spectroscopy and optical imaging. The development of optical labels that are suitable also
for two-photon excitation and non-linear imaging is an important task in advancing methods for vibrational probing and imaging. Effective plasmonic supported
cross sections of SERS and SEHRS can be on the order of 10 −17 − 10 −16 cm 2 and
10 −46 − 10 −45 cm 4 s, respectively. This suggests versatile optical SERS/ SEHRS
labels suitable for both one- and two-photon probing and imaging. Figure 2.8 shows
the schematic of a SEHRS/SERS label along with its spectral signatures, for this
label, SEHRS and SERS spectra of the reporter molecule rose bengal. Plasmonic
supported Raman labels have also been employed in CARS imaging for immunohistochemistry [50].
2.5 Brief Summary and Outlook
Plasmonics supported vibrational spectroscopy can transform vibrational spectroscopy from a method for chemical structural analysis requiring relatively large
amounts of matter to a tool for nanosciences providing at the same time high
molecular structural selectivity and ultrasensitive detection limits. Vibrational spectra collected by surface enhanced Raman scattering (SERS), by surface enhanced
infrared absorption (SEIRA), and by surface enhanced two-photon excited hyper
Raman scattering (SEHRS) allow a comprehensive structural characterization of
matter and monitoring of chemical processes. Sophisticated nanoantenna structures
and arrays advance the field of surface enhanced IR absorption. Here, the extension
to the THz range might be of particular interest. A combination of the confined
probed volumes and the enhancement of vibratinal signatures in plasmonic fields
with scanning probe capabilities of an atomic force microscope as it is employed in
tip enhanced Raman spectroscopy enables simultaneous morphological-topological
and molecular structural information at the nanoscale.
In particular, non-linear coherent and incoherent Raman scattering benefits from
plasmonic support. Further progress in theoretical understanding of plasmonic
enhancement as well as advanced technologies for making taylored plasmonic nanostructures will allow us to take advantage of all the potential capabilities of plasmonic
supported non-linear vibrational spectroscopy. First observation of surface enhanced
femtosecond stimulated Raman scattering opens up exciting new ways for probing
ultrafast processes that might occur in plasmon-mediated interaction between molecules and light. Methods such as SEHRS, SEPARS and SECARS combine structural
K. Kneipp et al.
structural information on the environment of the label [86]. Moreover, the SERS
signature of a reporter molecule, attached to the gold nanoparticle, which exhibits
a pH-sensitive Raman spectrum, can deliver information on the local pH-value in
the surrounding of the label [87]. SERS labels can be functionalized (targeting unit)
using specific linker in order to address specific molecules or structures.
Due to the plasmonic support, SERS appears at high signal level. This suggests
SERS signatures for vibrational imaging.
Two-photon excitation is gaining rapidly in interest and significance in spectroscopy and optical imaging. The development of optical labels that are suitable also
for two-photon excitation and non-linear imaging is an important task in advancing methods for vibrational probing and imaging. Effective plasmonic supported
cross sections of SERS and SEHRS can be on the order of 10 −17 − 10 −16 cm 2 and
10 −46 − 10 −45 cm 4 s, respectively. This suggests versatile optical SERS/ SEHRS
labels suitable for both one- and two-photon probing and imaging. Figure 2.8 shows
the schematic of a SEHRS/SERS label along with its spectral signatures, for this
label, SEHRS and SERS spectra of the reporter molecule rose bengal. Plasmonic
supported Raman labels have also been employed in CARS imaging for immunohistochemistry [50].
2.5 Brief Summary and Outlook
Plasmonics supported vibrational spectroscopy can transform vibrational spectroscopy from a method for chemical structural analysis requiring relatively large
amounts of matter to a tool for nanosciences providing at the same time high
molecular structural selectivity and ultrasensitive detection limits. Vibrational spectra collected by surface enhanced Raman scattering (SERS), by surface enhanced
infrared absorption (SEIRA), and by surface enhanced two-photon excited hyper
Raman scattering (SEHRS) allow a comprehensive structural characterization of
matter and monitoring of chemical processes. Sophisticated nanoantenna structures
and arrays advance the field of surface enhanced IR absorption. Here, the extension
to the THz range might be of particular interest. A combination of the confined
probed volumes and the enhancement of vibratinal signatures in plasmonic fields
with scanning probe capabilities of an atomic force microscope as it is employed in
tip enhanced Raman spectroscopy enables simultaneous morphological-topological
and molecular structural information at the nanoscale.
In particular, non-linear coherent and incoherent Raman scattering benefits from
plasmonic support. Further progress in theoretical understanding of plasmonic
enhancement as well as advanced technologies for making taylored plasmonic nanostructures will allow us to take advantage of all the potential capabilities of plasmonic
supported non-linear vibrational spectroscopy. First observation of surface enhanced
femtosecond stimulated Raman scattering opens up exciting new ways for probing
ultrafast processes that might occur in plasmon-mediated interaction between molecules and light. Methods such as SEHRS, SEPARS and SECARS combine structural