J. Bukowska and P. Piotrowski
30
spectroscopy are visible or near infrared lasers. Another, more advanced possibility to increase the Raman scattering intensity is the use of non-linear effects such
as stimulated Raman scattering. however, the most effective way of amplification
of the Raman scattering is offered by surface enhanced Raman scattering (SERS)
spectroscopy. In SERS, Raman signal may be enhanced by as much as 11 orders
of magnitude. typical SERS enhancement factors are of order of 10
4
–10
6
. Further
enhancement of the Raman spectrum is obtained when the laser excitation energy
corresponds to electronic transition of the molecule (resonance Raman). In this effect, called surface enhanced resonance Raman scattering (SERRS), enhancement
factors can reach 10
11
, allowing detection at a single molecule level. Combined
enhancement processes provide a Raman signal of sensitivity at least equivalent or
even higher than that of fluorescence. very high sensitivity, selectivity and ability
to identify molecular species, together with other advantages make SERS/SERRS
spectroscopy an exceptionally attractive tool for variety of applications in bioscience. SERS may compete successfully with other spectroscopic methods in bioscience, such as fluorescence.
giant amplification of the Raman signal in SERS is generated by metallic
nanoparticles (typically silver, gold and copper), on which target molecules are
adsorbed. the first surface-enhanced Raman spectrum of pyridine adsorbed on a
silver electrode was observed by Fleischmann and coworkers in 1974 [1] at the
university of Southampton, but in fact they did not recognize the importance of
their results. the first explanation of this new phenomenon in terms of a giant surface enhancement of the Raman scattering, observed by Fleischmann et al., was
reported by Jeanmaire and van duyne in 1977 [2]. Since 1977, many papers on both
theoretical and practical aspects of SERS spectroscopy have been published. In the
last several years, popularity of surface-enhanced Raman spectroscopy has grown
rapidly. Among a great variety of applications, these connected with biomolecule
detection develop extremely quickly.
3.2 SERS Phenomenon—Background and Mechanism of
Enhancement
Phenomena concerning interactions between matter and light might be roughly divided into three cases: absorption and emission of light, scattering—when, as opposed to emission, angle distribution of radiated photons is observed—and reflection, when the wave vector changes its direction at an interface between two media
according to the laws of reflection. Raman effect falls into the second category
and is defined more accurately as inelastic scattering of light, which means that
the energy of the scattered photons differs from the incident ones. thanks to this
energy difference, Raman spectroscopy informs us about energies of rotational and
vibrational modes of the studied molecule. Raman spectrum contains a set of bands,
which is characteristic for a given molecule, thus identifies the sample, providing
its so called chemical fingerprint.
30
spectroscopy are visible or near infrared lasers. Another, more advanced possibility to increase the Raman scattering intensity is the use of non-linear effects such
as stimulated Raman scattering. however, the most effective way of amplification
of the Raman scattering is offered by surface enhanced Raman scattering (SERS)
spectroscopy. In SERS, Raman signal may be enhanced by as much as 11 orders
of magnitude. typical SERS enhancement factors are of order of 10
4
–10
6
. Further
enhancement of the Raman spectrum is obtained when the laser excitation energy
corresponds to electronic transition of the molecule (resonance Raman). In this effect, called surface enhanced resonance Raman scattering (SERRS), enhancement
factors can reach 10
11
, allowing detection at a single molecule level. Combined
enhancement processes provide a Raman signal of sensitivity at least equivalent or
even higher than that of fluorescence. very high sensitivity, selectivity and ability
to identify molecular species, together with other advantages make SERS/SERRS
spectroscopy an exceptionally attractive tool for variety of applications in bioscience. SERS may compete successfully with other spectroscopic methods in bioscience, such as fluorescence.
giant amplification of the Raman signal in SERS is generated by metallic
nanoparticles (typically silver, gold and copper), on which target molecules are
adsorbed. the first surface-enhanced Raman spectrum of pyridine adsorbed on a
silver electrode was observed by Fleischmann and coworkers in 1974 [1] at the
university of Southampton, but in fact they did not recognize the importance of
their results. the first explanation of this new phenomenon in terms of a giant surface enhancement of the Raman scattering, observed by Fleischmann et al., was
reported by Jeanmaire and van duyne in 1977 [2]. Since 1977, many papers on both
theoretical and practical aspects of SERS spectroscopy have been published. In the
last several years, popularity of surface-enhanced Raman spectroscopy has grown
rapidly. Among a great variety of applications, these connected with biomolecule
detection develop extremely quickly.
3.2 SERS Phenomenon—Background and Mechanism of
Enhancement
Phenomena concerning interactions between matter and light might be roughly divided into three cases: absorption and emission of light, scattering—when, as opposed to emission, angle distribution of radiated photons is observed—and reflection, when the wave vector changes its direction at an interface between two media
according to the laws of reflection. Raman effect falls into the second category
and is defined more accurately as inelastic scattering of light, which means that
the energy of the scattered photons differs from the incident ones. thanks to this
energy difference, Raman spectroscopy informs us about energies of rotational and
vibrational modes of the studied molecule. Raman spectrum contains a set of bands,
which is characteristic for a given molecule, thus identifies the sample, providing
its so called chemical fingerprint.