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L. D. Negro et al.
imprint process begins by heating the Au covered master to 90 ◦ C, when it is then
pressed onto the surface of the silk layer with a force of 50 kg (area of 16 mm 2 ) for
5 min. During the imprinting, the plasmonic nanostructures bind to the surface of
silk layer. Upon completion of the bonding cycle, the master is removed, leaving the
Au embedded on the surface of the silk layer as shown in Fig. 9.14d for nano-dots
arrays. Nano-imprinted plasmonic hole arrays with Vogel spiral geometry are shown
as an example in Fig. 9.14e.
A similar process has been successfully developed to imprint arrays of metallic
nanoparticles atop polymer films. In this case, a Si mold consisting of nanopillar
arrays needs to be utilized. More details on these novel high throughput and scalable
fabrication processes can be found in Ref. [98]. These techniques enable the largescale replication of arbitrarily complex nanostructures with deep sub-wavelength
details down to 30 nm with a high throughput, as the mould is reusable. The inexpensive scalability of aperiodic nanoplasmonic structures over large areas is of great
importance for device engineering as it offers the opportunity to abate fabrication
costs and to develop aperiodic substrates into a mature technology. Some specific
device applications of aperiodic nanoplasmonic substrates will be discussed in the
next sections.
9.3.2 Applications to Surface Enhanced Raman Biosensing
Surface Enhanced Raman Scattering (SERS) spectroscopy is a well-established and
highly sensitive technique for investigating the specific vibrational response of a
variety of different analytes with fingerprinting accuracy. Recently, SERS spectroscopy has been successfully applied to label-free chemical and biological sensing
[99–101], where it has proven to be an excellent method for sensing DNA hybridization [102], protein binding events [103], and even single molecules [104–107]. In
addition, it bears great promises for rapid identification of viruses and bacteria
[108–110], potentially enabling whole-organism fingerprinting. The dramatic enhancement of the Raman scattering efficiency observed in SERS experiments is mainly
driven by the enhanced local electromagnetic fields in nanostructured metal surfaces
[111–113]. In fact, despite that SERS enhancement can also be affected by the specific electronic resonances of Raman-active molecules (i.e., electronic enhancement)
and by their direct contact with metal surfaces (i.e., chemical enhancement), the dominant factor originates from a resonant effect between the incident and the scattered
radiation fields associated to the excitation of localized surface plasmon resonances.
In particular, the Raman enhancement factor scales roughly as the fourth power of
the local field [100, 111, 112]:
δ SE RS ∝
E loc (λ p )
2
E loc (λ s )
2
(9.10)
L. D. Negro et al.
imprint process begins by heating the Au covered master to 90 ◦ C, when it is then
pressed onto the surface of the silk layer with a force of 50 kg (area of 16 mm 2 ) for
5 min. During the imprinting, the plasmonic nanostructures bind to the surface of
silk layer. Upon completion of the bonding cycle, the master is removed, leaving the
Au embedded on the surface of the silk layer as shown in Fig. 9.14d for nano-dots
arrays. Nano-imprinted plasmonic hole arrays with Vogel spiral geometry are shown
as an example in Fig. 9.14e.
A similar process has been successfully developed to imprint arrays of metallic
nanoparticles atop polymer films. In this case, a Si mold consisting of nanopillar
arrays needs to be utilized. More details on these novel high throughput and scalable
fabrication processes can be found in Ref. [98]. These techniques enable the largescale replication of arbitrarily complex nanostructures with deep sub-wavelength
details down to 30 nm with a high throughput, as the mould is reusable. The inexpensive scalability of aperiodic nanoplasmonic structures over large areas is of great
importance for device engineering as it offers the opportunity to abate fabrication
costs and to develop aperiodic substrates into a mature technology. Some specific
device applications of aperiodic nanoplasmonic substrates will be discussed in the
next sections.
9.3.2 Applications to Surface Enhanced Raman Biosensing
Surface Enhanced Raman Scattering (SERS) spectroscopy is a well-established and
highly sensitive technique for investigating the specific vibrational response of a
variety of different analytes with fingerprinting accuracy. Recently, SERS spectroscopy has been successfully applied to label-free chemical and biological sensing
[99–101], where it has proven to be an excellent method for sensing DNA hybridization [102], protein binding events [103], and even single molecules [104–107]. In
addition, it bears great promises for rapid identification of viruses and bacteria
[108–110], potentially enabling whole-organism fingerprinting. The dramatic enhancement of the Raman scattering efficiency observed in SERS experiments is mainly
driven by the enhanced local electromagnetic fields in nanostructured metal surfaces
[111–113]. In fact, despite that SERS enhancement can also be affected by the specific electronic resonances of Raman-active molecules (i.e., electronic enhancement)
and by their direct contact with metal surfaces (i.e., chemical enhancement), the dominant factor originates from a resonant effect between the incident and the scattered
radiation fields associated to the excitation of localized surface plasmon resonances.
In particular, the Raman enhancement factor scales roughly as the fourth power of
the local field [100, 111, 112]:
δ SE RS ∝
E loc (λ p )
2
E loc (λ s )
2
(9.10)