10 Super-Resolution Imaging Based on Nonlinear Plasmonic Scattering
243
in fluorescence microscopy arise mainly due to the basic requirement of labelling.
Therefore, it is more than desirable to develop super-resolution label-free imaging
modality based on an alternative contrast agent, such as scattering [23–26].
10.1.2 Plasmonic Nanostructures for Super-Resolution
Microscopy
It is well known that plasmonic nanostructures provide extraordinarily strong scattering, thus ideal for the aim of scattering-based super-resolution imaging [27, 28].
A plasmon is a quantum of collective oscillation of free electrons. It is a quasiparticle
observed at the interface of materials with real negative (such as metals or doped
semiconductors) and real positive (such as dielectrics or air) dielectric constants. The
concentration of electrons is tightly confined to the regions near the nanostructure
surface that leads to enhancement in EM fields. The intensity of the enhanced EM
fields can exceed 10
4 –10
9 of the incident light intensity [27]. Interestingly, these
regions of enhanced fields are confined to volumes much smaller than the diffraction
limit of light. Moreover, plasmonic nanoparticles offer high photo-stability, with near
infinite photon budgets, yielding both high localisation precision and long observation times. Note that plasmonic nanostructure produces strong Rayleigh scattering at
its plasmon resonance and allows single nanoparticles (NPs) to be easily imaged in
an optical microscope. For instance, Rayleigh scattering by an 80 nm gold nanoparticle at surface plasmon resonance (SPR) is about five orders of magnitude higher
than emission from a traditional fluorophore, and thus allows higher localisation
precision [27, 28]. These properties make plasmonic NPs an attractive alternate in
optical super-resolution imaging applications. In addition, it is facilitating to avail the
tunability of the surface plasmon resonance (SPR), which is extremely sensitive to
the size, shape, and composition of the NPs, as well as its local environment [23]. It
is convenient that various facile synthesis routes of plasmonic NPs are well reported
in the literature, including methods for its surface modifications towards higher biocompatibility and low toxicity [29]. Below we briefly review recent literatures on the
combination of plasmonics for super-resolution imaging, based on the same three
super-resolution approaches that we mentioned in the last section.
(a) Objectives modifications (or super-lens): Plasmonic nanostructures can be
explored in the realisation of super-lens and hyper-lens to detect high spatial
frequency information from the sample to improve the overall spatial resolution. Zhang et al. demonstrated this using a thin slab of silver as a super-lens
to image 60 nm features in a sample [30]. After passing through the superlens, the high spatial frequency components again evanescently decay, which
requires that the imaging lens must be placed in the near-field of the plasmonic
super-lens in order to project the image into the far-field. As a super-lens only
243
in fluorescence microscopy arise mainly due to the basic requirement of labelling.
Therefore, it is more than desirable to develop super-resolution label-free imaging
modality based on an alternative contrast agent, such as scattering [23–26].
10.1.2 Plasmonic Nanostructures for Super-Resolution
Microscopy
It is well known that plasmonic nanostructures provide extraordinarily strong scattering, thus ideal for the aim of scattering-based super-resolution imaging [27, 28].
A plasmon is a quantum of collective oscillation of free electrons. It is a quasiparticle
observed at the interface of materials with real negative (such as metals or doped
semiconductors) and real positive (such as dielectrics or air) dielectric constants. The
concentration of electrons is tightly confined to the regions near the nanostructure
surface that leads to enhancement in EM fields. The intensity of the enhanced EM
fields can exceed 10
4 –10
9 of the incident light intensity [27]. Interestingly, these
regions of enhanced fields are confined to volumes much smaller than the diffraction
limit of light. Moreover, plasmonic nanoparticles offer high photo-stability, with near
infinite photon budgets, yielding both high localisation precision and long observation times. Note that plasmonic nanostructure produces strong Rayleigh scattering at
its plasmon resonance and allows single nanoparticles (NPs) to be easily imaged in
an optical microscope. For instance, Rayleigh scattering by an 80 nm gold nanoparticle at surface plasmon resonance (SPR) is about five orders of magnitude higher
than emission from a traditional fluorophore, and thus allows higher localisation
precision [27, 28]. These properties make plasmonic NPs an attractive alternate in
optical super-resolution imaging applications. In addition, it is facilitating to avail the
tunability of the surface plasmon resonance (SPR), which is extremely sensitive to
the size, shape, and composition of the NPs, as well as its local environment [23]. It
is convenient that various facile synthesis routes of plasmonic NPs are well reported
in the literature, including methods for its surface modifications towards higher biocompatibility and low toxicity [29]. Below we briefly review recent literatures on the
combination of plasmonics for super-resolution imaging, based on the same three
super-resolution approaches that we mentioned in the last section.
(a) Objectives modifications (or super-lens): Plasmonic nanostructures can be
explored in the realisation of super-lens and hyper-lens to detect high spatial
frequency information from the sample to improve the overall spatial resolution. Zhang et al. demonstrated this using a thin slab of silver as a super-lens
to image 60 nm features in a sample [30]. After passing through the superlens, the high spatial frequency components again evanescently decay, which
requires that the imaging lens must be placed in the near-field of the plasmonic
super-lens in order to project the image into the far-field. As a super-lens only