502
F. Gentile et al.
14.1 Introduction
Plasmonics is a branch of Physics extremely promising for its applications in
electronics, chemistry, computer science, solar energy harvesting and biology. In
particular, it is dedicated to the investigation of confined electromagnetic waves
originating by the combination of free electrons with the light source. Besides noble
metals, artificial materials are at the basis of Plasmonics. This aspect strictly relates it
to Nanotechnology, a growing science aiming to investigate both the theoretical and
fabrication aspects of devices with dimensions in the nanometer range [1]. The strong
appeal of these systems is their capacity of fundamentally changing the way biomedical sciences are practiced, in that they feature characteristic length scales that are of
the same order of magnitude of biological objects (from cells, as large as ten microns,
to bio molecules sizing few nanometers or less), and can accordingly interact with
these in a fashion that new physical/biological laws, strategies or possibilities emerge
[2]. Many are the examples where nanotechnology is applied to biology and include,
for instance, surfaces patterned with random, rather than periodic, micro- nano- fabricated themes, to guide cells attachment and proliferation [3]; needles, holes or
micro- nano- based microfluid channels for transdermal drug administration, protein
sorting and cell analysis [4]; microstuctured, three dimensional scaffolds for tissue
engineering [5]; the nano particles toolbox for the smart delivery of drugs and imaging [6, 7]; devices for molecular detection, identification and diagnostics. The latter
comprise a variety of different systems, including nanowires and nano-cantilevers,
microarrays [8], and nanoporous silicon surfaces, whereby the species of interest
can be selectively adsorbed and detected using MALDI TOF mass spectroscopy
techniques [9].
Early detection is particularly important in the case of cancer and other pathologies,
in that the early stages of disease are typically treated with the greatest probability of
success [10, 11]. Albeit the large variety of systems listed above, surface enhanced
Raman scattering (SERS) substrates are among the most promising in terms of sensitivity, reproducibility and reliability [12]. These nano geometry based devices are
capable to detect biological moieties in the limits of very low abundance ranges, and
offer the most effective way for the diagnosis of few, or single, molecules.
SERS effects stem from the combination of subwavelength nanoscale features and
noble metals, and particularly from the excitation of localized surface plasmons at
the interface with a metallic surface, and thus they strongly depend upon the topology
of the active substrate. It is very well understood that certain regular geometries, with
a convenient design, induce giant electric fields, with an enhancement of up to 10 9
in the Raman signal. Recent advances in SERS technology produced, for instance,
periodic arrays of metallic nano dots [13]; adiabatic nanofocusing cones [14–20];
or groups of three hierarchical metallic hemi spheres, where the ratio between the
diameters or, equivalently, the distances of the spheres is chosen with high precision,
and these are called nano lenses [21]. Interestingly, randomly rough surfaces, with a
roughness in a nanometric scale, also exhibit superior sensing capabilities [22] but,
differently from regular geometries, they retain the advantages of short fabrication
F. Gentile et al.
14.1 Introduction
Plasmonics is a branch of Physics extremely promising for its applications in
electronics, chemistry, computer science, solar energy harvesting and biology. In
particular, it is dedicated to the investigation of confined electromagnetic waves
originating by the combination of free electrons with the light source. Besides noble
metals, artificial materials are at the basis of Plasmonics. This aspect strictly relates it
to Nanotechnology, a growing science aiming to investigate both the theoretical and
fabrication aspects of devices with dimensions in the nanometer range [1]. The strong
appeal of these systems is their capacity of fundamentally changing the way biomedical sciences are practiced, in that they feature characteristic length scales that are of
the same order of magnitude of biological objects (from cells, as large as ten microns,
to bio molecules sizing few nanometers or less), and can accordingly interact with
these in a fashion that new physical/biological laws, strategies or possibilities emerge
[2]. Many are the examples where nanotechnology is applied to biology and include,
for instance, surfaces patterned with random, rather than periodic, micro- nano- fabricated themes, to guide cells attachment and proliferation [3]; needles, holes or
micro- nano- based microfluid channels for transdermal drug administration, protein
sorting and cell analysis [4]; microstuctured, three dimensional scaffolds for tissue
engineering [5]; the nano particles toolbox for the smart delivery of drugs and imaging [6, 7]; devices for molecular detection, identification and diagnostics. The latter
comprise a variety of different systems, including nanowires and nano-cantilevers,
microarrays [8], and nanoporous silicon surfaces, whereby the species of interest
can be selectively adsorbed and detected using MALDI TOF mass spectroscopy
techniques [9].
Early detection is particularly important in the case of cancer and other pathologies,
in that the early stages of disease are typically treated with the greatest probability of
success [10, 11]. Albeit the large variety of systems listed above, surface enhanced
Raman scattering (SERS) substrates are among the most promising in terms of sensitivity, reproducibility and reliability [12]. These nano geometry based devices are
capable to detect biological moieties in the limits of very low abundance ranges, and
offer the most effective way for the diagnosis of few, or single, molecules.
SERS effects stem from the combination of subwavelength nanoscale features and
noble metals, and particularly from the excitation of localized surface plasmons at
the interface with a metallic surface, and thus they strongly depend upon the topology
of the active substrate. It is very well understood that certain regular geometries, with
a convenient design, induce giant electric fields, with an enhancement of up to 10 9
in the Raman signal. Recent advances in SERS technology produced, for instance,
periodic arrays of metallic nano dots [13]; adiabatic nanofocusing cones [14–20];
or groups of three hierarchical metallic hemi spheres, where the ratio between the
diameters or, equivalently, the distances of the spheres is chosen with high precision,
and these are called nano lenses [21]. Interestingly, randomly rough surfaces, with a
roughness in a nanometric scale, also exhibit superior sensing capabilities [22] but,
differently from regular geometries, they retain the advantages of short fabrication