3 Surface-enhanced Raman Scattering ...
35
Ag or Au nanoparticles from the colloid suspension. this strategy was first demonstrated by Chumanov et al. in 1995 [14] and developed by group of Natan et al.
[15]. the idea of depositing metal nanoparticles from colloidal suspensions was
also successfully applied to the fabrication of three-dimensional (3-d) structures of
NP at the solid substrates by repeating chemical binding of the subsequent layers of
NP deposit [16–18]. Another way is immobilization of NP by electrostatic attraction
of the charged metal particles by oppositely charged solid support. In this strategy
the most popular method is covering the solid substrate with positively charged derivatized silanes (e.g. aminopropyltrimethoxysilane) [14] or polymer layer such as
poly(diallydimethylammonium chloride), which, as a positively charged polymer,
is able to attract the negatively charged colloids [19] or polylysine [20]. Another,
less common substrates include surfaces roughened by chemical treatment of solid
substrate [21], “island films” deposited on glass and films deposited by evaporation
or sputtering substrates [22, 23].
metallic nanoparticles or other nanostructures can be also fabricated directly
on the surface of the solid support using advanced physical methods such as nanolithography [24–28] or micro-contact printing [29]. thin films of silver or gold
can be also vapor-deposited over polystyrene or silica nanospheres of controlled
diameter (FoN-film over nanospheres), deposited on solid substrate. this method
results in highly reproducible and effective supports [30, 31]. using this technique,
van duyne group developed interesting SERS support by removing the underlying
nanosphere mask, thus leaving periodic structure of metal nanoparticles (Fig. 3.2e),
deposited on the free space between the nanospheres. As reported [32], supports
prepared in this way exhibit very high enhancement factors (of order 10
8
).
Plasmonic properties of metal nanoparticles can be significantly changed by tailoring their shape or size. Numerous methods of production of shaped nanoparticles
such as nanorods [34, 35] triangles [36], nanocubes [37, 38], polyhedrons [39], stars
[40–42] and nanoflowers [43] have been developed. Some of these nanostructures
exhibit higher enhancement factors as compared to nanospheres, because of the
presence of sharp edges and corners that are able to concentrate extremely strong
electromagnetic fields (see Fig. 3.1). Among a great variety of nanoparticles, hollow spheres with differing cavity diameter—which allows tuning the plasmon properties—are very effective enhancers [44].
the possibility of shifting plasmon resonance to the near infrared is sometimes
important in biological applications, because of problems with surface photochemistry when using visible radiation (especially on silver) and/or problems with fluorescence background. this red-shift may be also achieved in core-shell nanoparticles built of a spherical silica core of varying dimensions, covered with a thin
metal shell [45, 46]. It was confirmed that spherical Au nanoshells, in which plasmon resonance frequencies are controlled by the relative inner and outer radius of
the metallic shell layer (see Fig. 3.3), can be used as an effective and reproducible
SERS substrate, also for large biomolecules and more complex systems such as
dNA and living cells [47–50].
Interesting SERS substrate has been developed by tian group [52, 53]. they
coated Au nanoparticles with a very thin (2–3 nm) silica film that isolates the metal
35
Ag or Au nanoparticles from the colloid suspension. this strategy was first demonstrated by Chumanov et al. in 1995 [14] and developed by group of Natan et al.
[15]. the idea of depositing metal nanoparticles from colloidal suspensions was
also successfully applied to the fabrication of three-dimensional (3-d) structures of
NP at the solid substrates by repeating chemical binding of the subsequent layers of
NP deposit [16–18]. Another way is immobilization of NP by electrostatic attraction
of the charged metal particles by oppositely charged solid support. In this strategy
the most popular method is covering the solid substrate with positively charged derivatized silanes (e.g. aminopropyltrimethoxysilane) [14] or polymer layer such as
poly(diallydimethylammonium chloride), which, as a positively charged polymer,
is able to attract the negatively charged colloids [19] or polylysine [20]. Another,
less common substrates include surfaces roughened by chemical treatment of solid
substrate [21], “island films” deposited on glass and films deposited by evaporation
or sputtering substrates [22, 23].
metallic nanoparticles or other nanostructures can be also fabricated directly
on the surface of the solid support using advanced physical methods such as nanolithography [24–28] or micro-contact printing [29]. thin films of silver or gold
can be also vapor-deposited over polystyrene or silica nanospheres of controlled
diameter (FoN-film over nanospheres), deposited on solid substrate. this method
results in highly reproducible and effective supports [30, 31]. using this technique,
van duyne group developed interesting SERS support by removing the underlying
nanosphere mask, thus leaving periodic structure of metal nanoparticles (Fig. 3.2e),
deposited on the free space between the nanospheres. As reported [32], supports
prepared in this way exhibit very high enhancement factors (of order 10
8
).
Plasmonic properties of metal nanoparticles can be significantly changed by tailoring their shape or size. Numerous methods of production of shaped nanoparticles
such as nanorods [34, 35] triangles [36], nanocubes [37, 38], polyhedrons [39], stars
[40–42] and nanoflowers [43] have been developed. Some of these nanostructures
exhibit higher enhancement factors as compared to nanospheres, because of the
presence of sharp edges and corners that are able to concentrate extremely strong
electromagnetic fields (see Fig. 3.1). Among a great variety of nanoparticles, hollow spheres with differing cavity diameter—which allows tuning the plasmon properties—are very effective enhancers [44].
the possibility of shifting plasmon resonance to the near infrared is sometimes
important in biological applications, because of problems with surface photochemistry when using visible radiation (especially on silver) and/or problems with fluorescence background. this red-shift may be also achieved in core-shell nanoparticles built of a spherical silica core of varying dimensions, covered with a thin
metal shell [45, 46]. It was confirmed that spherical Au nanoshells, in which plasmon resonance frequencies are controlled by the relative inner and outer radius of
the metallic shell layer (see Fig. 3.3), can be used as an effective and reproducible
SERS substrate, also for large biomolecules and more complex systems such as
dNA and living cells [47–50].
Interesting SERS substrate has been developed by tian group [52, 53]. they
coated Au nanoparticles with a very thin (2–3 nm) silica film that isolates the metal