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S. E. H. Murph and E. Searles
plasmon of the nanoparticles and surface plasmon of the gold substrate, generates
surface-enhanced Raman scattering “hot spots” [25].
A better matching of the laser wavelength with the plasmon band of the newly
aggregates may also be responsible for these responses [25, 26]. Recent studies have
reported that the plasmon field of nanoparticle could be distorted when a dielectric medium around a nanoparticle is changed anisotropically leading to shifting
of the plasmonic absorption and scattering spectra [28]. Typically, this can occur
when nanoparticles are placed on substrates of different compositions or when
functionalized with other moieties.
It was also found that the Raman frequency of 4-mercaptophenol at ≈1100 cm
−1
slightly shifts ~10 cm
−1 and/or split in two different peaks when functionalized on
the composite gold–iron nanomaterials. A peak shift was reported by others when
analytes were captured on metallic nanoparticles and was attributed to a charge
transfer or local bonding effects which could alter the energies of the vibrational and
electronic Raman modes [3, 29].
Ultimately, Raman spectroscopy provided preliminary results of limited levels
of enhancement from the presence of gold plasmonic particles both on iron oxide
supports and independently in solution. The greater increase in signal found in the
presence of iron oxide composite may be attributed to the formation of hot spots
on the surface of the iron oxide creating nano-gaps at the junctions between gold
nanospheres. This technique of the formation of hot-spots junctions and nano-gaps
on the magnetic surface of iron oxide needs further investigation. However, this is
the first study to investigate the creation and use of nano-gap junctions on composite
nanostructures. Moreover, the novel multi-seed-mediated approach was successfully
developed here allowing the creation of iron oxide nanoparticles with increased
amount of plasmonic gold nanospheres. Further studies should focus on tailoring
the nano-gap formation along with completely elucidating the enhanced Raman
scattering mechanism through magnetic manipulation.
Conclusions
Multifunctional composite nanostructures with plasmonic (Au nanoparticles) and
magnetic (Fe 2 O 3 nanoparticles) properties were reproducibly synthesized through a
multi-seed-mediated approach. Iron oxide–gold loading was significantly increased
through the use of seeds during the citrate reduction reaction with a 43% increase
in gold loading from the original seeds to those seeded four times. The resulting
nanocomposite material retains the properties of both individual components: (a)
magnetic Fe 2 O 3 properties and (b) plasmonic Au nanostructures.
Composite structures with plasmonic and magnetic properties provide unique
characteristics from bulk material including the localized surface plasmon bands
and ability for magnetic manipulation to allow the recyclability of the nanoparticle
structure for use in future reactions, reducing cost and use of precious metals such
as gold.
S. E. H. Murph and E. Searles
plasmon of the nanoparticles and surface plasmon of the gold substrate, generates
surface-enhanced Raman scattering “hot spots” [25].
A better matching of the laser wavelength with the plasmon band of the newly
aggregates may also be responsible for these responses [25, 26]. Recent studies have
reported that the plasmon field of nanoparticle could be distorted when a dielectric medium around a nanoparticle is changed anisotropically leading to shifting
of the plasmonic absorption and scattering spectra [28]. Typically, this can occur
when nanoparticles are placed on substrates of different compositions or when
functionalized with other moieties.
It was also found that the Raman frequency of 4-mercaptophenol at ≈1100 cm
−1
slightly shifts ~10 cm
−1 and/or split in two different peaks when functionalized on
the composite gold–iron nanomaterials. A peak shift was reported by others when
analytes were captured on metallic nanoparticles and was attributed to a charge
transfer or local bonding effects which could alter the energies of the vibrational and
electronic Raman modes [3, 29].
Ultimately, Raman spectroscopy provided preliminary results of limited levels
of enhancement from the presence of gold plasmonic particles both on iron oxide
supports and independently in solution. The greater increase in signal found in the
presence of iron oxide composite may be attributed to the formation of hot spots
on the surface of the iron oxide creating nano-gaps at the junctions between gold
nanospheres. This technique of the formation of hot-spots junctions and nano-gaps
on the magnetic surface of iron oxide needs further investigation. However, this is
the first study to investigate the creation and use of nano-gap junctions on composite
nanostructures. Moreover, the novel multi-seed-mediated approach was successfully
developed here allowing the creation of iron oxide nanoparticles with increased
amount of plasmonic gold nanospheres. Further studies should focus on tailoring
the nano-gap formation along with completely elucidating the enhanced Raman
scattering mechanism through magnetic manipulation.
Conclusions
Multifunctional composite nanostructures with plasmonic (Au nanoparticles) and
magnetic (Fe 2 O 3 nanoparticles) properties were reproducibly synthesized through a
multi-seed-mediated approach. Iron oxide–gold loading was significantly increased
through the use of seeds during the citrate reduction reaction with a 43% increase
in gold loading from the original seeds to those seeded four times. The resulting
nanocomposite material retains the properties of both individual components: (a)
magnetic Fe 2 O 3 properties and (b) plasmonic Au nanostructures.
Composite structures with plasmonic and magnetic properties provide unique
characteristics from bulk material including the localized surface plasmon bands
and ability for magnetic manipulation to allow the recyclability of the nanoparticle
structure for use in future reactions, reducing cost and use of precious metals such
as gold.