Functionalized core-shell Ag@TiO2 nanoparticles for enhanced Raman spectroscopy: A sensitive detection method for Cu(II) ions

Article abstract of DOI:10.1039/c8cp07504b

This paper demonstrates the use of surface plasmon resonance of core-shell Ag@TiO₂ particles in SHINERS experiments. A copper(ii) complex grafted onto Ag@TiO₂ surface was probed by Raman spectroscopy using resonance excitation profiles vs. Excitation wavelengths (514, 633 and 785 nm) to tune the Raman signals. Enhancement factors of the SHINERS assembly have been estimated and compared to the SERS effect of unmodified silver NPs colloidal dispersions. Finally, the grafting of the copper(ii) complex onto Ag@TiO₂ was advantageously compared to the grafting onto Ag@SiO₂ shell.

Full text of DOI:10.1039/c8cp07504b

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Functionalized core-shell Ag@TiO2 nanoparticles for enhanced
Raman spectroscopy : a sensitive detection method for Cu(II) ions
Florian Forato,a Somayeh Talebzadeh,b Nicolas Rousseau,c Jean-Yves Mevellec,c Bruno Bujoli,a D.
Received 00th January 20xx,
Accepted 00th January 20xx
Andrew Knight,b Clémence Quefféleca* and Bernard Humbertc*
DOI: 10.1039/x0xx00000x
This paper demonstrates the use of Surface Plasmon Resonance of core-shell Ag@TiO2 particles in SHINERS experiments. A
copper(II) complex grafted onto Ag@TiO2 surface was probed by Raman spectroscopy using resonance excitation profiles vs
excitation wavelengths (514, 633 and 785 nm) to tune the Raman signals. Enhancement factors of the SHINERS assembly
have been estimated and compared to the SERS effect of unmodified silver NPs colloidal dispersions. Finally, the grafting of
the copper(II) complex onto Ag@TiO2 was advantageously compared to the grafting onto Ag@SiO2 shell.
www.rsc.org/
Enhanced Raman Scattering (SERS) that can increase a Raman
signal measurement by 104 to 1010, and small molecules can be
detected with small NPs or aggregates. In 2010, Li et al.25
Introduction
The study of core-shell metal nanoparticles (NPs) is an emerging
field and has attracted attention especially in the field of
photocatalysis,1–3 and a wealth of synthetic strategies are
available for these materials.4 Principally, these synthetic
strategies fall into two main categories: (a) a one-step
preparation of core-shell nanoparticles involving simultaneous
growth of noble metal nanoparticles and metal oxide shells, and
(b) coating of previously prepared metal nanoparticles with a
shell of metal oxide. This second approach often leads to
improved monodispersity of the core-shell structures and is also
attractive for the formation of non-centrosymmetric
morphologies.5,6 Some examples of interesting shapes include
yolk-shell7 Janus,8 flower-like9 and eccentric10 and many of
these structures exhibit novel plasmonic properties. Metal
oxides usually employed are silicon oxide11–14 although titanium
or zirconium oxide have been employed as well.15 Regarding the
metals, gold, copper and silver have been the most used, and
silver has probably played the most important role in the
development of plasmonics.16
developed SHell-Isolated Nanoparticle-Enhanced Raman
spectroscopy (SHINERS) in which the Raman amplification of the
signal was provided by gold nanoparticles with an ultrathin silica
or alumina shell. This core-shell prevented the aggregation of
NPs without loss of the SPR effect. Since then, the SHINERS
technique has been extended to others metals, (also including
non-reactive shells) and has been employed for various
applications.26–30 In this work, the binding of phosphonic acid-
based organometallic complexes to core-shell Ag@TiO2
nanoparticles is described and is compared to the silicon oxide
shell analog. This paper demonstrates the importance of
controlling the TiO2 shell in SERS applications. Silver is known to
possess an intense plasmon band,24,31 and is a relatively
inexpensive metal. We decided to focus our attention towards
Ag@TiO2 NPs, in which the titania shell prevents oxidation of
silver and allows the grafting of a bipyridine-based ligand
bearing a phosphonic acid group through the formation of an
iono-covalent bond. The SPR of our SHINERS core-shell Ag@TiO2
particles is used here to probe a copper(II) complex adsorbed
onto the surface by Raman spectroscopy using plots of
enhancement profiles vs excitation wavelengths. The best
SHINERS effect for the copper(II) complex is observed with a
low-focused power laser excitation at 633 nm, as the SHINERS
effect is much weaker for example at 785 nm and at 514 nm.
Specifically, for green excitation, the copper complex degraded
Surface Plasmon Resonance (SPR) is an interesting
characteristic of metal NPs which has been largely employed for
surface enhanced spectroscopy,17 biological and chemical
imaging,18,19 lithographic fabrication,20–22 and other
applications.16,23,24 One of the major developments is Surface
a.Chimie Et Interdisciplinarité: Synthèse Analyse Modélisation (CEISAM), Université
de Nantes, CNRS, UMR 6230, 2, rue de la Houssinière, BP 92208, 44322 Nantes
Cedex 3, France. E-mail : clemence.queffelec@univ-nantes.fr
b.Chemistry Department, Florida Institute of Technology, 150 West University
Boulevard, Melbourne, Florida, 32901, USA
after only
a few seconds. This paper also compares
enhancement factors of the SHINERS assembly with the SERS
effect of unmodified silver NPs colloidal dispersions by using the
enhanced Raman spectrum of the bipyridine skeleton. Finally,
we demonstrate using the Raman signals, that the TiO2 shell
does not possess a direct chemical bonding interaction between
Ag atoms and the bipyridine ligand. As copper is an important
metal used in a wide variety of applications and its detection in
aqueous and organic solvents is of interest, we have
c. Institut des Matériaux Jean Rouxel, CNRS-Université de Nantes, 2 rue de la
Houssinière, B.P. 32229, 44322 Nantes Cedex 3, France. E-mail :
Bernard.Humbert@cnrs-imn.fr
Electronic Supplementary Information (ESI) available: [Synthesis of nanomaterials,
sample preparation for Raman, UV-vis spectra of Ag@SiO2 and Ag@SiO2@bpy-PA
and TEM images, Raman spectrum at 633 nm of Ag@TiO2@bpy-PA NPs at the
millimolar and the micromolar concentration]. See DOI: 10.1039/x0xx00000x
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120 keV, using holey carbon-coated copper grids (V3ie0w0AmrticelesOhn)litnoe
investigated the possibility of copper ion detection using SERS
by direct complexation with the N-N donor set of grafted
bipyridine groups on SHINERS particles.
gain enough electronic contrast.
DOI: 10.1039/C8CP07504B
UV-Vis absorption
UV-Vis absorption spectra were obtained on a 5000 CARY
VARIAN spectrophotometer using water, or dichloromethane as
the solvent for organic compounds.
Material and methods
Starting materials.
All chemical reagents and solvent were purchased from
commercial sources (Aldrich, Acros, SDS) and used as received.
1H NMR spectra were recorded on Bruker Avance 300 MHz or
400 MHz spectrometers. Chemical shifts are reported (in parts
per million) relative to internal tetramethylsilane (Me4Si, δ =
0.00 ppm) or referenced to the residual solvent. Silica gel (200-
300 mesh) was used for flash chromatography. TLC plates were
visualized by immersion in anisaldehyde or permanganate stain
followed by heating.
Comparison of the enhancement of Raman signals
In order to estimate the enhancement factor of our SHINERS
NPs and to test the lack of accessibility of bipyridine towards
binding at the silver interface, our spectra were compared with
SERS signals obtained with silver colloidal NPs in the presence
of an aqueous solution of bipyridine (10-4 M).34 The colloidal
dispersion of silver NPs was synthesized by the usual method in
aqueous medium by the reduction of AgNO3 by NaBH4. The
quasi spherical Ag NPs with a diameter around 14 nm ± 7 nm
was either deposited on a pure silica glass or used directly in
suspension in contact with 2,2'-bipyridine solutions. Colloidal
silver NPs were also functionalized by a self-assembly C12 spacer
thiol monolayer (SAM) in order to have a protective layer
between bipyridine molecules and silver NPs. Signal intensities
allowed us to estimate the magnitude of enhanced factors of
our shiners at the same wavelengths for the same quantity of
bipyridine groups adsorbed per square nanometer.
The syntheses of the ligand bpy-PA and Ag@TiO2@L@Cu NPs
have been reported previously.32
RAMAN spectroscopy
Raman spectra were recorded using a microconfocal Raman
inVia
 Reflex Renishaw device. The instrument was equipped
with a double edge filter to eliminate the Rayleigh scattering,
and a charged couple device (CCD) camera working at a
temperature of 220 K and with a 1024 by 256 pixel array. Laser
excitations used were 457.9, 488, 514.53, 632.82 and 785 nm
wavelengths. The setup was composed of
a confocal
microscope that was equipped with an automated XYZ table. Results and discussion
The spectral resolution achieved with the use of gratings of
2400, 1800 or 1200 grooves per millimetre was between 2 and
1. Synthesis of ligand bpy-PA
The 2,2’-bipyridine (bpy) ligand is ubiquitous in metal
3.5 cm-1 according to the excitation wavelength. All the Raman
characteristics (optical responses vs wavelength, vs
polarisation, wavenumber accuracy, stability etc.) were
calibrated based on previous methods.33 The accuracy of the
wavenumber, verified with the silicon Raman signal, was better
than 0.5 cm-1. The focused power of the laser beam was also
checked for each wavelength to avoid any transformation or
heating of the samples. Accordingly, the power was kept below
coordination chemistry and is able to coordinate to a large
number of transition metal ions in solution usually with high
binding constants. The wealth of different coordination
geometries that bipyridine (bpy) metal complexes may adopt
can give rise to different Raman spectral features. This has been
exploited recently in the use of the bpy ligand in combination
with Ag nanoparticles for the detection of a wide variety of
metal ions in aqueous solution including Fe(II), Zn(II), Cu(II),
Cd(II) and Cr(III). Rapid SERS analysis was achieved using a
benchtop Raman spectrometer fitted with a 96-well microtitre
plate.35
We focused on the ligand bpy-PA for which the synthesis has
previously been reported.32 Briefly, 4,4’-dimethyl-2,2’-
bipyridine was functionalized with one aldehyde group36,37 that
allowed attachment of the phosphonate tether bearing
oxyamine end-groups (NH2-O-(CH2)3-P(O)(OR)2) in ethanol, via
the formation of a stable O-alkyloxime bond (-C=N-O-). Then
hydrolysis of the phosphonate esters using McKenna’s
method38 afforded ligand bpy-PA in a good yield (Scheme 1,
19.2% over 5 steps).
100 µW/µm2 and the magnitudes
50 and x20 of the objective
(numerical aperture respectively of 0.75 and 0.35 and then a
spot size of around respectively of 1.5 and 15 µm2) has been
selected after a test list. The confocal mode was also sometimes
used to select a smaller analyzed volume in the same irradiated
volume and to record Raman spectra with the better lateral
spatial resolution (around at
/2) in order to check the
heterogeneity of our films. The acquisition time was between 1
s and 30 s in order to obtain an enough signal-to noise ratio
without damaging the samples.
For sample preparation, colloidal solutions were dropped onto
silica slides under a flow of argon gas until water evaporation,
approximately fifteen successive evaporations are needed in
order to obtain a suitable amount.
Nanoparticle characterization
Nanoparticle morphology was investigated by transmission
electron microscopy (TEM, 1230 Jeol) working at a voltage of
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is thus of interest. We first decided to look at copper(II) ions due
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to their high stability in water.
For the synthesis of Ag@TiO2@bpy-PA-Cu(II), an aqueous
copper(II) solution was added to Ag@TiO2@bpy-PA suspension.
(molar ratio Ag/Ti is around 0.06%).32 After 16 hours,
Ag@TiO2@bpy-PA-Cu(II) was obtained after centrifugation,
allowing the formation of spherical nanoparticles. Dynamic light
scattering (DLS) measurements were performed, but due to
evolutive aggregation, their interpretation and simulations
couldn’t be used with confidence. As such, we chose to perform
a statistical analysis of TEM images for the size determination of
silver NPs in the Ag@TiO2 nanocomposite.
Scheme 1. Synthesis of ligand bpy-PA
Figure 1 shows a TEM image of Ag@TiO2@bpy-PA-Cu(II) in
which spherical nanoparticles are shown with an average
diameter around 20 nm.
2. Synthesis of Ag@TiO2@bpy-PA and characterization
It is important to point out that a titanium oxide shell was
chosen over silicon oxide for two different reasons :
- We recently investigated the immobilization of a rhodium
complex based on phosphonate-functionalized 2,2’-bipyridine
on titanium oxide particles generated in situ. Successful
immobilization of the catalysts on titanium oxide particles was
demonstrated by different characterization techniques [31P
magic angle spinning (MAS) NMR spectroscopy correlated with
DFT calculations, X-ray photoelectron spectroscopy (XPS), and
time-of-flight secondary-ion mass spectrometry (ToF-SIMS)].39
We thus assumed the grafting would be similar in the case of
Ag@TiO2 and will ensure a strong binding between the ligand
and the core-shell NPs.
Figure 1. TEM images of a) Ag@TiO2@bpy-PA b) Ag@TiO2@bpy-
PA-Cu(II) NPs
4. UV-Vis absorption spectroscopy
- Silicon oxide shell usually leads to well-dispersed Ag@SiO2
core-shell NPs. We synthesized Ag@SiO2 NPs following an
adapted procedure from literature40,41 and monodispersed NPs
were obtained (Figure S1). Then the ligand was added to form
Ag@SiO2@bpy-PA NPs, and comparison of Ag@SiO2, before
and after grafting, demonstrated that the silica layer was
partially destroyed and a high degree of silver NP aggregation
appears to be present in the TEM images (Figure S2). We
currently do not have an explanation for this phenomenon.
However, for these reasons, Ag@TiO2 was selected over
Ag@SiO2 for the SHINERS experiments.
The synthesis of silver NPs is quite straightforward and Ag NPs
were obtained from the reduction of silver nitrate with
hydrazine monohydrate to give a yellow coloured solution of
stable Ag NPs and TiO2 core-shell was then formed through the
hydrolysis of titanium tetraisopropoxide (TTIP) in water.5,32 The
Ag NPs were randomly distributed in the titania matrix and
Ag@TiO2 nanocomposites had a silver core diameter ca. 10-30
nm and the TiO2 shell thickness was ca. 2-10 nm (Figure S3).
A bpy-PA solution in water was added to the Ag@TiO2 NPs and
left to stir overnight. The resulting Ag@TiO2@bpy-PA
nanocomposite was concentrated by cross-flow filtration,
centrifuged, washed exhaustively with water to remove any
unreacted phosphonic acid and redispersed in water.
The formation of colloids was monitored by UV-vis absorption
spectroscopy and a spectral comparison of unprotected Ag NPs,
core-shell Ag@TiO2, Ag@TiO2@bpy-PA and Ag@TiO2@bpy-PA-
Cu(II) are shown in Figure 2. The plasmon band can clearly be
seen in all four samples confirming the formation of
nanoparticles. The peak maximum corresponding to the
plasmon excitation of silver is around 405 nm.16 As expected
with the encapsulation and the change of surrounding
environment (dielectric shell around metal particles),42 the
plasmonic band is red-shifted to 445 nm and decrease in
intensity when coated with TiO2. When ligand bpy-PA is
attached to the Ag@TiO2 NPs, the plasmon resonance band is
further red-shifted to 450 nm. Upon coordination of metal ions
to Ag@TiO2@bpy-PA nanocomposites, the shape of the
transmission spectrum is nearly unchanged. For copper(II), the
spectrum displays a broadening of SPR band around 450 nm
related to the plasmon resonance and some copper-complex
electronic transitions can be observed in the near IR region.
3. Synthesis of Ag@TiO2@bpy-PA-Cu(II) and characterization
Copper is an important metal used in a wide variety of
applications and its detection in aqueous and organic solvents
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slides were dipped 5 min into the copper solutions, then dried
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DOI: 10.1039/C8CP07504B
before Raman characterization.
5.2. Raman data for Ag@TiO2@bpy-PA at 514 nm
To characterize the grafted complexes, Raman measurements
were first performed with a laser excitation at 488 nm.
Ag@TiO2@bpy-PA was the first sample studied and was
compared to a sample of the ligand grafted directly onto TiO2
particles (TiO2@bpy-PA). Mostly signals corresponding to the
bipyridine skeleton were observed in the presence of Ag NPs
and no signals were detected for TiO2@bpy-PA, even with a
laser power two hundred times higher. These results confirm
that silver nanoparticles are required to enhance the signals of
the ligand, suggesting as well that the amount of ligand bound
to the TiO2 surface is too low to be directly detected, on both
Figure 2: UV-vis spectra of Ag@TiO2@bpy-PA-Cu(II) NPs; Arrows
indicate the different excitation wavelength of Raman spectra,
514.53, 632.8 and 785 nm displayed in Figures 3 and 4.
concentrations tested. Moreover, after
a few seconds,
additional fluorescence signals were observed and the overall
spectrum changed, suggesting a degradation of the sample
under laser irradiation.
5. Enhanced Raman Spectroscopic Study
Therefore, the laser wavelength was changed to 514 nm. We
first looked at adsorbed bipyridine molecules on rough silver
electrodes (Figure 3A)42 or adsorbed bipyridine molecules with
a thiol tether on colloidal silver nanoparticles (Figure 3B). As
expected, the SERS effect of the bipyridine group is weaker with
an organic spacer than the enhancement obtained using
directly adsorbed bipyridine molecules on colloidal Ag NPs
(Figure 3A) but these are always observed. The Raman spectrum
of the Ag@TiO2@bpy-PA film was thus recorded at 514 nm at a
low focused laser power (ca. 100µW per 5 µm2) in 1 second
(Figure 3C) and then was compared to the two other samples
described above to qualitatively assign the vibrational Raman
scatterings.
5.1. Samples preparation for Raman spectroscopy
Backscattered Raman spectra of Ag@TiO2@bpy-PA and
Ag@TiO2@bpy-PA@Cu(II) nanocomposites were recorded on
films directly deposited from the colloidal solution onto pure
silica glass slides. The percentage of coverage by the bpy-PA
ligand onto core-shell NPs was tested during our Raman
analyses. We grafted (i) around 400 bpy-PA per nm2 (multilayer
of bpy-PA around NPs) while using a millimolar aqueous
solution of ligand or (ii) approximatively one bpy-PA/nm2
(submonolayer of bpy-PA on NPs) when using a micromolar
aqueous solution of ligand.
Raman spectra were recorded for both concentrations and for
the lowest concentration, the spectra were less noisy (Figure
S4). Therefore, only results with the micromolar concentration
are shown. It is important to point out that for detection, the
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Figure 3 : (A) Raman spectrum of 2,2’-bipyridine at 10-4 M in a colloidal solution of Ag at 514 nm. In the insert, zoom on the range
spectrum of 200 and 350 cm-1 showing a Ag-bpy band around 260 cm-1; (B) Raman spectrum of 2,2’-bipyridine with a thiol
functionalized C-12 spacer at 10-4 M in a colloidal solution of Ag at 514 nm (C) Raman spectrum of Ag@TiO2@bpy-PA (power
density : 25 µW.µm-2) at 514 nm. The quantity adsorbed of bpy-PA is around the monolayer at the surface of Ag@TiO2.
The spectrum of Ag@TiO2@bpy-PA is dominated by the 2,2’-bipyridine without SERS, and the EF would be between 5
vibrational modes of the bipyridine unit and is very similar to 107 and 108, which is consistent with data of literature).
that obtained using adsorbed bipyridine molecules with an
5.4. Raman results at 633 nm
organic thiol tether on colloidal Ag NPs (Figure 3B). By
comparing recorded intensities of signals and focused power
values at the same wavelength, the enhancement for
Ag@TiO2@bpy-PA may be estimated to be three orders of
magnitude weaker than for colloidal Ag@bpy NPs. The SERS
spectra display the active modes of bipyridine in five principal
ranges (i) 1600-1560 cm-1, modes involving C=C and C=N
stretchings and possible in-plane CNH deformations; (ii) 1500-
1450 cm-1 for C=C and C=N ring stretching and the CCH in-plane
deformations; (iii) 1250-1150 cm-1 for CCH in-plane
deformations weakly coupled with the ring stretching modes;
(iv) 1100-980 cm-1 for ring breathing modes and (v) 300-200 cm-
Because 514 nm is too high in energy resulting in some
degradation of the material, we then recorded the spectrum of
Ag@TiO2@bpy-PA at 633 nm and we compared it to
Ag@SiO2@bpy-PA (Figure S4). With a low power laser, the
spectrum of Ag@TiO2@bpy-PA displayed bipyridine modes
while for Ag@SiO2@bpy-PA, the spectrum is more complicated
and was evolving and degrading during acquisition. Some
spectral feature of bipyridine can be observed with other peaks
probably arising from the degradation of the bipyridine
backbone. Besides, during acquisition, the peak corresponding
to Ag-N bond could be observed around 250-260 cm-1,
confirming the result obtained by TEM.
1
for possible Ag-N modes (insert in Figure 3A). This last range
exhibits no signal for all Ag@TiO2@bpy-PA samples, thus no
bonds between the silver surface and bipyridine groups was
observed.
Then, we compared spectra of Ag@TiO2@bpy-PA and
Ag@TiO2@bpy-PA-Cu(II) (Figure 4). The signal at 230 cm-1
observed for Ag@TiO2@bpy-PA-Cu(II) is representative of the
Cu-N bond. As show in the Figure 4 inset, a small shift in the
wavenumber values for the bipyridine modes could be
5.3. Evaluation of the enhancement factor
The SERS enhancement factor of our core-shell Ag@TiO2@bpy- observed, confirming that copper is coordinated to the
PA NPs has been estimated in two different ways (for more bipyridine skeleton. In this case, we observed no Ag-N signals.
details, see the Supporting Information):
(i) This factor may be expressed as the ratio {I(sers intensity at
one wavenumber) per molecule / I(usual raman at the same
wavenumber) per molecule}, where both intensities are excited
with the same incident power focused on the same area and the
wavenumber corresponds to the characteristic Raman shift of
the molecule. As the Raman profile is different between the
conventional bipyridine fragments (not displayed here) and the
SERS bipyridine fragments of our sample, the same
wavenumber for both structures is not easy to choose. In our
case, the signals around 1010 and 1490 cm-1 (Figure 3, peaks
labels with stars) could be used for calculations. With the
integrated intensities, we can claim then that the enhancement
factor in our case is between 500 and 2x103.
(ii) The factor may be estimated also by comparing Raman
spectra obtained with our core-shell systems to the ones
recorded with colloidal silver NPs interacting with bipyridine
molecules. Profiles are in this case very similar and the Figure 4 : Black : Raman spectrum of Ag@TiO2@bpy-PA (power
enhancement factor may be evaluated by using different density : 75 µW.µm-2) at 633 nm. Blue : Raman spectrum of
signals. Thus, our system is 10-3 to 10-4 less efficient than Ag@TiO2@bpy-PA-Cu(II) (power density : 75 µW.µm-2) at 633
colloidal silver NPs and 10-2 to 10-3 less efficient than capped nm.
silver NPs by C12 long chains. (NB : with our calculation method,
5.5. Comparison of Raman results at different wavelengths for
Ag@TiO2@bpy-PA-Cu(II)
we could estimate the enhancement factor per bipyridine
adsorbed on colloidal silver NPs by comparing their responses
to the conventional Raman recorded with our device for the
Finally, spectra of Ag@TiO2@bpy-PA-Cu(II) were compared at
three different wavelengths, 514, 633 and 785 nm (Figure 5).
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Figure 5: Comparison of Raman spectrum of Ag@TiO2@bpy-PA-Cu(II). In green at 514 nm (power density : 50 µW.µm-2), in red at
633 nm (power density : 75 µW.µm-2) and in black at 785 nm (power density : 175 µW.µm-2).
selectively copper ions in aqueous solutions at the picomolar
At 633 and 785 nm, the Cu-N bond can be well observed. It is level. The method might be straightforward, robust and
important to point out that at 785 nm, luminescence of silica applicable in harsh environments such as sea-water where the
originating from the glass slide caused interference with the simple SERS method may be limiting. The ability of the sensor
samples between 1200 and 1800 cm-1 and it was clearly difficult platform to be recycled and to selectively detect other metal
to observe the bipyridine signals. At 514 nm, the sample was ions will be included in future work.
degrading after a few seconds. Thus, it seems from these results
that 633 nm is the best compromise for the signal enhancement
and sample stability.
Conflicts of interest
There are no conflicts to declare.
Conclusion
Acknowledgements
In conclusion, we have developed a new SERS platform by using
shell-isolated NPs capped by titanium oxide and functionalized
by 2,2’-bipyridine bearing a phosphonic acid end-group. We
demonstrated here that a titanium oxide (TiO2) shell is able to
minimize the problem encountered with an analogous silicon
oxide shell and a phosphonic acid group. The SERS effect is
demonstrated with an enhancement factor of 103-104, i.e. 10-3
to 10-4 lower than the SERS signal obtained with an uncoated
silver NP. Moreover, Shell Isolated Enhanced Raman
Spectroscopy (SHINERS) was demonstrated for the copper(II)
coordination complex. The efficiency was optimum with a 633
nm excitation. On this basis, this new platform will be
investigated as a potential new analytical technique to detect
The authors acknowledge financial support from the “Centre
National de la Recherche Scientifique” (CNRS) through the PICS
COSMOCAT.
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TOC
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shell-isolated nanoparticle enhanced surface Raman
technique for detection of copper(II)
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