Modified glassy carbon electrode with AuNPs using cis-[RuCl(dppb)(bipy)(4- vpy)]+ as crossed linking agent

Article abstract of DOI:10.1016/j.poly.2014.04.024

This work links aspects of non-covalent interaction among gold nanoparticles (AuNPs) and ruthenium complexes, which were used to modify the surface of the glassy carbon electrode (GCE), without the necessity of a sulfur substrate with a covalent bond between gold-sulfur (Au-S), to keep the AuNPs onto the surface of the electrode. The AuNPs were synthesized by the method of encapsulation by citrate conferring on them a negative charge. The ruthenium complex [RuCl(dppb)(bipy)(4-vpy]⁺ was synthesized by ligand exchange in its coordination sphere, giving it a positive charge. A thin film of [RuCl(dppb)(bipy)(4-vpy)]⁺ was generated onto the surface of glassy carbon electrode (GCE), using cyclic voltammetry, under potential cycling between -0.9 and -2.4 V, to produce the CGE-Ru⁺ electrode. Afterward, the GCE-Ru⁺ electrode was kept in a colloidal suspension of AuNPs for 1 h to incorporate them onto the surface of GCE-Ru⁺ by electrostatic interaction. The resulting electrode GCE-Ru-AuNPs was finally washed with water to remove the excess of AuNPs and it was used to acetaminophen detection by cyclic voltammetry. To find the optimum analysis conditions of the modified electrode, studies were conducted to understand; which were: the number of cyclic voltammograms to produce the film, dip-coating time in AuNPs, pH, scan rate and repeatability. The Ru-AuNPs aggregates were analyzed by UV-Vis spectroscopy (UV-Vis), Fourier transform infrared spectroscopy-attenuated total reflectance (FTIR-ATR), nuclear magnetic resonance of phosphorus ( ³¹P{¹H} NMR), cyclic voltammetry (CV); scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS) and transmission electron microscopy with energy dispersive spectroscopy (TEM-EDS). The X-ray structure of [RuCl(dppb)(5,5′-Me-bipy)(4-vpy)](PF₆) was determinate.

Full text of DOI:10.1016/j.poly.2014.04.024

Polyhedron 78 (2014) 46–53
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Modified glassy carbon electrode with AuNPs using
cis-[RuCl(dppb)(bipy)(4-vpy)]+ as crossed linking agent
Vanessa F. Ferreira a,1, Cássio R.A. Do Prado a, Carolina M. Rodrigues a, Larissa Otubo b, Alzir A. Batista c,
José W. da Cruz Jr. c, Javier Ellena d, Luís R. Dinelli a, André L. Bogado a,
⇑
a Faculdade de Ciências Integradas do Pontal, Universidade Federal de Uberlândia, Rua vinte, 1600, CEP 38304-402 Ituiutaba, MG, Brazil
b Centro de Ciência e Tecnologia de Materiais, Instituto de Pesquisas Energéticas e Nucleares, Av. Prof. Lineu Prestes 2242, Cidade Universitária, CEP 05508-000 São Paulo, SP, Brazil
c Departamento de Química, Universidade Federal de São Carlos, CP 676, CEP 13565-905 São Carlos, SP, Brazil
d Instituto de Física de São Carlos, Universidade de São Paulo, CP 780, 13560-970 São Carlos, SP, Brazil
a r t i c l e i n f o
a b s t r a c t
Article history:
This work links aspects of non-covalent interaction among gold nanoparticles (AuNPs) and ruthenium
complexes, which were used to modify the surface of the glassy carbon electrode (GCE), without the
necessity of a sulfur substrate with a covalent bond between gold–sulfur (Au–S), to keep the AuNPs onto
the surface of the electrode. The AuNPs were synthesized by the method of encapsulation by citrate con-
ferring on them a negative charge. The ruthenium complex [RuCl(dppb)(bipy)(4-vpy]+ was synthesized
by ligand exchange in its coordination sphere, giving it a positive charge. A thin film of [RuCl(dppb)
(bipy)(4-vpy)]+ was generated onto the surface of glassy carbon electrode (GCE), using cyclic voltamme-
try, under potential cycling between ꢀ0.9 and ꢀ2.4 V, to produce the CGE–Ru+ electrode. Afterward, the
GCE–Ru+ electrode was kept in a colloidal suspension of AuNPs for 1 h to incorporate them onto the sur-
face of GCE–Ru+ by electrostatic interaction. The resulting electrode GCE–Ru–AuNPs was finally washed
with water to remove the excess of AuNPs and it was used to acetaminophen detection by cyclic voltam-
metry. To find the optimum analysis conditions of the modified electrode, studies were conducted to
understand; which were: the number of cyclic voltammograms to produce the film, dip-coating time
in AuNPs, pH, scan rate and repeatability. The Ru–AuNPs aggregates were analyzed by UV–Vis spectros-
copy (UV–Vis), Fourier transform infrared spectroscopy–attenuated total reflectance (FTIR–ATR), nuclear
magnetic resonance of phosphorus (31P{1H} NMR), cyclic voltammetry (CV); scanning electron micros-
copy with energy dispersive spectroscopy (SEM–EDS) and transmission electron microscopy with energy
dispersive spectroscopy (TEM–EDS). The X-ray structure of [RuCl(dppb)(5,50-Me-bipy)(4-vpy)](PF6) was
determinate.
Received 21 February 2014
Accepted 15 April 2014
Available online 23 April 2014
Keywords:
Gold nanoparticles
Ruthenium complexes
Electrostatic interaction
Modified glassy carbon electrode
Acetaminophen detection
Ó 2014 Elsevier Ltd. All rights reserved.
1. Introduction
nucleation and successive growth. When the nucleation and suc-
cessive growth are completed in the same process, it is called
More than 70000 publications have appeared on gold nanopar-
ticles (AuNPs) to date, which have been producing recent develop-
ments in the synthesis and functionalization of AuNPs [1,2]. AuNPs
can be prepared by both ‘‘top down’’ and ‘‘bottom up’’ approaches,
where the control of size and shape of particles, as well as further
functionalization is more effortlessly obtained in bottom up
method, by chemical or biological reduction of individual
molecules. This chemical reduction method involves two steps:
in situ synthesis; otherwise it is called seed-growth method [1].
In this context, the ‘‘in situ’’ Turkevich–Frens [3,4] method, to
obtain ca. 10 to 150 nm AuNPs, and the Brust–Schiffrin [5,6]
method, to obtain hydrophobic AuNPs with diameters in 1 to ca.
8 nm ranges are still major synthetic routes [2].
Stabilization and functionalization of AuNPs has been exten-
sively reviewed in AuNPs obtained from both, in situ or seed-growth
method. Three kids of widely used methods to functionalization of
AuNPs are: electrostatic interaction, specific recognition and cova-
lent coupling [2].
⇑
Corresponding author. Address: Rua vinte, 1600, Bairro Tupã, CEP 38.304-402
Ituiutaba, MG, Brazil. Tel.: +55 (34) 3271 5251; fax: +55 3271 5246.
AuNPs and functionalized AuNPs have been used for a wide
range of application in many fields of knowledge. Only for illustra-
tion they are applied at: chemiluminescence sensors [7]; catalysis
E-mail address: albogado@pontal.ufu.br (A.L. Bogado).
Present address: Instituto de Química de São Carlos, Universidade de São Paulo,
1
CP 780, 13560-970 São Carlos, SP, Brazil.
http://dx.doi.org/10.1016/j.poly.2014.04.024
0277-5387/Ó 2014 Elsevier Ltd. All rights reserved.

V.F. Ferreira et al. / Polyhedron 78 (2014) 46–53
47
in liquid phase [8–9]; hybrid nanobiomaterials [9–11]; biodiagnos-
tics [12] and plasmonic sensors [13].
5 mm inverse probe head. Samples for 31P{1H} experiments were
prepared under on inert atmosphere and measured at room tem-
perature, with methylene chloride (CH2Cl2) as solvent and a D2O
capillary. Chemical shifts were reported with respect to the phos-
phorus signal in 85% phosphoric acid (H3PO4).
The microanalyses were performed at Universidade Federal de
São Carlos, São Carlos (SP), using a FISONS CHNS-O, mod. EA
1108 Element analyzer.
Most of the techniques reported for immobilizing ligands to
AuNPs surfaces are based on Au–S covalent bond formation
between the ligands and the gold atoms on the particle surfaces.
This approach necessitates the use of sulfur containing ligand,
i.e., thiol, disulfide and thiolester [9–11]. Nanoparticles functional-
ized with groups that provide affinity sites for the binding of bio-
molecules have also been used for the specific attachment of
proteins and oligonucleotides [2]. Electrostatic interaction, non-
covalent interaction or physical adsorption immobilization of spec-
imen for AuNPs probes are simple processes with the benefits of
time saving and reduced complexity of ligand preparation. Its rel-
ative simplicity gives this approach certain advantages over the
complex covalent immobilization or specific recognition methods.
Non-covalent interactions are considerably weaker than covalent
interactions, which can range between ca. 150 to 450 kJ molꢀ1 for sin-
gle bonds. The term ‘‘non-covalent’’ includes a wide range of attrac-
tions and repulsions, which consist of ion–ion (200–300 kJ molꢀ1),
ion-dipole (50–200 kJ molꢀ1), dipole–dipole (5–50 kJmolꢀ1), hydro-
Optical spectra were recorded on a Perkin Elmer model lambda
25 spectrophotometer with 1 cm quartz cell between 300 and
800 nm and FTIR spectra were recorded in an ATR apparatus with
diamond cell support or conventional KBr cell of 0.2 mm length
with a Jasco FTIR 4000 spectrometer in the 4000–400 cmꢀ1 range.
Electrochemical data were obtained using a potentiostat/galva-
nostat l )
-autolab type III. Solutions of the complexes (10ꢀ3 mol Lꢀ1
were prepared in dichloromethane (CH2Cl2) using 10ꢀ3 mol Lꢀ1
tetrabutylammonium hexafluorophosphate (TBAH) as the support-
ing electrolyte. Measurements were made with a three-electrode
configuration cell. A platinum foil was used as the working and
auxiliary electrodes and Ag/AgCl, 0.10 mol Lꢀ1 TBAH in CH2Cl2 as
the reference electrode. Under the conditions used, E0 for the
gen bonding (4–120 kJ molꢀ1), cation-
p p–p
(5–80 kJ molꢀ1),
(0–50 kJ molꢀ1), van der Waals (<5 kJ molꢀ1) and hydrophobic inter-
action related to solvent–solvent interaction energy [14].
one-electron oxidation of [Fe(g
5-C5H5)2], added to the test solu-
tions as an internal calibrant, is +0.43 V.
The strongest non-covalent interaction, ion–ion and ion–dipole
interaction have been used to produce modified electrodes by elec-
trostatic interaction of anionic surface of AuNPs and cationic spe-
Field emission scanning electron microscopy (FE-SEM) images
and energy-dispersive spectroscopy (EDS) analysis were obtained
using a JEOL JSM 6701F coupled with an EDS detector. The sample
powder was directly dispersed on a SEM sample-holder using a
conductive carbon paint. Transmission electron microscopy
(TEM) images were obtained using a JEOL JEM 2100 (200 kV)
equipped with a scanning TEM unit (STEM) and an EDS detector.
The TEM sample were dispersed in isopropanol and dropped on a
400 mesh copper grid coated with a collodion film.
cies. Wang and coworkers [15,16] describes
a method for
effective immobilizations of cationic ruthenium complexes on an
electrode surface. Willner and co-workers [17,18] reported the
construction, via electrostatic cross-linking, an electroactive multi-
layer electrode by simultaneously depositing anionic AuNPs and
oligocationic cyclophanes. In both cases a donor S compound was
used to cross-link the AuNPs with a derived indium tin oxide
(ITO) electrode surface.
2.3. X-ray diffraction data
Recently our group described an electroactive carbon paste mod-
ified electrode, constructed by electrostaticinteraction ofAuNPs and
a cationic complex of ruthenium, without S donor compounds [19].
Importantly, the produced nanocomposites did not include thiol-
containing compounds, which could potentially decrease the cata-
lytic activity of ruthenium in electrochemical reactions. Herein is
described a new strategic route to incorporate AuNPs onto the sur-
face of a glassy carbon electrode (GCE), using the [RuCl(dppb)
(bipy)(4-vpy]+ as cross link agent between GCE and AuNPs.
Crystals of [RuCl(dppb)(5,50-Me-2,20-bipy)(4-vpy)]PF6 (3) were
grown by slow evaporation of a dichloromethane/diethyl ether
solution. The crystals were mounted on an Enraf-Nonius Kappa-
CCD diffractometer with graphite-monochromated Mo Ka
(l = 0.71073 Å) radiation. The final unit-cell parameters were based
on all reflections. Data were collected with the COLLECT program;
[25] integration and scaling of the reflections were performed with
the HKL DENZO-SCALEPACK software package [26]. Absorption
correction was carried out by the Gaussian method [27]. The struc-
ture was determined by direct methods with SHELXS-97 [28]. The
model was refined by full-matrix least squares on F2 by means of
SHELXL-97 [29]. All hydrogen atoms were stereochemically posi-
tioned and refined with a riding model. The ORTEP view shown
in Fig. 2 was prepared with ORTEP-3 for Windows [30]. Hydrogen
atoms on the aromatic rings were refined isotropically, each one
with a thermal parameter 20% greater than the equivalent isotropic
displacement parameter of the atom to which it was bonded. The
data collection and experimental details are summarized in Table 1,
and the selected bond distances and angles are given in the caption
of Fig. 2.
2. Experimental
2.1. Reagents
All reactions were carried out under an argon atmosphere
using standard Schlenk techniques. RuCl3ꢁxH2O, H[AuCl4], triphen-
ylphosphine (PPh3), 1,4-bis(diphenylphosphino)butane (dppb), 2,
20-bipyridine (bipy), 5,50-dimethyl-2,20-bipyridine (5,50-Me-bipy),
pyridine (py), 4-vinylpyridine (4-vpy), and sodium citrate were
purchased from Aldrich and used as received. Reagent grade sol-
vents were distilled prior to use. The [RuCl(dppb)(bipy)(py)](PF6)
(1) and [RuCl(dppb)(bipy)(4-vpy)](PF6) (2) were prepared as
described previously [20–24]. Herein we will be discussing only
unpublished results about these complexes. The cis designation
used here is related to the position of the bidentate ligands.
2.4. Synthesis of [RuCl(dppb)(5,50-Me-bipy)(4-vpy)](PF6) (3)
The cis-[RuCl2(dppb)(5,50-Me-bipy)] was prepared according to
literature methods [31,32]. Excess of 5,50-Me-bipy (0.160 g;
0.87 mmol) was added to
a dark-green solution (0.500 g;
2.2. Instrumentation
0.58 mmol) of [RuCl2(dppb)PPh3] [33], in 100 mL of CH2Cl2. The
solution was refluxed for 48 h under Ar and the resulting red solu-
tion was then reduced to 1–2 mL, and Et2O was added to precipi-
tate the product, which was collected by vacuum filtration,
washed with hexane (3 ꢂ 5 mL), Et2O (6 ꢂ 5 mL), and dried under
The NMR spectra of the compounds were performed at Univer-
sidade Federal de São Carlos, São Carlos (SP). They were acquired
with a Bruker DRX-400 spectrometer (9.4 T) equipped with a

48
V.F. Ferreira et al. / Polyhedron 78 (2014) 46–53
Table 1
gation, washed three times with water, and then dried under
vacuum.
summarizes crystal data and provides data collection and refinement parameters.
Empirical formula
[RuC47H47ClN3P2] PF6
Formula weight
T (K)
997.31
293(2)
2.7. Preparation of modifier electrode
Wavelength (Å)
Crystal system
Space group
Unit cell dimensions
a (Å)
0.71073
orthorhombic
Pbca
The [RuCl(dppb)(bipy)(4-vpy)]+ was linked on the surface of the
glassy carbon electrode (GCE) by adsorption and reduction of 4-
vinylpirydine group, which produced the glassy carbon–Ru+ elec-
trode (GCE–Ru+). It was used a conventional cell containing a single
compartment, a working GCE (2 mm Ø), a Pt counter electrode, and
an Ag/AgCl electrode as reference. Ten voltammograms were car-
ried out between ꢀ2.4 and 2.0 V with scan rate of 100 mV sꢀ1 of
14.669(3)
20.499(3)
29.401(6)
8841(3)
b (Å)
c (Å)
V (Å3)
Z
8
Dcalc (Mg/m3)
Absorption coefficient (mmꢀ1
F(000)
1.499
0.587
4080
a solution of [RuCl(dppb)(bipy)(4-vpy)](PF6) (6,0 mg; 6.2 lmol)
and TBAH (0.1 mol Lꢀ1) in dichloromethane (10 mL). The GCE–
Ru+ electrode was introduced in a colloidal suspension of citrate-
stabilized gold nanoparticles, with average diameter of about
14 nm (AuNPsꢀ, 0.05 mmol Lꢀ1 containing 9.9 mg of Au) within
60 min at room temperature. The characteristic interaction of
GCE–Ru+ and AuNPsꢀ has produced a bimetallic modified electrode
(GC–Ru–AuNPs), which was used to acetaminophen detection.
The GCE–Ru+ can be also prepared with in situ generation of
[RuCl(dppb)(bipy)(4-vpy)]+ from cis-[RuCl2(dppb)(bipy)] in the
presence of excess of 4-vinypiridine (5 eq. related to ruthenium
precursor), using the same configuration in the electrochemical
cell. The chlorine ligand exchange by 4-vinypiridine has formed
the same cationic complex containing ruthenium, which was
linked on the surface of GCE.
)
Crystal size (mm)
Reflections collected
Independent reflections (Rint
Completeness to h = 26.02°
Absorption correction
0.16 ꢂ 0.07 ꢂ 0.05
46980
)
8675 (0.0969)
99.7%
Gaussian
R1 = 0.0473, wR2 = 0.0986
R1 = 0.1074, wR2 = 0.1177
Final R indices [I > 2
r
(I)]
R indices (all data)
vacuum. Yield: 0.44 g (86%). Anal. Calc. for C40H40ClN2P2Ru: C,
61.38; H, 5.15; N, 3.58. Found. C, 61.24; H, 5.22; N, 3.68%.
31P{1H} NMR (162 MHz, CH2Cl2/D2O) d(ppm) 45.4 (d) and 31.8
2
(d) (d = doublets, Jp–p = 32.7 Hz).
The cis-[RuCl2(dppb)(5,50-Me-bipy)] (0.050 g; 0.057 mmol) was
dissolved in 20 mL of CH2Cl2 and 0.043 mL (0.400 mmol) of 4-
vinylpyridine was added to the red solution. Also, 0.022 g
(0.114 mmol) of KPF6 dissolved in 1.0 mL of methanol was added
to the same solution. The mixture was stirred for 24 h, at room
temperature, and then reduced to 1–2 mL, and Et2O was added
to precipitate the product, which was collected by vacuum filtra-
tion, washed with H2O (4 ꢂ 5 mL), and Et2O (5 ꢂ 5 mL), and dried
under vacuum. Yield: 0.51 g (92.5%). Anal. Calc. for C46H47ClN3P3F6
Ru: C, 56.07; H, 4.81; N, 4.26. Found. C, 55.31; H, 4.80; N, 4.54%.
31P{1H} NMR (162 MHz, CH2Cl2/D2O) d(ppm) 37.13 (d) and 36.16
3. Results and discussion
3.1. Syntheses and non-covalent interaction between AuNPs and
ruthenium complexes (Ru–AuNPs)
The [RuCl(dppb)(bipy)(4-vpy)](PF6) was prepared by ligand
exchange from cis-[RuCl2(dppb)(bipy) as ascribed by Batista and
co-workers [20]. Experimental and theoretical study of the kinetics
of dissociation in the cis-[RuCl2(dppb)(bipy)] revealed that only the
chloride trans to the phosphorus atom of the dppb ligand was dis-
sociated, even in the presence of excess of monodentate ligand,
such as monopyridine and functionalized monopyridine (Fig. 1).
Presence of more bulky group bonded in the N–N donor group,
such as 5,50-dimethyl-2,20-bipyridine (5,50-Me-bipy) produces the
cis-[RuCl2(dppb)(5,50-Me-bipy)], and it also lost the chloride coor-
dinated trans to P atom of dppb to produce a cationic complex con-
taining ruthenium in the presence of 4-vpy. Suitable crystals of
[RuCl(dppb)(5,50-Me-bipy)(4-vpy)](PF6) were obtained by slow
evaporation of a dichoromethane/diethyl ether solution. The data
collection and experimental details are summarized in Table 1
(Section 2), and selected bond distances and angles are given in
the caption of Fig. 2.
2
(d) (d = doublets, Jp–p 34.83 Hz). The complex presents a quasi-
reversible cyclic voltammogram in CH2Cl2, 10ꢀ3 mol Lꢀ1 Ru,
0.1 mol Lꢀ1 TBAP, scan rate 100 mV sꢀ1, at room temperature, with
Eox = 1200 mV and E1/2 = 1125 mV, close to those found for similar
chlorine complexes containing dppb, diimines and N-heterocyclic
as ligands [20,21,32,34–38].
2.5. Preparation of gold nanoparticles (AuNPs)
AuNPs with a diameter of 10–18 nm were prepared by citrate
reduction of H[AuCl4] in aqueous solution according to a well-
known method described by Frens [3]. In brief, 20 lL of solution
containing H[AuCl]4 (Au 58%) was added in 100 mL of water. The
resulting solution was brought to reflux, and 3 mL of sodium cit-
rate solution (1%) was introduced while stirring. The solution
was then kept boiling for another 30 min, while the colors change
from yellow to deep blue to red. Finally, the solution was left to
cool to room temperature.
The X-ray structural analysis of the complex [RuCl(dppb)(5,50-
Me-bipy)(4-vpy)](PF6) shows that the chloride is trans to one of
the 2,20-bipyridine nitrogens (N2) and the 4-vinylpyridine is trans
to one of the phosphorus atoms (P1). The Ru–N(1) (2.213 (3) Å)
distance is longer than the Ru–N(2) bond (2.067 (3) Å), as expected,
since the 4-vinylpyridine is a monodentate ligand, while the 2,20-
bipyridine is bidentate. In this case, the bidentate ligand is more
tightly bonded to the metal center. On the other hand, the distance
Ru–P(2) (2.3436 (10) Å), Ru–P(2) trans to N(3), is longer than the
distance Ru–P(1) (2.3186 (11) Å), Ru–P(1) trans to N(1), since the
2,20-bipyridine affects the P–Ru bonds trans to it more effectively
than does the monodentate 4-vinylpyridine ligand. The bond dis-
tances and angles listed in the caption of the Fig. 2 are in the range
expected for ruthenium biphosphine complexes [22,24,35–42].
Similar behavior was observed for the complexes containing
2.6. Aggregates of gold nanoparticles with ruthenium complexes
A
typical experiment using [RuCl(dppb)(bipy)(py)](PF6) is
described: (71.1 mg; 75.1 mol) of cationic ruthenium complex
l
was dissolved in acetone (10 mL) under magnetic stirring at room
temperature. After complete dissolution, it was transferred to a
stock solution of AuNPs in water (100 mL, 0.5 mmol Lꢀ1), which
was previously synthesized. Therefore, the formation of
quantitative brown precipitate occurred. It was collect by centrifu-
a

V.F. Ferreira et al. / Polyhedron 78 (2014) 46–53
49
Fig. 1. General structures of complexes studied in this work as PF6 salts.
Fig. 2. ORTEP view and atomic numbering of [RuCl(dppb)(5,50-Me-bipy)(4-vpy)](PF6) showing the atoms labeling and 50% probability ellipsoids. Bond lengths (Å): Ru–N2
2.067 (3), Ru–N3 2.119 (3), Ru–N1 2.213 (3), Ru–P1 2.3186 (11), Ru–P2 2.3436 (10), Ru–Cl 2.4315 (9). Bond angles (°): N2–Ru–N3 77.54 (11), N2–Ru–N1 84.87 (11), N3–Ru–
N1 83.13 (11), N2–Ru–P1 99.88 (8), N3–Ru–P1 89.91 (8), N1–Ru–P1 170.57 (8), N2–Ru–P2 101.80 (8), N3–Ru–P2 176.78 (8), N1–Ru–P2 93.67 (8), P1–Ru–P2 93.31 (4), N2–
Ru–Cl 168.81 (8), N3–Ru–Cl 92.69 (8), N1–Ru–Cl 88.59 (8), P1–Ru–Cl 85.38 (3), P2–Ru–cl 87.65 (3).

50
V.F. Ferreira et al. / Polyhedron 78 (2014) 46–53
4-methylpyridine and 4-phenylpyridine, as previously reported
[33,39,43,44]. In all three complexes, the dissociated chloride
was always the one trans to a phosphorus atom in the precursor
cis-[RuCl2(P-P)(bipy)] or cis-[RuCl2(P-P)(5,50-Me-bipy)] {where P-
P = aromatic biphosphine}, as expected, given the stronger trans
effect of the phosphorus atom and in accordance with the X-ray
structures.
In order to apply these kinds of complexes as cross-link agents
between glassy carbon electrode and AuNPs, the [RuCl(dppb)
(bipy)(4-vpy)](PF6) was prepared as previously described in the lit-
erature [20]. Cyclic voltammetry of [RuCl(dppb)(bipy)(4-vpy)](PF6)
has shown an oxidation potential (Eox) at 1.19 V and a reduction
potential (Ered) at 1.06 V due the redox pair RuIII/RuII, with half
coupling of plasmon absorbance of the particles [46,47]. Additional
amounts of [RuCl(dppb)(bipy)(4-vpy)]+ decrease the plasmon band
even more, until the metal-ligand charge transfer (MLCT) of the
ruthenium complex arises at 410 nm.
Aggregates of gold nanoparticles with ruthenium complexes
can be obtained as a powder (Ru–AuNPs) after addition of excess
of the cationic ruthenium complex into colloidal suspension of
AuNPs. A formation of a quantitative precipitate occurs, and it
can be collected by centrifugation and dried under vacuum.
The morphological and compositional analysis by electron
microscopy was realized with [RuCl(dppb)(bipy)(py)]+ and AuNPs-,
which produces a brown precipitate labeled as Rupy–AuNPs, as a
result of the electrostatic interactions. The Rupy–AuNPs were
investigated by SEM and TEM microscopy, both coupled to EDS
detectors, as present in the Figs. 4 and 5.
wave potential (E ) at 1.10 V. It also suggests a exchange between
½
chlorine (p-donor group) and 4-vpy (p-acceptor group) in the cis-
[RuCl2(dppb)(bipy)], producing a cationic ruthenium complex,
with increasing of potentials. The cis-[RuCl2(dppb)(bipy)] has vol-
tammetric parameters much more cathodic than the [RuCl(dppb)
SEM images of the resulting precipitate Rupy–AuNPs (Fig. 4A)
reveals that precipitate is an assembly of AuNPs and the ruthenium
complex, observed as round-shaped bright spots. These results are
accordingly to our previous observations published [19]. The chem-
ical composition of the precipitate was determined by the energy
dispersed spectroscopy (EDS), as shown in Fig. 4B. The peaks of Ru,
Cl, C, N, P and Au elements are observed (other peaks originated from
the substrate). This suggests that the precipitated formed consists in
a self-assembly of ruthenium cationic specimen and AuNPsꢀ.
Due the hydrophobic characteristic of the complexes containing
ruthenium aggregates onto the surface of AuNPsꢀ, the Rupy–AuN-
Ps are insoluble in water. Afterward the Rupy–AuNPs were dis-
persed in isopropanol and analyzed by TEM. The TEM images in
the Fig. 5A shown that the Rupy–AuNPs were partially dissolved
in isopropanol, leaving the AuNPs with average diameter about
20 nm (darker particles) and irregular shaped particles of ruthe-
nium complex. With higher magnification (Fig. 5A below) it is pos-
sible to observe the coalescence of some AuNPs. This result
suggests that the interactions between the cationic ruthenium
complex and AuNPsꢀ are non-covalent, and Rupy–AuNPs are act-
ing as a salt. AuNPs do not change the structure and the electronic
stability in solution of the applied ruthenium complex, because the
31P{1H} NMR and cyclic voltammetry data are the same in the
(bipy)(4-vpy)](PF6) {Eox = 0.64 V, Ered = 0.567 and E = 0.54 V} [45].
½
Infrared data of [RuCl(dppb)(bipy)(4-vpy)](PF6) revealed the
characteristics bands of their ligands, dppb, bipy and 4-vpy. These
aromatic ligands show a stretch at the 1435–1904 cmꢀ1 range,
which represents the C@C bonds, and the counter ion (PF6) show
a strong band at 853 cmꢀ1, due the P–F stretching.
Recently, we and others have been demonstrating the non-
covalent interaction between AuNPs and cationic specimen [16–
19] with different application in many fields of knowledge. The
process of interaction between cationic ruthenium complexes
Ru+ and the negative surface of gold nanoparticles (AuNPsꢀ) can
be accompanied by optical measurements [19].
Fig. 3 shows the plasmon band absorption of AuNPs (with aver-
age diameter of about 14 nm) at 520 nm [19]. After addition of
[RuCl(dppb)(bipy)(4-vpy)]+ (4 ꢂ 10ꢀ4 mol Lꢀ1 in acetone) to the
colloidal suspension of AuNPs (0.05 mol Lꢀ1), it was observed an
enlarged band, centralized at 629 nm, with significant decrease
of the original plasmon band of AuNPsꢀ at 520 mn. The polariza-
tion of the conduction electron oscillations in adjacent AuNPs
causes a red-shift on the plasmon absorbance, attributed to the
Fig. 3. Interaction of AuNPs and [RuCl(dppb)(bipy)(4-vpy)]+ accompanied by UV–Vis. (dashed line) colloidal suspension of AuNPs (0.05 mol Lꢀ1). (solid line) after addition of
600
l
L of [RuCl(dppb)(bipy)(4-vpy)]+ 4 ꢂ 10ꢀ4 mol Lꢀ1 in acetone.

V.F. Ferreira et al. / Polyhedron 78 (2014) 46–53
51
Fig. 4. (A) SEM image and (B) corresponding EDS spectrum of the resulting precipitate Rupy–AuNPs {Rupy = [RuCl(dppb)(bipy)(py)]+}.
Fig. 5. (A) TEM images of Rupy–AuNPs dissolved in isopropanol {Rupy = [RuCl(dppb)(bipy)(py)]+}. (B) TEM elemental maps related to Au, Ru, P and C elements.
presence and absence of AuNPs [19]. It is an important observation
to use the Ru–AuNPs species as a new material for further
application.
The Fig. 5B shows the elemental mappings obtained by EDS–
STEM mode of Rupy–AuNPs dispersed in isopropanol, with the dis-
tribution of Au, Ru, P and C in the STEM image. The Au mapping
confirms the AuNPs presence in the material as the spherical dark
spots. The slight shift observed on the elemental mappings is due
to a drift of the sample during scanning acquisition. Ru, P and C
are related to the ruthenium coordination complex and C is also
related to the citrated-capped AuNPs. The distribution mapping
also confirms the partial dissolution process of the solid in isopro-
panol. It is important to notice the P mapping, such as Ru mapping,
are very close to the AuNPs mapping, suggesting the permanence
of the ruthenium complex in the anionic species, after partially dis-
solution in isopropanol.

52
V.F. Ferreira et al. / Polyhedron 78 (2014) 46–53
3.2. Modified glassy carbon electrode with AuNPs using
[RuCl(dppb)(bipy)(4-vpy)]+ as crossed linking agent
A thin film of [RuCl(dppb)(bipy)(4-vpy)]+ was generated onto
the surface of glassy carbon electrode (GCE), using cyclic voltam-
metry, under potential cycling between ꢀ2.4 and +2.0 V, to pro-
duce the CGE–Ru+. An adsorption wave process of the 4-vpy
occurs at ꢀ1.2 V, and reduction waves processes at ꢀ1.6 and
ꢀ2.1 V. Similar potential related to adsorption and reduction pro-
cesses of vinyl group were observed by Franco and coworkers
[48] in the electropolymerization of trans-[RuCl2(4-vpy)4] on Au,
Pt and glassy carbon electrodes. Cyclic voltammetry of [RuCl2(4-
vpy)4] shows the vinyl reduction waves at the ꢀ1.5 and ꢀ2.45 V
range and adsorption wave around ꢀ0.8 V. Fig. 6 present the cyclic
voltammogram of [RuCl(dppb)(bipy)(4-vpy)]+, under potential
cycling between 2.0 and ꢀ2.4 V, in dichloromethane solution of
TBAH (0.1 mol Lꢀ1), using a working GCE, a Pt counter electrode,
and Ag/AgCl electrode as reference. Typical Ru (III/II), oxidation/
reduction wave are also observed at 1.16 and 1.05 respectively
Fig. 7. A) Cyclic voltammograms obtained with GCE–Ru–AuNPs in CH3COONa
solution (0.1 mol Lꢀ1) containing acetaminophen in different concentrations (99–
(E = 1.10 V), and vinyl reduction waves were observed in the
½
654
acetaminophen concentration (
l (lA) and
mol Lꢀ1). Scan rate of 100 mV sꢀ1. B) Linear relationship between Ipa
cathodic processes.
l
mol Lꢀ1).
After 10 voltammetry cycles the GCE–Ru+ electrode was
obtained and it was kept in a colloidal suspension of AuNPs for
1 h to incorporate them on the surface of GCE–Ru+ by electrostatic
interaction. The resulting electrode GCE–Ru–AuNPs was finally
washed with water and used for the detection of acetaminophen
by cyclic voltammetry.
0.083 lA l l
mol Lꢀ1 and 1.08 mol Lꢀ1. DL values were obtained as
follows: DL = 3sd/S, where sd = standard deviation of three blank
measures.
Ipa
ð
l
AÞ ¼ 2:062 þ 0:083Cð
l
molLꢀ1ÞðC in
l
molLꢀ1; R2 ¼ 0:999Þ
ð1Þ
3.3. Acetaminophen detection using CGE–Ru–AuNPs
The cyclic voltammogram response, using 0.01 mol Lꢀ1 of acet-
aminophen in GCE–Ru–AuNPs, was measured using different scan
rates over 50–550 mV sꢀ1 range. The Epa varied linearly with the
square root of the scan rate, indicating that the electrochemical
reaction is a diffusion-controlled process, as described by Eq. (2).
The anodic peak current (Ipa) response using GCE–Ru–AuNPs
electrode to acetaminophen detection increases with pH, reaching
a maximum at pH 5.5, and then decreases at alkaline pH. The ano-
dic peak potential (Epa) response is also dependent of pH condi-
tions, which indicates that the electrochemical reaction involves
a proton transfer. In the case of acetaminophen oxidation to N-
acetyl-p-quinoneimine, two electrons and two protons process
are involving [49,50].
Ipa
ð
l
AÞ ¼ ꢀ10:89 þ 12:36ðmVsꢀ1Þ1=2ðv in mVsꢀ1; R2 ¼ 0:999Þ
ð2Þ
In Fig 8, using pH controlled at 5.5, it is possible to observe the
electrochemical behavior of the GCE and GCE–Ru–AuNPs in the
acetaminophen detection, and in the Table 2 the reversibility elec-
trochemical parameters. The redox potential reversibility (DEp) of
Cyclic voltammogram obtained in CH3COONa solution
(0.1 mol Lꢀ1), without pH controlled, containing acetaminophen
in different concentration (99–654 l
mol Lꢀ1) showed a linear rela-
acetaminophen with GCE–Ru–AuNPs was improved 3.6 times
when compared to GCE, and the Ipa and Ipc were improved 1.43
and 1.67 times respectively. The stability of GCE–Ru–AuNPs was
tionship between the Ipa and the acetaminophen concentration,
which can be described by the Eq. (1) and Fig. 7. The sensibility
(S) and detection limit (DL) values were respectively:
Fig. 6. Thin film of [RuCl(dppb)(bipy)(4-vpy)]+ generated onto the surface of glassy
carbon electrode, scan rate = 100 mV/s, 10 cycles under potential cycling between
2.0 and ꢀ2.4 V in dichloromethane solution of TBAH (0.1 mol Lꢀ1).
Fig. 8. Cyclic voltammograms using GCE (dashed line) and GCE–Ru–AuNPs (solid
line) for acetaminophen detection (0.01 mol Lꢀ1
) )
in CH3COONa (0.1 mol Lꢀ1
solution as the electrolyte support at pH 5.5.

V.F. Ferreira et al. / Polyhedron 78 (2014) 46–53
53
Table 2
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Reversibility voltammograms parameters to acetaminophen detection: GCE and GCE–
Ru–AuNPs.
Electrochemical parameters
GCE
0.548
0.084
0.464
82.422
ꢀ35.394
GCE–Ru–AuNPs
Epa (V)
Epc(V)
0.515
0.386
0.129
117.822
ꢀ59.242
D
Ep (V)
Ipa
Ipc
(
l
A)
A)
(l
tested for 5 successive measurements of 0.01 mol Lꢀ1 acetamino-
phen in CH3COONa (0.1 mol Lꢀ1) solution at pH 5.5. Relative stan-
dard deviations (RSDs) of Epa and Ipa responses were 0.19% and
0.50% respectively, which suggests that the GCE–Ru–AuNPs has
high stability.
4. Conclusions
The interaction between [RuCl(dppb)(bipy)(py)]+ and AuNPsꢀ
was accompanied by SEM–EDS and TEM–EDS measurements, indi-
cating to be electrostatic interactions. Therefore it was used to add
AuNPs onto the surface of glassy carbon electrode (GCE), without
Au–S covalent bond. In toward of this view, a thin film of
[RuCl(dppb)(bipy)(4-vpy)]+ was generated onto the surface of
glassy carbon electrode (GCE), using cyclic voltammetry, by
adsorption and reduction of 4-vinylpyridine group. This step pro-
duced a glassy carbon–Ru+ electrode (GCE–Ru+), which was used
to incorporate a stable gold nanoparticles (AuNPs), with desired
shapes and sizes on the surface of electrode, by electrostatic inter-
action between GCE–Ru+ and AuNPsꢀ (GCE–Ru–AuNPs). The per-
formances of the GCEh and GCE–Ru–AuNPs were evaluated by
cyclic voltammetry for acetaminophen determination, having the
latter a high stability (Relative standard deviations (RSDs) of Epa
and Ipa responses were 0.19% and 0.50% respectively). The redox
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potential reversibility (DEp) of acetaminophen with GCE–Ru–AuN-
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also, the Epa response increases with the increase of the acetamino-
phen concentration at pH 5.5.
Acknowledgement
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We thank FAPEMIG, CNPq, CAPES, FAPESP, FINEP and RQ-MG
for financial support.
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Appendix A. Supplementary data
CCDC 987996 contains the supplementary crystallographic data
for the complex [RuCl(dppb)(5,50-Me-2,20-bipy)(4-vpy)]PF6. These
data can be obtained free of charge via http://www.ccdc.cam.ac.
uk/conts/retrieving.html, or from the Cambridge Crystallographic
Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44)
1223 336 033; or e-mail: deposit@ccdc.cam.ac.uk.
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