Immobilisation of alkylamine-functionalised osmium redox complex on glassy carbon using electrochemical oxidation

Article abstract of DOI:10.1016/j.electacta.2014.03.090

The electrochemical oxidation of alkylamines provides a method for modification of carbon, and other surfaces via formation of a radical amine that reacts with the surface. Direct electrochemical oxidation of an alkylamine functional group of a redox complex provides a simple route to preparation of a redox active layer on carbon surfaces. Here we report on oxidation of an osmium redox complex, containing an alkylamine ligand distal to the metal co-ordination site, on carbon electrodes to directly produce a redox active film on the surface. The presence of the redox-active layer of osmium complexes is confirmed by cyclic voltammetry and X-Ray photoelectron spectroscopy. The average surface coverage of the attached film upon electrolysis of an [Os(2,2′-bipyridine)₂(4-aminomethylpyridine)Cl].PF₆ complex is 0.84 (± 0.3) × 10^-10 moles cm^-2, demonstrating that coverages close to that predicted for a close-packed monolayer of complex is attained. The bioelectrocatalytic activity of the modified electrode was evaluated for oxidation of glucose in presence of glucose oxidase in solution. Hence, electrochemical coupling of alkylamine functionalised osmium redox complexes provides a simple and efficient methodology for obtaining redox active monolayers on carbon surfaces with potential applications to biosensor and biofuel cell device development.

Full text of DOI:10.1016/j.electacta.2014.03.090

G Model
EA-22406; No. of Pages8
ARTICLE IN PRESS
Electrochimica Acta xxx (2014) xxx–xxx
Contents lists available at ScienceDirect
Electrochimica Acta
journal homepage: www.elsevier.com/locate/electacta
Immobilisation of Alkylamine-Functionalised Osmium Redox
Complex on Glassy Carbon using Electrochemical Oxidation
Rakesh Kumar, Dónal Leech∗
School of Chemistry & Ryan Institute, National University of Ireland Galway, University Road, Galway, Ireland
a r t i c l e i n f o
a b s t r a c t
Article history:
The electrochemical oxidation of alkylamines provides a method for modification of carbon, and other
surfaces via formation of a radical amine that reacts with the surface. Direct electrochemical oxidation
of an alkylamine functional group of a redox complex provides a simple route to preparation of a redox
active layer on carbon surfaces. Here we report on oxidation of an osmium redox complex, containing
an alkylamine ligand distal to the metal co-ordination site, on carbon electrodes to directly produce a
redox active film on the surface. The presence of the redox-active layer of osmium complexes is con-
firmed by cyclic voltammetry and X-Ray photoelectron spectroscopy. The average surface coverage of
the attached film upon electrolysis of an [Os(2,2ꢀ-bipyridine)2(4-aminomethylpyridine)Cl].PF6 complex
is 0.84 ( 0.3) × 10−10 moles cm−2, demonstrating that coverages close to that predicted for a close-
packed monolayer of complex is attained. The bioelectrocatalytic activity of the modified electrode was
evaluated for oxidation of glucose in presence of glucose oxidase in solution. Hence, electrochemical
coupling of alkylamine functionalised osmium redox complexes provides a simple and efficient method-
ology for obtaining redox active monolayers on carbon surfaces with potential applications to biosensor
and biofuel cell device development.
Received 16 December 2013
Received in revised form 13 March 2014
Accepted 14 March 2014
Available online xxx
Keywords:
Osmium
Electrografting
Redox monolayer
Modified electrode
Glucose detection.
© 2014 Elsevier Ltd. All rights reserved.
1. Introduction
Apart from free radical grafting, formation of self-assembled mono-
layers (SAMs) using thiol chemistry on gold electrodes provides
Modification of carbon electrode surfaces with redox layers is of
interest to many application areas, such as biosensors, molecular
electronics, biofuel cell devices and electrocatalysis [1,2]. Modifi-
cation of surfaces can provide new properties to a surface while
maintaining the bulk properties [3] with potential use for both
analytical and chemical sensing [4]. The ability to form strongly-
bonded, stable, monolayers on carbon surfaces is attractive for
molecular device and sensor applications [5,6]. In addition, sur-
face immobilised molecules which are capable of heterogeneous
electron transfer between redox centre and surface can have high
impact on the rapidly emerging field of high speed molecular elec-
tronics applications [7,8].
Various methods have been described for modification of carbon
surfaces through a free radical grafting mechanism. For example,
covalent modification of surfaces via reduction of aryldiazonium
salts can lead to functionalised electrodes with high stability
[2,9,10]. A major disadvantage to this approach is that synthesis and
isolation of the diazonium salt is not always straightforward [11].
another way for introduction of chemical functionality to surfaces.
However, the Au-thiol chemistry has several drawbacks such as
thermal instability, prone to UV photo-oxidation [12] and mobil-
ity of layer results in a decreased electrochemical signal for many
possible applications [10,13,14].
The covalent attachment of alkylamines to carbon and metallic
surfaces using an electro-oxidation method has been reviewed in
detail by Pinson and colleagues in recent years [15,16] and proven
to be an excellent method for surface modification [17]. The extent
of surface derivatisation depends upon the degree of substitution
at the amine functionality [18], as tertiary amines show no evi-
dent surface coverage, compared to primary and secondary amines,
proposed to be because of the steric hindrance which blocks the
accessibility of amine radicals to surfaces [6,19].
Osmium and ruthenium based polypyridyl complexes are
broadly explored for a range of applications as redox cata-
lysts and mediators, due to the ease of synthetic variation of
structure and therefore properties of these complexes [20]. For
example, the redox potential of osmium based complexes can
be tuned across a wide potential window by altering the lig-
and of a complex [21,22]. The favourable relatively low redox
potential of osmium complexes and their relative stability in
∗
Corresponding author.
E-mail address: Donal.leech@nuigalway.ie (D. Leech).
http://dx.doi.org/10.1016/j.electacta.2014.03.090
0013-4686/© 2014 Elsevier Ltd. All rights reserved.
Please cite this article in press as: R. Kumar, D. Leech, Immobilisation of Alkylamine-Functionalised Osmium Redox Complex on Glassy
Carbon using Electrochemical Oxidation, Electrochim. Acta (2014), http://dx.doi.org/10.1016/j.electacta.2014.03.090

G Model
EA-22406; No. of Pages8
ARTICLE IN PRESS
2
R. Kumar, D. Leech / Electrochimica Acta xxx (2014) xxx–xxx
both oxidation states (II/III) is advantageous over the iron and
ruthenium based systems [23]. Surface confined osmium based
complexes are capable of mediating electron transfer to/from
enzymatic [24,25] as well as microbial systems [26,27] on elec-
trodes.
2ꢀ-bipyridine)2(4-aminomethylpyridine)Cl].PF6: C, 39.86%; H,
3.25%; N, 10.23% compared to theoretical values: C, 39.47%; H,
3.06%; N, 10.62%.
Prior to modification, GC disk electrodes were polished with
1 ␮m, 0.3 ␮m, and 0.05 ␮m of alumina slurry on microcloth pads
(Buehler) followed by rinsing with Milli-Q-water and drying with
nitrogen gas stream. The glassy carbon plate and PPF electrode
were cleaned by sonicating in acetonitrile for 15 minutes. All exper-
iments were carried out at room temperature unless otherwise
stated.
In the present paper, we report on direct grafting of an osmium
complex,
[Os(2,2ꢀ-bipyridine)2(4-aminomethylpyridine)Cl].PF6
(Osbpy4AMP), to glassy carbon and pyrolysed photoresist (PPF)
surfaces by the simple methodology of electrochemical oxidation
of the alkylamine functional group of the complex. Previously
Buriez et al. [28] grafted a redox layer of amino-ferrocifen to
carbon and metal surfaces based on electro-oxidation of the
aryl-amine group of the organometallic complex, yielding strong
attachment of the redox complex to surfaces [28]. Aramata
et al. [29] grafted ligands of redox complexes onto carbon elec-
trodes, using electro-oxidation of amine-containing ligands, to
provide a platform for preparation of redox layers on carbon
electrodes. Direct electro-oxidation of an osmium metal complex
containing an aryl-amine ligand (4-aminopyridine) for graft-
ing to carbon was also briefly described [29]. More recently,
osmium polypyridyl complexes have been grafted to carbon
surfaces to provide redox layers capable of mediating electron
transfer to a glucose-oxidising enzyme in solution [30]. Details
of the direct grafting of Osbpy4AMP to carbon surfaces by sim-
ple electro-oxidation of the alkylamine group is reported on
here. The resulting modified surface is characterised by cyclic
voltammetry (CV) and X-ray Photoelectron Spectroscopy (XPS).
The experimental results demonstrate that a monolayer of redox
complex is formed that is stable and can be used as a mediating
surface for glucose oxidation by glucose oxidase in solution. Use
of this chemical coupling methodology can provide a simple route
for modification of a surface with a variety of osmium redox
complexes for application to biosensor and biofuel cell device
development.
2.1. Apparatus
All electrochemical measurements were performed using a CHI
620 potentiostat in a conventional three electrode cell. XPS was
carried out using a Kratos AXIS 165 spectrometer with the fol-
lowing parameters: Sample Temperature: 20-30 ◦C, X-Ray Gun:
mono Al K␣ 1486.58 eV; 150 W (10 mA, 15 kV), Pass Energy: 160 eV
for survey spectra and 20 eV for narrow regions. Step: 1 eV (sur-
vey), 0.05 eV (regions), Dwell: 50ms (survey), 100 ms (regions),
Sweeps: survey (4), narrow regions (5-20). For calibration the C
1s line at 284.8 eV was used as charge reference for determining
binding energies. Other spectra were collected in the normal to
the surface direction. XPS detection limit is estimated to be ∼0.1
at%. Quantitative survey spectra were obtained on high resolution
spectra of elements acquired. The measurements were taken at
take-off angle of 30o (sample tilt 60o) for better surface sensitiv-
ity.
3. Results and discussion
3.1. Electrochemically induced attachment of alkylamine
functionalised redox complex to carbon surface.
Prior to surface confinement, solution phase cyclic voltam-
metry (CV) is used to evaluate the redox potential for the Os(II/III)
transition of the Osbpy4AMP complex. Characteristic oxidation
and reduction peaks are observed centred at 0.34 V (vs. Ag/AgCl),
Fig. 1a, for 0.1 mM Osbpy4AMP in acetonitrile solution contain-
ing 0.1 M tetraethylammonium tetrafluoroborate as electrolyte. A
formal potential of 0.30 V vs. Ag/AgCl can be estimated for the
Os(II/III) transition from CV in aqueous phosphate buffer (pH 7.4);
a value that is similar to that observed by others for the complex in
buffer solution [35]. The electrochemically induced attachment of
Osbpy4AMP to carbon surfaces was performed via oxidation of the
alkylamine functional group of the complex, in acetonitrile solu-
tion containing 0.1 M of tetraethylammonium tetrafluoroborate
as electrolyte. The consecutive cyclic voltammograms of 0.1 mM
Osbpy4AMP show a broad electrochemically irreversible peak
appearing at around 1.9 V vs. Ag/AgCl in the potential window
from 1.5 to 2.1 V. The peak current decreases with multiple voltam-
metric scans recorded at 0.1 Vs−1. This peak is attributed to the
one electron electrochemical oxidation of the alkylamine with for-
mation of an amine radical that can covalently couple to glassy
carbon and pyrolysed photoresist (PPF) surfaces, as depicted in
Scheme 1. Under continuous cycling the magnitude of peak cur-
rent decreases, as observed by others [6,18], and as shown in
Fig. 1(b). This is proposed to be as a result of a decrease in avail-
ability of surface area for coupling once the first scan, and coupling
process, is undertaken [6,18], thus indicating coupling reaction at
electrode surfaces [15,17,36]. The redox potential for the oxida-
tion is in agreement with data for oxidation of alkylamines and
mono-Boc-protected diamine compounds at glassy carbon elec-
trodes [6,17,37].
2. Experimental
All chemicals were purchased from Sigma-Aldrich and used
without any further purification. All solutions were prepared in
Milli-Q (18.2 Mꢀ cm) water unless otherwise stated. Either glassy
carbon disk (GC, 3 mm diameter) or plate (25 × 25 × 1 mm) work-
ing electrodes were used along with a platinum wire counter
electrode and an Ag/AgCl (3 M KCl) reference electrode in a
10 mL single compartment electrochemical cell (all sourced from
IJ Cambria). The pyrolysed photoresist (PPF) working electrodes
(approximately 15 mm × 15 mm) were a gift from Alison Dow-
nard, University of Canterbury. The PPF were fabricated using two
coats of photoresist which were spin coated onto silicon wafer
followed by soft baked before pyrolyzing at 1050 ◦C [31,32]. For
the modification of PPF surface, the electrodes were mounted on
an insulated metal stage with four springs. A hole in the bot-
tom was positioned on top of a Viton O-ring that sealed the
solution above the electrode. Phosphate buffered saline (PBS),
pH 7.4, was prepared using 50 mM phosphate buffer with 0.1 M
NaCl. Glucose oxidase type VII from Aspergillus niger (GOx, EC
1.1.3.4., average activity 180 unit/mg) was purchased from Sigma-
Aldrich.
[Os(2,2ꢀ-bipyridine)2(4-aminomethylpyridine)Cl].PF6
synthesised according to literature methods [33] based on
the 4-aminomethylpyridine (4-AMP) ligand substitution of
chloride by heating an ethylene glycol solution of a 1.1 mole
equivalent ligand and Os(2,2ꢀ-bipyridyl)2Cl2 complex at reflux,
with precipitation of the resulting complex by addition of an
aqueous NH4PF6 solution [34]. Final product was filtered and
allowed to dry overnight at 50 ◦C. Microanalysis for [Os(2,
was
a
Please cite this article in press as: R. Kumar, D. Leech, Immobilisation of Alkylamine-Functionalised Osmium Redox Complex on Glassy
Carbon using Electrochemical Oxidation, Electrochim. Acta (2014), http://dx.doi.org/10.1016/j.electacta.2014.03.090

G Model
EA-22406; No. of Pages8
ARTICLE IN PRESS
R. Kumar, D. Leech / Electrochimica Acta xxx (2014) xxx–xxx
3
Scheme 1. Scheme depicting the proposed mechanism for electrochemically induced coupling of Osbpy4AMP to a glassy carbon surface.
3.2. Characterization of redox complex modified surface
to adsorbed electrode films or to graphite electrodes [35,38,39],
indicating that the redox potential of the Os(II/III) transition is gen-
erally not affected by immobilisation [21]. The anodic and cathodic
peak currents increase linearly with scan rate, as expected for a
surface-confined redox species, Fig. 2b [40].
The CVs of the surface bound complex at pH 7.4 in PBS shows
non-ideal peak separation, greater than zero, particularly at higher
scan rates, and a full-width at half-maximum of 160 mV, greater
than the value for an ideal monolayer of a redox complex on an
Cyclic voltammetry can be used to evaluate if the redox com-
plex is surface confined. The modified surface was cleaned with
ultrapure millipore water, sonicated for 2 minutes and then voltam-
mograms recorded in 0.05 M of phosphate buffer saline (pH 7.4),
Fig. 2a. The redox potential for the Os(II/III) transition is 0.3 V vs
Ag/AgCl similar to that for the complex in solution and coupled
Fig. 1. Cyclic voltammograms of solution of 0.1 mM [Os (2,2ꢀ-bipyridine)2(4-
aminomethylpyridine)Cl].PF6 in 0.1 M TEATFB in acetonitrile at a scan rate 0.1 Vs−1
(a) with a potential window selected to show the Os(II/III) transition and (b) the
electrochemical oxidation of the alkylamine (8 repeated cycles).
Fig. 2. (a) Cyclic voltammograms of a modified glassy carbon electrode in 0.05 M
PBS (pH 7.4) at scan rates of 10 (black), 30 (red), 50 (green) and 80 (blue) mVs−1. (b)
Plot of anodic and cathodic peak current, extracted from cyclic voltammograms of
a modified glassy carbon electrode, versus scan rate (Vs−1).
Please cite this article in press as: R. Kumar, D. Leech, Immobilisation of Alkylamine-Functionalised Osmium Redox Complex on Glassy
Carbon using Electrochemical Oxidation, Electrochim. Acta (2014), http://dx.doi.org/10.1016/j.electacta.2014.03.090

G Model
EA-22406; No. of Pages8
ARTICLE IN PRESS
4
R. Kumar, D. Leech / Electrochimica Acta xxx (2014) xxx–xxx
(a)
12
10
8
6
4
2
0
0
1
2
3
4
5
6
7
8
9
10
Voltammetric cycles
(b)
1.4
1.2
1
0.8
0.6
0.4
0.2
0
0
10
20
30
40
50
60
70
Time / h
Fig. 3. Surface coverage of osmium complexes calculated from cyclic voltammetric peaks of modified glassy carbon electrodes at 0.1 Vs−1 scan rate in 0.05 M PBS buffer (pH
7.4) as a function of (a) continuous voltammetric cycling and (b) a single voltammetric cycle with storage of electrode in buffer (pH 7.4) at room temperature between scans.
2 V, is 0.75 ( 0.2) × 10−10 moles cm−2. No trend in ꢁ Os as a func-
electrode surface [40]. This deviation may be attributed to a com-
bination of lateral interactions within the films [41]. The surfaces
coverage (ꢁ Os) of osmium can be calculated by integration of the
charge passed under the oxidation peak (after baseline correction):
tion of the number of CV cycles used in the preparation method is
apparent. Electrochemical grafting under these conditions is thus
independent of the number of cycles used. This is in agreement
with a report that electrografting of primary alkyl amines to car-
bon surfaces through repetitive cycling or scanning to more positive
potential ranges does not increase the surface coverage, as calcu-
lated from the N/C value using XPS [18]. Moreover, the final surface
coverage of osmium complex does not scale with scan rate, in
the range 0.06 Vs−1 to 0.5 Vs−1 when three CV cycles are used
ꢁOs = Q/nFA
(1)
Where Q is the charge, F is the Faraday constant, n is number of
electrons transferred, and A is area of the electrode.
The average ꢁ Os value obtained from modified electrodes, pre-
pared by cycling for one, three, or five cycles at 0.1 Vs−1 from 1.5 to
Please cite this article in press as: R. Kumar, D. Leech, Immobilisation of Alkylamine-Functionalised Osmium Redox Complex on Glassy
Carbon using Electrochemical Oxidation, Electrochim. Acta (2014), http://dx.doi.org/10.1016/j.electacta.2014.03.090

G Model
EA-22406; No. of Pages8
ARTICLE IN PRESS
R. Kumar, D. Leech / Electrochimica Acta xxx (2014) xxx–xxx
5
Fig. 4. XPS survey scans (a) at 30◦ (red) and 60◦ (green) and (b) N1s core fitting peak of a glassy carbon plate surface modified electrode by grafting of Osbpy4AMP.
2.0 × 10−6 C the equivalent of 2.1 × 10−11 moles of amine elec-
trolysed in a one-electron oxidation, that results in formation of
a layer on the electrode surface comprised of 6.7 × 10−12 moles
of the osmium complex corresponding to surface coverage of
for electrochemically induced coupling of the complex to carbon
electrodes, with an average ꢁ Os of 0.84 ( 0.3) × 10−10 moles cm−2
.
Integration of the charge for amine oxidation, for the low-
est charge passed for one cycle at 0.5 Vs−1 gives an estimate of
Please cite this article in press as: R. Kumar, D. Leech, Immobilisation of Alkylamine-Functionalised Osmium Redox Complex on Glassy
Carbon using Electrochemical Oxidation, Electrochim. Acta (2014), http://dx.doi.org/10.1016/j.electacta.2014.03.090

G Model
EA-22406; No. of Pages8
ARTICLE IN PRESS
6
R. Kumar, D. Leech / Electrochimica Acta xxx (2014) xxx–xxx
0.6
0.5
0.4
0.3
0.2
0.1
0.0
-0.1
-0.2
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
0.5
Potential vs. (Ag/AgCl) / V
Fig. 5. CV recorded at modified, by electrografting Osbpy4AMP, glassy carbon electrode in 0.5 ml PBS buffer (0.05 M, pH 7.4, 37 ◦C) containing glucose oxidase (9 U) in the
absence (red curve) and in the presence (blue curve) of 0.1 M glucose, at a scan rate of 5 mV s−1
.
0.9 × 10−10 moles cm−2. The primary amine radical cations formed
The short term stability of the osmium complex at the surface
is tested by undertaking repetitive CV cycles (Fig. 3a) at 0.1 Vs−1
scan rate in 0.05 M PBS buffer, with no change in the osmium
surface coverage over the 10 cycle testing period. Longer-term
stability to storage conditions is estimated from cyclic voltam-
mograms recorded in buffer with storage intervals in buffer
solution under room temperature, Fig. 3b. In this case, initially
there is a loss in redox signal of immobilised complex of approxi-
mately 27% over a 4 hour period. This may be attributed to the loss
of physisorbed molecules, as the decay profile does not follow a
simple single-exponential fit, indicating that more than one pro-
cess, or population of redox complex, may be responsible for the
change in surface coverage as a function of storage time. Follow-
ing this initial change, the surface coverage signal remains steady,
losing only an average of 17% of the signal at 4 hours over the next
70 hours of storage.
after electro-oxidation are reportedly more unstable [17], thus
more reactive, compared to secondary or tertiary amines, thus sug-
gesting that passage of lower charge in the electro-oxidation may
be necessary to probe for an effect on final surface coverage of the
osmium complex.
From the average osmium complex surface coverage of 0.84
(
0.3) × 10−10 moles cm−2 an area per molecule of osmium
complex of approximately 197 Å2 can be estimated, presum-
ing complete monolayer coverage on a smooth surface. This
is in reasonably good agreement with a projected area of 180
Å2 estimated from crystallographic data, considering a radius
˚
of osmium polypyridyl complexes of 7.5 A [42]. For compari-
son, an area per molecule of osmium polypyridyl complexes
self-assembled as a monolayer on platinum electrode surfaces
of approximately 240 Å2 was reported, with a redox complex
surface coverage of 1 × 10−10 moles cm−2 [43]. Thus, the pro-
posed electrochemical coupling procedure produces a relatively
compact redox active layer, at close to monolayer coverage. Multi-
layer formation may be possible, but given the surface coverage
is not likely, as reported on by others for surface grafting via
electro-reduction of aryl diazonium salts [9,38,44]. The osmium
surface coverages reported here are in good agreement with sur-
face coverages reported for monolayers of osmium complexes
self-assembled on platinum and gold [10,37,38,43] and a surface
coverage of 3.5 × 10−10 moles cm−2 for attachment of a ferrocene
complex to a bromophenyl-modified carbon electrode [45] and
to a surface coverage of 2.1 × 10−10 moles cm−2 for attachment
of a copper complex to a gold surface using an aryldiazonium
salt reduction method [46], while Boland et al. reported that
attachment of the Osbpy4AMP osmium complex to a carboxylic
acid-terminated carbon electrode using carbodiimide coupling
yielded a surface coverage of 2.9 × 10−10 moles cm−2 [10]. For
comparison, Buriez et al. [28] reported the surface coverage of
2.7 × 10−10 moles cm−2 for amino-ferrocifen complexes while Ara-
mata et al. [29] reported a surface coverage of 1.7 × 10−10 moles
cm−2 for grafting of an arylamine osmium complex on carbon sur-
faces.
The XPS results recorded after grafting of the osmium complex
to glassy carbon plates confirms the presence of the complex on
the surface. The survey scan of the modified glassy carbon surface,
prepared by cycling for 3 cycles over a potential range from 1.5
to 2.0 V vs. Ag/AgCl in 1 mM Osbpy4AMP dissolved in ACN at 0.1
Vs−1 is shown in Fig. 4a. The spectrum exhibits the characteris-
tic peaks for C 1s, N 1s and O 1s at 284.21, 400.5 and 532.21 eV,
respectively. The presence of N, Os, and Cl XPS peaks for the mod-
ified surface is a clear indication that the Os complex is present
on the carbon substrate. The peak F 1s at 685 eV corresponds to
the fluoride (PF6) present in the osmium complex salt. The Si 2p
peak at 102 eV is assigned to adventitious substrate impurities,
as reported on previously for XPS of carbon surfaces [47,48]. The
origin of the S 2p peak at 167 eV is not as yet identified, but may
also likely have arisen by adventitious substrate contamination. The
high resolution XPS scan of the N 1S region, Fig. 4b, for the modified
electrode surface shows a peak at 399.6 eV, has been attributed to
the N in bipyridine [49,50], while the component close to 400.5 eV
is reported to correspond to an amine functional group. The higher
energy peak around 402.0 eV may be due to protonation of the
amine during the grafting process [17]. The atomic % ratio of N 1s/C
1s, after correction for instrumental sensitivity is 0.044, compared
Please cite this article in press as: R. Kumar, D. Leech, Immobilisation of Alkylamine-Functionalised Osmium Redox Complex on Glassy
Carbon using Electrochemical Oxidation, Electrochim. Acta (2014), http://dx.doi.org/10.1016/j.electacta.2014.03.090

G Model
EA-22406; No. of Pages8
ARTICLE IN PRESS
R. Kumar, D. Leech / Electrochimica Acta xxx (2014) xxx–xxx
7
to a reported ratio for bare glassy carbon of 0.014 [6] once again
providing evidence of the presence of the complex at the sur-
face.
(HEA) through the Programme for Research at Third-Level Insti-
tutions, Cycle 5 (PRTLI-5), co-funded by the European Regional
Development Fund (ERDF). We are grateful to Dr. Fathima Laffir
of MSSI, University of Limerick for recording XPS spectra.
3.3. Bioelectrocatalysis for glucose oxidation
References
Osmium redox complexes are commonly used as mediators
in research and development of glucose biosensors [12,51] and
glucose oxidising enzymatic biofuel cells [35,52]. Clark et al. devel-
oped the first enzyme based amperometric electrode in 1961 [42],
and since then enzyme based electrode sensors have received
great attention for application to glucose detection. As the redox
active site of glucose oxidase is buried inside the insulating pro-
tein shell it is difficult to capture electron flow from the active
site of enzyme as a result of glucose oxidation, to deliver them
to the electrode, in so-called third generation biosensors devices
[52]. The redox mediator is used, in second generation glucose
biosensors, to shuttle electrons from the enzyme active site to
the electrode surface. Redox mediator utilisation in enzyme-
based electrodes allows for increased sensitivity, selectivity, and
detection of analyte at lower overpotentials in many applications
ranging from industry, environmental, energy to clinical applica-
tions [12,24,52].
The electrode surface modified by electrografting of an osmium
complex was therefore examined in a preliminary test for its
ability to mediate electron transfer from glucose oxidase, in
solution, as a result of glucose oxidation. The response of the
osmium complex modified electrode was evaluated using slow
scan cyclic voltammetry in phosphate buffer solution (pH 7.4,
37 ◦C), Fig. 5. The modified electrode exhibited in the absence
of substrate a CV signal with a pair of redox peaks centred at
0.3 V vs Ag/AgCl, indicating the presence of the osmium com-
plex on the surface. Upon addition of glucose at saturation
levels (0.1 M in the electrochemical cell), the cyclic voltammet-
ric response altered with an increase in the oxidation current
accompanied by a decrease in the reduction current, correspond-
ing to a catalytic response [20,40], demonstrating the possibility
of using the electrografting methodology to prepare, and com-
pare, a range of redox complex modified electrodes for screening
for application to biosensor or biofuel cell device develop-
ment.
[1] A.J. Downard, Electroanalysis 12 (2000) 1085–1096.
[2] X. Li, Y. Wan, C. Sun, Electroanal Chem 569 (2004) 79–87.
[3] K.H. Vase, A.H. Holm, S.U. Pedersen, K. Daasbjerg, Langmuir 21 (2005)
8085–8089.
[4] B.D. Bath, H.B. Martin, R.M. Wightman, M.R. Anderson, Langmuir 17 (2001)
7032–7039.
[5] S. Ababou-Girard, H. Sabbah, B. Fabre, K. Zellama, F. Solal, C. Godet, The Journal
of Physical Chemistry C 111 (2007) 3099–3108.
[6] M.A. Ghanem, J.-M. Chretien, A. Pinczewska, J.D. Kilburn, P.N. Bartlett, Journal
of Materials Chemistry 18 (2008) 4917–4927.
[7] R.J. Forster, E. Figgemeier, P. Loughman, A. Lees, J. Hjelm, J.G. Vos, Langmuir 16
(2000) 7871–7875.
[8] J.F. Smalley, H.O. Finklea, C.E.D. Chidsey, M.R. Linford, S.E. Creager, J.P. Ferraris,
K. Chalfant, T. Zawodzinsk, S.W. Feldberg, M.D. Newton, Journal of the American
Chemical Society 125 (2003) 2004–2013.
[9] D.J. Garrett, P. Jenkins, M.I.J. Polson, D. Leech, K.H.R. Baronian, A.J. Downard,
Electrochim Acta 56 (2011), 8-8.
[10] S. Boland, F. Barriere, D. Leech, Langmuir 24 (2008) 6351–6358.
[11] S. Baranton, D. Bélanger, The Journal of Physical Chemistry B 109 (2005)
24401–24410.
[12] M.H. Schoenfisch, J.E. Pemberton, Journal of the American Chemical Society 120
(1998) 4502–4513.
[13] C.D. Bain, E.B. Troughton, Y.T. Tao, J. Evall, G.M. Whitesides, R.G. Nuzzo, Journal
of the American Chemical Society 111 (1989) 321–335.
[14] C.D. Bain, J. Evall, G.M. Whitesides, Journal of the American Chemical Society
111 (1989) 7155–7164.
[15] J. Pinson, F. Podvorica, Chemical Society Reviews 34 (2005) 429–439.
[16] D. Belanger, J. Pinson, Chemical Society Reviews 40 (2011) 3995–4048.
[17] A. Adenier, M.M. Chehimi, I. Gallardo, J. Pinson, N. Vilà, Langmuir 20 (2004)
8243–8253.
[18] R.S. Deinhammer, M. Ho, J.W. Anderegg, M.D. Porter, Langmuir 10 (1994)
1306–1313.
[19] C. Combellas, F. Kanoufi, J. Pinson, F.I. Podvorica, Journal of the American Chem-
ical Society 130 (2008) 8576–8577.
[20] D. Leech, P. Kavanagh, W. Schuhmann, Electrochimica Acta 84 (2012)
223–234.
[21] P. Ó Conghaile, D. MacAodha, B. Egan, P. Kavanagh, D. Leech, Journal of The
Electrochemical Society 160 (2013) G3165–G3170.
[22] A.B.P. Lever, Inorganic Chemistry 29 (1990) 1271–1285.
[23] R.J. Forster, J.G. Vos, Macromolecules 23 (1990) 4372–4377.
[24] K. Habermüller, A. Ramanavicius, V. Laurinavicius, W. Schuhmann, Electroanal-
ysis 12 (2000) 1383–1389.
[25] P. Kavanagh, S. Boland, P. Jenkins, D. Leech, Fuel Cells 9 (2009) 79–84.
[26] U.A.S. Timur, D. Odaci, L. Lo Gorton, Electrochem. Commun 9 (2007).
[27] I. Vostiar, E.E. Ferapontova, L. Gorton, Electrochemistry Communications 6
(2004) 621–626.
[28] O. Buriez, E. Labbé, P. Pigeon, G. Jaouen, C. Amatore, Journal of Electroanalytical
Chemistry 619–620 (2008) 169–175.
4. Conclusion
[29] A. Aramata, S. Takahashi, G. Yin, Y. Gao, Y. Inose, H. Mihara, A. Tadjeddine,
W.Q. Zheng, O. Pluchery, A. Bittner, A. Yamagishi, Thin Solid Films 424 (2003)
239–246.
[30] S. Tsujimura, A. Katayama, K. Kano, Chemistry Letters 35 (2006)
1244–1245.
[31] S.S.C. Yu, A.J. Downard, Langmuir 23 (2007) 4662–4668.
[32] P.A. Brooksby, A.J. Downard, Langmuir 20 (2004) 5038–5045.
[33] E.M. Kober, J.V. Caspar, B.P. Sullivan, T.J. Meyer, Inorganic Chemistry 27 (1988)
4587–4598.
[34] C. Danilowicz, E. Cortón, F. Battaglini, Journal of Electroanalytical Chemistry
445 (1998) 89–94.
[35] S. Boland, P. Kavanagh, D. Leech, ECS Transactions 13 (2008) 77–87.
[36] J.K. Kariuki, M.T. McDermott, Langmuir 15 (1999) 6534–6540.
[37] M. Delamar, R. Hitmi, J. Pinson, J.M. Saveant, Journal of the American Chemical
Society 114 (1992) 5883–5884.
[38] S. Boland, K. Foster, D. Leech, Electrochimica Acta 54 (2009) 1986–1991.
[39] P. Ó Conghaile, S. Kamireddy, D. MacAodha, P. Kavanagh, D. Leech, Anal Bioanal
Chem 405 (2013) 3807–3812.
[40] J. Allen, L.R. Bard, Faulkner, Electrochemical Methods: Fundamentals and Appli-
cations, 2 ed., JOHN WILEY & SON, INC, 2001.
[41] E. Laviron, Journal of Electroanalytical Chemistry 100 (1979) 263–270.
[42] H. Goodwin, D. Kepert, J. Patrick, B. Keltn, A. White, Australian Journal of Chem-
istry 37 (1984) 1817–1824.
Carbon electrode surfaces are modified via electrochemical
coupling of an alkylamine functional group of an osmium-based
redox complex in a simple procedure. Cyclic voltammetry and
XPS data indicates the presence of the osmium complex at the
surface. The modified electrode showed electrocatalytic activity
for oxidation of glucose in presence of glucose oxidase. The same
modification strategy may be extended to provide a simple route
for immobilisation of a range of redox complexes that possess
an alkylamine functional group distal to the central metal atom
to explore the effect of structure and complex redox potential
on the surface coverage of complex and electrocatalytic appli-
cations of the resulting redox layers. For example, the modified
surfaces could have application in a wide range of biosensor and
biofuel cell electrochemical devices, as well as exploring the use
of redox layers for light-harvesting or water-splitting applica-
tions.
[43] R.J. Forster, L.R. Faulkner, Journal of the American Chemical Society 116 (1994)
5444–5452.
Acknowledgements
[44] J.K. Kariuki, M.T. McDermott, Langmuir 17 (2001) 5947–5951.
[45] O. Ghodbane, G. Chamoulaud, D. Bélanger, Electrochemistry Communications
6 (2004) 254–258.
We acknowledge funding from the Earth and Natural Science
Doctoral Studies Programme, of the Higher Education Authority
Please cite this article in press as: R. Kumar, D. Leech, Immobilisation of Alkylamine-Functionalised Osmium Redox Complex on Glassy
Carbon using Electrochemical Oxidation, Electrochim. Acta (2014), http://dx.doi.org/10.1016/j.electacta.2014.03.090

G Model
EA-22406; No. of Pages8
ARTICLE IN PRESS
8
R. Kumar, D. Leech / Electrochimica Acta xxx (2014) xxx–xxx
[46] G. Liu, T. Böcking, J.J. Gooding, Journal of Electroanalytical Chemistry 600 (2007)
335–344.
[50] C. Ferragina, M. Massucci, G. Mattogno, J Incl Phenom Macrocycl Chem 7 (1989)
529–536.
[47] R.C. Engstrom, V.A. Strasser, Analytical Chemistry 56 (1984) 136–141.
[48] S.E. Creager, B. Liu, H. Mei, D. DesMarteau, Langmuir 22 (2006)
10747–10753.
[51] W. Schuhmann, T.J. Ohara, H.L. Schmidt, A. Heller, Journal of the American
Chemical Society 113 (1991) 1394–1397.
[52] P. Kavanagh, D. Leech, Physical Chemistry Chemical Physics 15 (2013)
4859–4869.
[49] B.J. Lindberg, J. Hedman, Chemica Scripta 7 (1975) 155.
Please cite this article in press as: R. Kumar, D. Leech, Immobilisation of Alkylamine-Functionalised Osmium Redox Complex on Glassy
Carbon using Electrochemical Oxidation, Electrochim. Acta (2014), http://dx.doi.org/10.1016/j.electacta.2014.03.090