Solid-supported chemiluminescence and electrogenerated chemiluminescence based on a tris(2,2′-bipyridyl)ruthenium(II) derivative

Article abstract of DOI:10.1039/b511071h

We report a simple and efficient technique for the covalent immobilisation of a tris(2,2′-bipyridyl)ruthenium(ii) derivative suitable for both chemiluminescence and electrochemiluminescence detection. The Royal Society of Chemistry 2006.

Full text of DOI:10.1039/b511071h

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Solid-supported chemiluminescence and electrogenerated
chemiluminescence based on a tris(2,29-bipyridyl)ruthenium(II)
derivative{
G. M. Greenway, A. Greenwood, P. Watts and C. Wiles*
Received (in Cambridge, UK) 3rd August 2005, Accepted 18th October 2005
First published as an Advance Article on the web 11th November 2005
DOI: 10.1039/b511071h
Using methodology reported by Donnici et al.,13 2,29-bipyridine-
We report a simple and efficient technique for the covalent
immobilisation of a tris(2,29-bipyridyl)ruthenium(II) derivative
suitable for both chemiluminescence and electrochemilumines-
cence detection.
4,49-carboxylic acid 4 was synthesised in excellent yield (98%)
from commercially available 4,49-dimethyl-2,29-bipyridine 5.
Treatment of the resulting carboxylic acid 4 with thionyl
chloride 6 afforded the respective acid chloride 7 which was
subsequently reacted with 3-aminopropyltriethoxysilane 8, in
the presence of triethylamine 9, to afford 2,29-bipyridyl-
4,49-dicarboxylic acid bis[(3-triethoxysilylpropyl)amide] 10, in
96% yield.14 Ligand 10 was subsequently reacted with cis-
dichlorobis(bipyridine)ruthenium15 11 (synthesised in 63%
yield) to afford 4,49-bis[(3-triethoxysilylpropyl)amide]-
2,29-bipyridine]bis(2,29-bipyridine) ruthenium(II) dichloride 3
in high yield (73%) (Scheme 2).{ Consequently, by synthesis-
ing a compound that not only contained a ligand for cis-
dichlorobis(bipyridine)ruthenium 11 but also a linker, we
The inherent sensitivity and selectivity demonstrated by the
chemiluminescent reaction of tris(2,29-bipyridyl)ruthenium(III) 11
has led to its widespread application for the determination of
reducing species, in both static and flowing systems.2 A major
drawback of the technique, however is the need to constantly
supply the reagent to the site of reaction, increasing both analysis
costs and waste generated.
Scheme 1 Mechanism of [Ru(bipy)3]2+ 2 regeneration.
As Scheme
1 illustrates tris(2,29-bipyridyl)ruthenium(II) 2
([Ru(bipy)3]2+) is oxidised, either chemically3 (CL) or electro-
chemically4 (ECL), to afford [Ru(bipy)3]3+ 1 which is subsequently
reduced by an analyte, resulting in the emission of a photon of
light. As [Ru(bipy)3]2+ 2 is regenerated, immobilisation of the
chemiluminescent reagent would not only enable the reagent to be
recycled, leading to reduced analysis costs and waste generation,
but would also greatly simplify instrumental set-up.5 With these
factors in mind, many groups have attempted to immobilise
chemiluminescent reagents, using approaches such as the doping
of sol–gels,5,6 fabrication of composite films7 or more recently
the preparation of solid-supported derivatives.8 Problems with
these techniques, however, include a leaching of the reagent,9
instability to organic solvents10 and the inability to use the
immobilisation technique for both CL and ECL systems. To
address these problems, we describe herein an efficient technique
for the synthesis and covalent immobilisation of
a
tris(2,29-bipyridyl)ruthenium(II) derivative 3. Preliminary results
are subsequently reported for the detection of codeine12 using
complex 3 in both CL and ECL based systems.
Department of Chemistry, The University of Hull, Cottingham Road,
Hull, UK HU6 7RX. E-mail: c.wiles@chem.hull.ac.uk;
Fax: +44 (0) 1482 466416; Tel: +44 (0) 1482 466369
{ Electronic supplementary information (ESI) available: Experimental
details. See DOI: 10.1039/b511071h
Scheme 2 Reaction scheme illustrating the synthesis of
a
tris(2,29-bipyridyl)ruthenium(II) derivative 3 (R = CONH(CH2)3Si(OEt)3).
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Chem. Commun., 2006, 85–87 | 85

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proposed that the [Ru(bipy)3]2+ derivative
3
could be
Silicate sol–gels are glass-like materials synthesised via the acid
or base-catalysed hydrolysis, and subsequent polycondensation, of
alkoxides such as tetramethylorthosilicate (TMOS). Due to the
low temperature processing used for their fabrication, silicate sol–
gels can be readily doped with modifiers such as dyes,17 enzymes18
and as demonstrated herein, chemiluminescent reagents; the
resulting gels are then cast into monoliths, films or coatings
depending on the final application. As the dopant molecules are
often smaller than the pores within silicate sol–gels, leaching
frequently occurs; leading to irreproducible responses and a
limited sensor lifetime.17 With this in mind, many techniques
have been reported within the literature to overcome this
problem, these include the preparation of composite films, using
additives such as Nafion19 or titania,20 or attaching the dopant
to large anchor molecules such as dextran;21 few have
however, resulted in the fabrication of stable and reproducible
sensors.
In order to address this widespread problem, MacCraith et al.11
reported the synthesis of 4,49-bis[(3-triethoxysilylpropyl)amide]-
2,29-bipyridine]bis(2,29-bipyridine)ruthenium(II) dichloride 3 and
demonstrated its incorporation into a fluorescence based sensor
for oxygen determination. However, as we were interested in the
evaluation of tertiary amines by chemiluminescence, the approach
taken by MacCraith and co-workers11 could not be used as it was
essential that residual triethylamine 9 was removed from the
ruthenium complex 3. With this in mind, amide 10 was synthesised
and purified prior to complexation with cis-dichlorobis(bipyridine)
ruthenium 11, affording complex 3 in high yield (73%) and purity.
Alternatively, Lee et al.22 recently reported the synthesis of a
ruthenium derivative containing six trimethoxysilane moieties
suitable for ECL sensing at an ITO electrode. Although this
approach is advantageous as no tertiary amines are employed
during the synthesis, the resulting ruthenium complex is extremely
air sensitive and therefore undesirable. In comparison, the
ruthenium complex 3 described herein has been shown to be air
stable for in excess of eight months.
covalently immobilised onto a silica surface, by simple
hydrolysis of the triethoxysilane moieties (Fig. 1).
In order to evaluate the chemiluminescent properties of the
resulting ruthenium derivative 3, we initially investigated its
covalent immobilisation onto controlled pore glass (CPG),
whereby a free flowing orange material was obtained (2.61 6
1023 mmol Ru g21) (Fig. 1). The functionalised CPG 12 (0.050 g,
1.305 6 1023 mmol Ru) was subsequently packed into a flow cell
(Fig. 2) and its response to codeine (1 6 1023 M) evaluated using
sequential injection analysis (SIA) (Table 1). Using cerium(VI)
sulfate (0.1 M in 1.0 M sulfuric acid) as the oxidising agent,16 we
were able to confirm the successful immobilisation of a CL reagent
to CPG and its application to the detection of codeine, whereby an
average signal of 35.5 mV was obtained (RSD = 2.98%, n = 30)
with an analysis time of 60 s.
In comparison to the immobilised ruthenium derivative
described by Barnett and co-workers,8 no conditioning of the
immobilised reagent was found to be necessary in order to obtain a
steady response. Having successfully demonstrated the covalent
immobilisation of the tris(2,29-bipyridyl) ruthenium(II) derivative 3
to CPG, the investigation was extended to evaluate the
incorporation of complex 3 into a silicate sol–gel, enabling the
fabrication of a regenerable ECL sensor.
Fig. 1 Schematic illustrating the covalent immobilisation of
tris(2,29-bipyridyl)ruthenium(II) complex 3 onto a silica surface.
a
In brief,{ the organosilicate sol–gels were prepared using a
modified method described by Collinson et al.5 whereby a solution
of TMOS and the ruthenium derivative 3 (y6.5% wrt TMOS)
were hydrolysed in the presence of an acid catalyst (0.1 M aq.
HCl), followed by base catalysed gelation. In order to investigate
the leaching properties of the organosilicate sol–gels, monoliths
were prepared in addition to the dip coated electrodes. With
respect to monolith fabrication, gelation was induced by the
addition of aq. NaOH (1 6 1022 M) and the resulting sol–gel
cured in a dessicator for 24 h (in the absence of a vacuum), to
afford an orange translucent glassy material.{ Coated electrodes
were prepared by dipping a glassy carbon electrode into the
hydrolysed solution containing complex 3, withdrawing slowly to
leave a thin film; gelation was subsequently induced by placing the
electrode in borate buffer (pH 8.5, 0.1 M) for a period of 24 h in
order to age the film.
Fig. 2 Flow cell used for the evaluation of functionalised CPG 12.
Table 1 Description of the SIA parameters employed for the CL
evaluation of functionalised CPG 12
8
Reagent
Plug volume/ml
Using an ECL detection system built in-house,{ the coated
glassy carbon electrodes were placed in an electrochemical cell in
front of a photomultiplier tube. A three electrode potentiostat was
used to apply the required voltages and cyclic voltammetry
employed to assess the performance of the electrode. In order to
evaluate the ECL activity of the organosilicate sol–gel films, the
following operating conditions were used; sample volume 5 ml,
Cerium(VI) sulfate in H2SO4 (pH 1, 0.1 M)
Air gap
0.40 (10)a
0.20 (5)
0.40 (10)
0.20 (5)
1.00 (25)
0.20 (5)
Codeine in deionised water (1 6 1023 M)
Air gap
Deionised water
Air gap
a
Time intervals employed to obtain desired plug volumes/s.
86 | Chem. Commun., 2006, 85–87
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1 6 1023 M codeine, voltage range 0.7 to 1.3 V, step potential
0.0024 V and a scan rate of 0.01 V s21
Knight (NMR and ICP-MS), Dr Kevin Welham (MS) and Mr
Mike Bailey (flow cell fabrication), for their assistance with this
investigation.
.
Other groups report that when employing [Ru(bipy)3]2+ 2 doped
silicate sol–gel films, irreproducible ECL signals are obtained;
demonstrating an overall trend of decreasing signal with time; an
observation that can be attributed to leaching of the CL reagent.17
However, by covalently immobilising the CL reagent within a
silicate sol–gel, reproducible ECL signals of 7.7 mV (% RSD =
1.07, n = 24) were obtained. Although the ECL signals obtained are
not as great as those for the functionalised CPG 12, we are
currently investigating the incorporation of a greater proportion
of 4,49-bis[(3-triethoxysilylpropyl)amide]-2,29-bipyridine]bis(2,29-
bipyridine)ruthenium(II) dichloride 3 into the silicate sol–gels in
order to attain higher sensitivities.
Notes and references
{ To confirm covalent immobilisation of complex 3 into the silicate sol–gel
matrix, monoliths were prepared and stored in a range of commonly
employed solvent systems, including borate buffer (pH 8.5), phosphate
buffer (pH 7.0), aq. sulfuric acid (0.01 M) and acetonitrile; no leaching has
been observed over a period of 8 months.
1 D. M. Hercules and F. E. Lytle, J. Am. Chem. Soc., 1966, 88, 4745.
2 R. D. Gerardi, N. W. Barnett and S. W. Lewis, Anal. Chem. Acta, 1999,
378, 1.
3 R. D. Geradi, N. W. Barnett and P. Jones, Anal. Chim. Acta, 1999, 388,
1.
4 W. L. Wallace and A. J. Bard, J. Phys. Chem., 1979, 83, 1350.
5 M. M. Collinson and B. Novak, J. Sol-Gel Sci. Technol., 2002, 23, 215.
6 L. L. Schultz, J. S. Stoyanoff and T. A. Neiman, Anal. Chem., 1996, 68,
349.
7 H. Wang, G. Xu and S. Dong, Anal. Chim. Acta, 1992, 261, 64.
8 N. W. Barnett, R. Bos, H. Brand, P. Jones, K. F. Lim, S. D. Purcell and
R. A. Russell, Analyst, 2002, 127, 455.
In summary, compared to the physical entrapment of CL
reagents in silicate sol–gels, covalent immobilisation is advanta-
geous as it ensures homogeneous distribution of the reagent within
the matrix while preventing reagent leaching; resulting in reduced
analysis costs, reproducible analyte responses and extended sensor
lifetimes.
In conclusion, by synthesising a compound that acts as both a
ruthenium ligand and a hydrolysable linker, we have demonstrated
a simple and efficient technique for the covalent immobilisation of
a tris(bipyridyl)ruthenium derivative 3, suitable for employment in
both CL and ECL systems. In comparison to adsorption or
entrapment of the CL reagent, covalent immobilisation is
advantageous as no leaching is observed, leading to increased
reproducibility and sensor lifetime. This approach to immobilisa-
tion allows the CL reagent to be readily recycled, which is vital for
in situ sensor measurements. In addition to the applications
9 T. M. Downey and T. A. Nieman, Anal. Chem., 1992, 64, 261.
10 A. J. Tudos, J. J. Ozinga, H. Poppe and W. Th. Kok, Anal. Chem.,
1990, 62, 367.
11 C. Malins, S. Fanni, H. G. Glever, J. G. Vos and B. D. MacCraith,
Anal. Commun., 1999, 36, 3.
12 (a) N. W. Barnett, T. A. Bowser, R. D. Gerardi and B. Smith, Anal.
Chim. Acta, 1996, 318, 309; (b) G. M. Greenway, A. W. Knight and
P. J. Knight, Analyst, 1995, 120, 2459.
13 C. L. Donnici, D. H. M. Filho, L. L. C. Moreira, G. teixeira dos Reis,
E. S. Cordeiro, I. M. Ferreira de Oliveira, S. Carvalho and E. B. Paniago,
J. Braz. Chem. Soc., 1998, 9, 455.
14 A. Franville, D. Zambon and R. Mahiou, Chem. Mater., 2000, 12, 428.
15 G. Sprintschnik, H. W. Sprintschnik, P. P. Kirsch and D. G. Whitten,
J. Am. Chem. Soc., 1977, 4947.
16 B. A. Gorman, N. W. Barnett and R. Bos, Anal. Chim. Acta, 2005, 541,
117.
described
herein,
4,49-bis[(3-triethoxysilylpropyl)amide]-2,29-
bipyridine]bis(2,29-bipyridine)ruthenium(II) dichloride 3 could also
be employed for the functionalisation of other silica substrates
such as glass coils, micro channels, optical fibres and nanosensors.
With these factors in mind, work is currently underway within
our laboratories to ascertain the effect of 4,49-bis[(3-triethoxysilyl-
propyl)amide]-2,29-bipyridine]bis(2,29-bipyridine)ruthenium(II)
dichloride 3 concentration on the working range and detection
limits of the ECL technique.
17 T. M. Butler, B. D. MacCraith and C. McDonagh, J. Non-Cryst. Solids,
1998, 224, 249.
18 I. Gill and A. Ballesteros, J. Am. Chem. Soc., 1998, 120, 8587.
19 I. Rubinstein and A. J. Bard, J. Am. Chem. Soc., 1980, 102, 6642.
20 Y. Zhang and H. Ju, Electroanalysis, 2004, 16, 1401.
21 M. Plaschke, R. Czolk, J. Reichert and H. J. Ache, Thin Solid Films,
1996, 279, 233.
This work was financially supported by the RSC (A. G.). We
are grateful to, Mrs. Brenda Worthington (NMR), Mr Bob
22 J.-K. Lee, S.-H. Lee, M. Kim, H. Kim, D.-H. Kim and W.-Y. Lee,
Chem. Commun., 2003, 1602.
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Chem. Commun., 2006, 85–87 | 87