Anal. Chem. 2010, 82, 2401–2404
1-Ethyl-3-Methylimidazolium Ethylsulfate/Copper
Catalyst for the Enhancement of Glucose
Chemiluminescent Detection: Effects on Light
Emission and Enzyme Activity
Aure´ lie A.-M. Santafe´ , Bastien Doume` che, Loïc J. Blum, Agne` s P. Girard-Egrot, and
Christophe A. Marquette*
Laboratoire de Ge´nie Enzymatique, Membranes Biomime´tiques et Assemblages Supramole´culaires, Institut de Chimie
et Biochimie Mole´culaires et Supramole´culaires, Universite´ Lyon 1-CNRS 5246 ICBMS, Baˆtiment CPE 43, bd du 11
novembre 1918, 69622 Villeurbanne Cedex, France
The effect of the ionic liquid 1-ethyl-3-methylimidazolium
ethylsulfate ([Emim][EtSO4]) on the copper-catalyzed
luminol chemiluminescence (CL) is reported. A drastic
light emission enhancement is observed, related to a
strong interaction between Cu2+ and the imidazolium
ring. In these conditions, the CL reaction was able to
produce light efficiently at pH as low as 6.5 (amplifica-
tion factor: Intensity+IL/Intensity-IL ) 2900). Interest-
ing effects of [Emim][EtSO4] on the enzyme glucose
oxidase activity were also evidenced, and advantages
were taken from this enhancement to perform sensitive
chemiluminescent glucose detection (LOD ) 4 µM) at
pH 8.0.
as polarized electrodes,9,10 horseradish peroxidase,11,12 cobalt,
copper, iron cations, DNAzymes,13 and the corresponding organic
complexes of these metals.14,15 The use of these catalysts usually
leads to a decrease of both the optimum reaction pH and the
necessary oxidant concentration. Enhancer could also be used in
order to obtain increased CL signal.2,12
Luminol chemiluminescent reaction catalyzed by metallic
cations is known to be optimal at alkaline pH (∼10)16 which is
compatible with few applications focused on separation methods
of luminol labeled molecules.17-19 Nevertheless, when the analyti-
cal system is based on biological molecules such as enzymes or
binding proteins, this elevated pH happens to be an insoluble
constraint and the preferred catalyst turn out to be the peroxi-
dase20 which can perform CL reaction at lower pH (∼8.5). The
consequences are the use of a fragile and expensive molecule,
instead of a cost efficient and stable metallic cation, for analytical
applications.
The catalyzed chemiluminescent (CL) reaction of luminol has
received, for more than 30 years, a great amount of attention1-6
thanks to its high sensitivity and low background signal,7,8
properties which make the reaction an attractive analytical
chemistry tool.
Luminol CL is initiated by the oxidation of luminol to luminol
radical in the presence of strong oxidants at elevated pH. These
conditions could be softened through the use of catalysts such
In the present study, we introduce the beneficial effect of
imidazolium ring-based ionic liquids (Figure 1)21 on the metal-
catalyzed luminol CL reaction, i.e., optimum pH lowering and
signal amplification.
The presence of ionic liquids (IL)22 in oxidation reaction
catalyzed by transition metals is well-known to provide significant
* To
whom
correspondence
should
be
addressed.
E-mail:
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10.1021/ac9026725 2010 American Chemical Society
Published on Web 02/17/2010
Analytical Chemistry, Vol. 82, No. 6, March 15, 2010 2401