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, Ba ˆtiment CPE 43, bd du 11 novembre 1918, 69622 Villeurbanne Cedex, France The effect of the ionic liquid 1-ethyl-3-methylimidazolium ethylsulfate ([Emim][EtSO 4 ]) on the copper-catalyzed luminol chemiluminescence (CL) is reported. A drastic light emission enhancement is observed, related to a strong interaction between Cu 2+ 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][EtSO 4 ] 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. The catalyzed chemiluminescent (CL) reaction of luminol has received, for more than 30 years, a great amount of attention 1-6 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 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- dase 20 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. 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: christophe.marquette@univ-lyon1.fr. (1) Roswell, D. F.; White, E. H. The chemiluminescence of luminol and related hydrazides. In Methods Enzymology; Fleischer, S., Fleischer, B., Eds.; Academic Press Ltd: London, 1978; Vol. 57, pp 409-423. (2) Thorpe, G. H. G.; Kricka, L. J. Enhanced chemiluminescent reactions catalysed by horseradish peroxidase. In Methods Enzymology; Fleischer, S., Fleischer, B., Eds.; Academic Press Ltd: London, 1986; Vol. 133, pp 331- 353. (3) Kricka, L. J. Anal. Chim. Acta 2003, 500, 279–286. (4) Thorpe, G. H. G.; Kricka, L. J.; Moseley, S. B.; Whitehead, T. P. Clin. Chem. 1985, 31, 1335–1341. (5) Rodrı ´guez-Lopez, J. N.; Lowe, D. J.; Herna ´ndez-Ruiz, J.; Hiner, A. N. P.; Garcı ´a-Canovas, F.; Thorneley, R. N. F. J. Am. Chem. Soc. 2001, 123, 11838–11847. (6) Lundin, A.; Hallander, L. O. B. Mechanisms of horseradish peroxidase catalysed luminol reaction in presence of various enhancers. In Biolumi- nescence and Chemiluminescence: New perspectives; Scho ¨lmerich, J., An- dreesen, R.,Kapp, A., Ernst, M., Woods, W. G., Eds.; John Wiley: Chichester, 1987; pp 555-558. (7) Tsukagoshi, K.; Nakahama, K.; Nakajima, R. Anal. Chem. 2004, 76, 4410– 4415. (8) Rose, A.; Waite, T. Anal. Chem. 2001, 73, 5909–5920. (9) Marquette, C. A.; Blum, L. J. Anal. Chim. Acta 1999, 381, 1–10. (10) Sakura, S. Anal. Chim. Acta 1992, 262, 49–57. (11) Blum, L. J., Bio-, Chemi-Luminescent Sensors. World Scientific: Singapore, 1997. (12) Marzocchi, E.; Grilli, S.; Della Ciana, L.; Prodi, L.; Mirasoli, M.; Roda, A. Anal. Biochem. 2008, 377, 189–194. (13) Chen, W.; Li, B.; Xu, C.; Wang, L. Biosens. Bioelectron. 2009, 24, 2534– 2540. (14) Uzu, T.; Sasaki, S. Org. Lett. 2007, 9, 4383–4386. (15) Burdo, T. G.; Seitz, W. R. Anal. Chem. 1975, 47, 1639–1643. (16) Badocco, D.; Pastore, P.; Favaro, G.; Macca, C. Talanta 2007, 72, 249– 255. (17) Kurihara, M.; Hasebe, T.; Kawashima, T. Bunseki Kagaku 2002, 51, 205– 233. (18) Yamaguchi, M.; Yoshida, H.; Nohta, H. J. Chromatogr., A 2002, 950, 1– 19. (19) Garcia-Campana, A. M.; Baeyens, W. R. G.; Cuadros-Rodriguez, L.; Barrero, F. A.; Bosque-Sendra, J. M.; Gamiz-Gracia, L. Curr. Org. Chem. 2002, 6, 1–20. (20) Dodeigne, C.; Thunus, L.; Lejeune, R. Talanta 2000, 51, 415–439. (21) Dupont, J. J. Braz. Chem. Soc. 2004, 15, 341–350. (22) Gordon, C. M. Appl. Catal., A 2001, 22, 101–117. Anal. Chem. 2010, 82, 2401–2404 10.1021/ac9026725  2010 American Chemical Society 2401 Analytical Chemistry, Vol. 82, No. 6, March 15, 2010 Published on Web 02/17/2010