A ruthenium(II) complex based turn-on electrochemiluminescence probe for the detection of nitric oxide Wenzhu Zhang, a Dan Zhao, b Run Zhang, a Zhiqiang Ye, a Guilan Wang, a Jingli Yuan * a and Mei Yang * b Received 15th December 2010, Accepted 22nd February 2011 DOI: 10.1039/c0an01003k Electrochemiluminescence (ECL) detection technique using bipyridine-ruthenium(II) complexes as probes is a highly sensitive and widely used method for the detection of various biological and bioactive molecules. In this work, the spectral, electrochemical and ECL properties of a chemically modified bipyridine-ruthenium(II) complex, [Ru(bpy) 2 (dabpy)] 2+ (bpy: 2,2 0 -bipyridine; dabpy: 4-(3,4- diaminophenoxy)-2,2 0 -bipyridine), were investigated and compared with those of its nitric oxide (NO)-reaction derivative [Ru(bpy) 2 (T-bpy)] 2+ (T-bpy: 4-triazolephenoxy-2,2 0 -bipyridine) and [Ru (bpy) 3 ] 2+ . It was found that the ECL intensity of [Ru(bpy) 2 (dabpy)] 2+ could be selectively and sensitively enhanced by NO due to the formation of [Ru(bpy) 2 (T-bpy)] 2+ in the presence of tri-n-propylamine. By using [Ru(bpy) 2 (dabpy)] 2+ as a probe, a sensitive and selective ECL method with a wide linear range (0.55 to 220.0 mM) and a low detection limit (0.28 mM) was established for the detection of NO in aqueous solutions and living cells. The results demonstrated the utility and advantages of the new ECL probe for the detection of NO in complicated biological samples. 1. Introduction Nitric oxide (NO) is a ubiquitous and short-lived free radical that can be biosynthesized in animal and plant organisms. Early studies on NO only focused on its toxicity as an air pollutant. Subsequently, it was gradually recognized that a number of diseases were implicated with the NO imbalances. To date, it has been known that NO plays an important role in many funda- mental biochemical processes including blood pressure control, neurotransmission and immune response. 1–3 As an intra- and inter-cellular messenger, NO transfers signals in the cardiovas- cular and nervous systems to regulate the immune balance at low concentrations. However, at high concentration levels it can rapidly react with other reactive oxygen species (ROS) to form reactive nitrogen species (RNS) to cause the damage of the cells. 4 Therefore, the detection of NO is an attractive work for understanding the complicated functions of NO in living systems, and a number of methods, such as fluorescence, 5–10 chemiluminescence, 11 electron paramagnetic resonance spec- troscopy, 3,12–14 and electrochemiluminescence, 15 have been developed for the detection of NO. Electrochemiluminescence or electrogenerated chem- iluminescence (ECL) represents a marriage between electro- chemical and spectroscopic methods. 16 Because ECL combines the electrochemical and photoluminescent properties without any extra source of light, it can provide high sensitivity, selec- tivity, and stability over other spectroscopic detection methods. 16,17 The ECL researches on theoretical and application aspects have been rapidly developed over the past two decades. Since Tokel and Bard reported the ECL property of tris(2,2 0 - bipyridine)ruthenium(II) ([Ru(bpy) 3 ] 2+ ) in 1972, 18 this complex has become one of the most extensively investigated ECL lumi- nophores for highly sensitive immunoassay and DNA assay applications 19–26 due to its high ECL efficiency and good solu- bility in aqueous solutions. Currently, a series of derivatives of [Ru(bpy) 3 ] 2+ has been designed and synthesized for improving the light-emitting efficiency or detection selectivity. 27–33 It has been also known that different functions of Ru(II) complexes can be realized by different ligand modifications. Muegge and Richter reported that the Ru(II) complexes conjugated with crown ether moieties could be used as ECL sensors for metal ions. 34 Beer’s group demonstrated the utilities of the function- alized bipyridine-Ru(II) complexes for the ECL sensing of cations and anions. 35–37 More recently, Berni et al. described the appli- cation of a guanidinium group modified bipyridine-Ru(II) complex for the ECL detection of anions. 38 It can be considered that the bipyridine-Ru(II) complexes with suitable ligand modifications can offer more extensive ECL applications for detecting different analytes. In a previous work, we demonstrated that an o-diaminophenyl-modified bipyridine- Ru(II) complex, [Ru(bpy) 2 (dabpy)] 2+ (bpy: 2,2 0 -bipyridine; dabpy: 4-(3,4-diaminophenoxy)-2,2 0 -bipyridine), could be used as a luminescence probe for the detection of NO. 39 In this work, the spectral, electrochemical and ECL properties of [Ru a State Key Laboratory of Fine Chemicals, School of Chemistry, Dalian University of Technology, Dalian 116024, China. E-mail: jingliyuan@ yahoo.com.cn; Fax: +0086-411-84986041; Tel: +0086-411-84986041 b School of Chemistry and Chemical Engineering, Liaoning Normal University, Dalian 116029, China. E-mail: yangmeils@163.com; Fax: +0086-411-84258088; Tel: +0086-411-84258088 This journal is ª The Royal Society of Chemistry 2011 Analyst, 2011, 136, 1867–1872 | 1867 Dynamic Article Links C < Analyst Cite this: Analyst, 2011, 136, 1867 www.rsc.org/analyst PAPER