Enhanced electrochemiluminescence of Ru(bpy)32+ by flavone compounds

Flavones such as morin, rutin, quercitrin, quercetin and wogonin were found to be able to strongly enhance the electrochemiluminescence (ECL) of the Ru(bpy)₃²⁺ system. Based on this, a novel ECL method with good stability and reproducibility could be developed for determination of flavones. Under the optimum conditions, the enhanced ECL intensity was linear with the flavones concentration in a wide range. The detection limits (defined as S:N = 3) for morin, rutin, quercitrin, quercetin and wogonin were 3.2 × 10^–7 mol/L, 4.3 × 10^–7, 1.8 × 10^–7, 8.0 × 10^–8 and 1.0 × 10^–7 mol/L, respectively. In addition, the possible mechanism for the Ru(bpy)₃²⁺ ECL system in the presence of flavones is also discussed. Copyright © 2008 John Wiley & Sons, Ltd.     

Potential‐resolved electrochemiluminescence of Ru(bpy)32+/C2O42− system on gold electrode

The electrogenerated chemiluminescence of Ru(bpy)₃²⁺/C₂O₄^2? system on a pre‐polarized Au electrode was studied using a potential‐resolved electrochemiluminescence (PRECL) method. Two anodic ECL peaks were observed at 1.22 V (vs. SCE) (EP1), 1.41 V (vs. SCE) (EP2), respectively. The effects of the concentration of oxalate and Ru(bpy)₃²⁺, adsorbed sulphur, CO₂, O₂, pH of the solution and pretreatment of the Au electrode on the two PRECL peaks were examined. The surface state of the pre‐oxidized gold electrode was also studied using the X‐ray photoelectron spectroscopy (XPS) technique. Moreover, comparative studies on i–E and I–E curves were carried out and a possible mechanism involving both the catalytic and the direct electro‐oxidation pathways was proposed for the ECL of Ru(bpy)₃²⁺/C₂O₄^2? system. EP1 is attributed to the Ru(bpy)₃^2/3+ reaction catalysed by C₂O₄^2? to generate Ru(bpy)₃^2+*. EP2 is likely because C₂O₄^2? was oxidized at the electrode to form CO₂^?·, followed by reaction with Ru(bpy)₃³⁺ to generate Ru(bpy)₃^2+*. Copyright © 2002 John Wiley & Sons, Ltd.     

Flow injection analysis of tetracyclines using inhibited Ru(bpy)3(2+)/tripropylamine electrochemiluminescence system.

Tetracyclines (TCs) were found to strongly inhibit the electrochemiluminescence (ECL) from the Ru(bpy)3(2+)-tripropylamine system when a working Pt electrode was maintained at 1.05 V (vs. Ag/AgCl) in pH 8.0 carbonate buffer solution. On this basis, a flow injection (FI) procedure with inhibited electrochemiluminescence detection has been developed for the determination of tetracycline (TC) and oxytetracycline (OTC). Under the optimized condition, the linear ranges of 2.0 x 10(-8)-1.0 x 10(-5) and 1.0 x 10(-8)-1.0 x 10(-5) g/mL and the detection limits of 4.0 x 10(-9) and 3.8 x 10(-9) g/mL were obtained for TC and OTC, respectively. The relative standard deviations (RSD) were 0.68% and 1.18% for 5.0 x 10(-7) g/mL TC and OTC (n = 13), respectively. The method showed higher sensitivity than most of the reported methods. It was successfully applied to the determination of tetracycline in a Chinese proprietary medicine, Tetracyclini and Cortisone Eye Ointment, and the residues of tetracycline in honey products. The inhibition mechanism has been proposed due to an energy transfer between electrogenerated Ru(bpy)3(2+)* and benzoquinone derivatives at the electrode surface.     

Electrochemiluminescence detection of methamphetamine based on a Ru(bpy)32+‐doped silica nanoparticles/Nafion composite film modified electrode

An electrochemiluminescence (ECL) approach for methamphetamine determination was developed based on a glassy carbon electrode modified with a Ru(bpy)₃²⁺‐doped silica nanoparticles/Nafion composite film. The monodispersed nanoparticles, which were about 50 nm in size, were synthesized using the water‐in‐oil microemulsion method. The ECL results revealed that Ru(bpy)₃²⁺ doped in silica nanoparticles retained its original photo‐ and electrochemical properties. The ECL intensity was found to be proportional to methamphetamine concentration over the range from 1.0 × 10^?7 to 1.0 × 10^?5 mol L^?1, and the detection limit was found to be 2.6 × 10^?8 mol L^?1. The proposed ECL approach was used to analyze the methamphetamine content in drugs. Copyright © 2009 John Wiley & Sons, Ltd.     

Exploring the electrochemiluminescent behavior of procaterol hydrochloride in the presence of Ru(bpy)32+ and its analytical application in pharmaceutical preparation

Based on the strong enhancement effect of procaterol hydrochloride on the electrochemiluminescence (ECL) of Ru(bpy)₃²⁺ (bpy = 2,2′‐bipyridine) in an alkaline H₃PO₄–NaOH buffer solution on a bare Pt electrode, a simple, rapid and sensitive method was developed for the determination of procaterol hydrochloride. The optimum conditions for the enhanced ECL have been developed in detail in this work. Under optimum conditions, the logarithmic ECL enhancement vs. the logarithmic concentration of procaterol hydrochloride is linear over a wide concentration range of 2.0 × 10^?7 to 2.0 × 10^?4 M (r =  0.9976), with a limit of detection of 1.1 × 10^?8 M (S/N =  3), and a relative standard deviation of 2.1% (n =  7, c =  5.0 × 10^?6 M). The proposed method was applied to the determination of this drug in tablets with recoveries of 89.7%–98.5%. In addition, a possible mechanism for the enhanced ECL of Ru(bpy)₃²⁺, which is caused by ProH, has also been proposed.     

Electrochemiluminescence determination of codeine or morphine with an organically modified silicate film immobilizing Ru(bpy)3(2+).

An ECL approach was developed for the determination of codeine or morphine based on tris(2,2'-bipyridine)ruthenium(II) (Ru(bpy)(3)(2+)) immobilized in organically modified silicates (ORMOSILs). Tetramethoxysilane (TMOS) and dimethyldimethoxysilane (DiMe-DiMOS) were selected as co-precursors for ORMOSILs, which were then immobilized on a surface of glassy carbon electrode (GCE) by a dip-coating process. Ru(bpy)(3)(2+) was immobilized in the ORMOSIL film via ion-association with poly(p-styrenesulphonate). The ORMOSIL-modified GCE presented good electrochemical and photochemical activities. In a flow system, the eluted codeine or morphine was oxidized on the modified GCE and reacted with immobilized Ru(bpy)(3)(2+) at a potential of +1.20 V (vs. Ag/AgCl). The modified electrode was used for the ECL determination of codeine or morphine and showed high sensitivity. The calibration curves were linear in the range 2 x 10(-8)-5 x 10(-5) mol/L for codeine and 1 x 10(-7)-3 x 10(-4) mol/L for morphine. The detection limit was 5 x 10(-9) mol/L for codeine and 3 x 10(-8) mol/L for morphine, at signal:noise ratio (S:N)=3. Both codeine and morphine showed reproducibility with RSD values <2.5% at 1.0 x 10(-6) mol/L. Furthermore, the modified electrode immobilized Ru(bpy)(3)(2+) was applied to the ECL determination of codeine or morphine in incitant samples.     

Highly sensitive electrochemiluminescence determination of etamsylate using a low‐cost electrochemical flow‐through cell based on a tris(2, 2'‐bipyridyl)ruthenium(II)–Nafion‐modified carbon paste electrode

A simple and sensitive electrochemiluminescence (ECL) method for the determination of etamsylate has been developed by coupling an electrochemical flow‐through cell with a tris(2,2'‐bipyridyl)ruthenium(II) (Ru(bpy)₃²⁺)–Nafion‐modified carbon electrode. It is based on the oxidized Ru(bpy)₃²⁺ on the electrode surface reacting with etamsylate and producing an excellent ECL signal. Under optimized experimental conditions, the proposed method allows the measurement of etamsylate over the range of 8–1000 ng/mL with a correlation coefficient of r = 0.9997 (n = 7) and a limit of detection of 1.57 ng/mL (3σ), the relative standard deviation (RSD) for 1000 ng/mL etamsylate (n = 7) is 0.96%. The immobilized Ru(bpy)₃²⁺ carbon paste electrode shows good electrochemical and photochemical stability. This method is rapid, simple, sensitive and has good reproducibility. It has been successfully applied to the determination of the studied etamsylate in pharmaceutical preparations with satisfactory results. The possible ECL reaction mechanism has also been discussed. Copyright © 2013 John Wiley & Sons, Ltd.     

Electrochemiluminescence of an electrocatalytic action of etimicin on Tris(2,2′‐bipyridyl)ruthenium(II) immobilized in Nafion modified carbon paste electrode

A sensitive electrochemiluminescence (ECL) detection of etimicin at Tris(2,2′‐bipyridyl)ruthenium(II) [Ru(bpy)₃²⁺]–Nafion modified carbon paste electrodes was developed. The immobilized Ru(bpy)₃²⁺ shows good electrochemical and photochemical activities. Electrochemical and electrochemiluminescence characterizations of the modified carbon electrodes were made by means of cyclic voltammetry and electrochemical impendence spectroscopy. The modified electrode showed an electrocatalytic response to the oxidation of etimicin, producing a sensitized ECL signal. The ECL sensor showed a linear response to etimicin in the range of 8.0–160.0 ng mL^?1 with a detection limit of 6.7 ng mL^?1. This method for etimicin determination possessed good sensitivity and reproducibility with a coefficient of variation of 5.1% (n = 7) at 100 ng mL^?1. The ECL sensor showed good selectivity and long‐term stability. Its surface could be renewed quickly and reproducibly by a simple polish step. Copyright © 2009 John Wiley & Sons, Ltd.     

Flow injection analysis of thiamazole based on strong Ru(bpy)32+ co‐reactant electrochemiluminescence

Based on the strong electrochemiluminescence (ECL) reaction between thiamazole and tris(2,2′‐bipyridine)ruthenium(II) (Ru(bpy)₃²⁺), a sensitive, simple and rapid flow injection analysis method for the determination of thiamazole was developed. When a Pt working electrode was maintained at a potential of +1.50 V (vs Ag/AgCl) in pH 12.0 H₃PO₄–NaOH solution containing thiamazole and Ru(bpy)₃²⁺ at a flow rate of 1.0 mL/min, a linear range of 2.0 × 10⁻⁷–1.0 × 10⁻⁴ mol/L with a detection limit of 5.0 × 10⁻⁸ mol/L was obtained for the detection of thiamazole. The method showed good reproducibility with a relative standard deviation (RSD) of 0.75%. The method has been successfully applied to the determination of thiamazole in spiked animal feeds. In addition, a co‐reactant ECL mechanism was proposed for the thiamazole–Ru(bpy)₃²⁺ system. Copyright © 2014 John Wiley & Sons, Ltd.     

Self‐quenching in the electrochemiluminescence of Ru(bpy)32+ using ascorbic acid as co‐reactant

In this study, electrochemiluminescence (ECL) of Ru(bpy)₃²⁺ (bpy = 2,2′‐bipyridyl) using ascorbic acid (H₂A) as co‐reactant was investigated in an aqueous solution. When H₂A was co‐existent in a Ru(bpy)₃²⁺‐containing buffer solution, ECL peaks were observed at a potential corresponding to the oxidation of Ru(bpy)₃²⁺, and the intensity was proportional to H₂A concentration at lower concentration levels. The formation of the excited state *Ru(bpy)₃²⁺ was confirmed to result from the co‐reaction between Ru(bpy)₃³⁺and the intermediate of ascorbate anion radical (A⁻•), which showed the maximum ECL at pH = 8.8. It is our first finding that the ECL intensity would be quenched significantly when the concentration of H₂A was relatively higher, or upon ultrasonic irradiation. In most instances, quenching is observed with four‐fold excess of H₂A over Ru(bpy)₃²⁺. The diffusional self‐quenching scheme as well as the possible reaction pathways involved in the Ru(bpy)₃²⁺–H₂A ECL system are discussed in this study. Copyright © 2008 John Wiley & Sons, Ltd.     

Cathodic electrochemiluminescence of acetonitrile, acetonitrile-1,10-phenanthroline and acetonitrile-ternary Eu(III) complexes at a gold electrode.

Cathodic electrochemiluminescence (ECL) behaviours of the acetonitrile, acetonitrile-1,10-phenanthroline (phen) and acetonitrile-ternary Eu(III) complex systems at a gold electrode were studied. One very weak cathodic ECL-2 at -3.5 V was observed in 0.1 mol/L tetrabutylammonium tetrafluoroborate (TBABF(4)) acetonitrile solution. When 10 mmol/L tetrabutylammonium peroxydisulphate [(TBA)(2)S(2)O(8)] was added to 0.1 mol/L TBABF(4) acetonitrile solution, another cathodic ECL-1 at -2.7 V appeared and the potential for ECL-2 was shifted from -3.5 to -3.1 V. Furthermore, ECL-2 intensity was enhanced about 20-fold. When 1 x 10(-4) mol/L phen was added to 0.1 mol/L TBABF(4) + 10 mmol/L (TBA)(2)S(2)O(8) acetonitrile solution, the ECL intensities of ECL-1 and ECL-2 were enhanced about 20-fold compared with those of 0.1 mol/L TBABF(4) + 10 mmol/L (TBA)(2)S(2)O(8) acetonitrile solution. The maximum emission peaks of ECL-1 and ECL-2 in the three systems mentioned above appeared at about 530 nm. The products obtained by electrolysing 0.1 mol/L TBABF(4) acetonitrile solution at -3.5 V for 20 min were analysed by Fourier Transform Infrared (FTIR) spectra and gas chromatography-mass spectrometry (GC-MS) and the emitter of ECL-1 and ECL-2 was identified as excited state polyacetonitrile. When ternary Eu(III) complexes were presented in 0.1 mol/L TBABF(4) + 10 mmol/L (TBA)(2)S(2)O(8) acetonitrile solution, another maximum emission peak with a narrow band centred at about 610 nm appeared in ECL-1 in addition to the maximum emission peaks at about 530 nm for ECL-1 and ECL-2. The emitter of ECL emission at 610 nm was identified as the excited states Eu(III)*. The mechanisms for cathodic ECL behaviours of the acetonitrile, acetonitrile-phen and acetonitrile-ternary Eu(III) complex systems at a gold electrode have been proposed. The extremely sharp emission bands for ternary Eu(III) complexes may have analytical potential.     

Flow‐injection chemiluminescence determination of ofloxacin using the Ru(bpy)2(CIP)2+−Ce(IV) system and its application

This paper reports a flow‐injection chemiluminescence method for the determination of ofloxacin (OFLX) using the Ru(bpy)₂(CIP)²⁺–Ce(IV) system. Under the optimum conditions, the relative CL intensity was proportional to the concentration of OFLX in the range 3.0 × 10^–8–1.0 × 10^–5 mol/L and the detection limit was 4.2 × 10^–9 mol/L. The proposed method has been successfully applied to the determination of ofloxacin in pharmaceuticals and human urine. The chemiluminescence mechanism of the system is also discussed. Copyright © 2008 John Wiley & Sons, Ltd.     

An amperometric lactate biosensor based on lactate dehydrogenase immobilized onto graphene oxide nanoparticles‐modified pencil graphite electrode

A novel amperometric lactate biosensor was developed based on immobilization of lactate dehydrogenase onto graphene oxide nanoparticles‐decorated pencil graphite electrode. The enzyme electrode was characterized by scanning electron microscopy, Fourier transform infrared spectroscopy (FTIR), and cyclic voltammetry at different stages of its construction. The biosensor showed optimum response within 5 s at pH 7.3 (0.1 M sodium phosphate buffer) and 35°C, when operated at 0.7 V. The biosensor exhibited excellent sensitivity (detection limit as low as 0.1 μM), fast response time (5 s), and wider linear range (5–50 mM). Analytical recovery of added lactic acid in serum was between 95.81–97.87% and within‐batch and between‐batch coefficients of variation were 5.04 and 5.40%, respectively. There was a good correlation between serum lactate values obtained by standard colorimetric method and the present biosensor (r = 0.99). The biosensor measured lactate levels in sera of apparently healthy subjects and persons suffering from lactate acidosis and other biological materials (milk, curd, yogurt, beer, white wine, and red wine). The enzyme electrode lost 25% of its initial activity after 60 days of its regular uses, when stored dry at 4°C.     

Capillary electrophoresis coupled with end‐column electrochemiluminescence for the determination of ephedrine in human urine,and a study of its interactions with three proteins

A tris(2,2‐bipyridyl)ruthenium(II) (Ru(bpy)₃²⁺)‐based electrochemiluminescence (ECL) detection coupled with capillary electrophoresis (CE) method has been established for the sensitive determination of ephedrine for the first time. Under the optimized conditions [ECL detection at 1.15 V, 25 mmol/L phosphate buffer solution (PBS), pH 8.0, as running buffer, separation voltage 12.5 kV, 5 mmol/L Ru(bpy)₃²⁺ with 60 mmol/L PBS, pH 8.5, in the detection cell] linear correlation (r = 0.9987) between ECL intensity and ephedrine concentration was obtained in the range 6.0 × 10^–8–6.0 × 10^–6 g/mL. The detection limit was 4.5 × 10^–9 g/mL (S:N = 3). The developed method was successfully applied to the analysis of ephedrine in human urine and the investigation of its interactions with three proteins, including bovine serum albumin (BSA), cytochrome C (Cyt‐C) and myoglobin (Mb). The number of binding sites and the binding constants between ephedrine and BSA, Cyt‐C and Mb were 8.52, 12.60, 10.66 and 1.55 × 10⁴ mol/L, 6.58 × 10³ mol/L and 1.59 × 10⁴ mol/L, respectively. Copyright © 2011 John Wiley & Sons, Ltd.     

Flow‐injection method for the determination of iodide/iodine using Ru(bpy)33+–NADH chemiluminescence detection

A two‐channel flow‐injection (FI) method is reported for the determination of iodide and iodine by its enhancement effect on the Ru(bpy)₃³⁺–NADH chemiluminescence (CL) system. The limit of detection (3 s of blank) was 1.0 × 10^–9 mol/L iodide/iodine, with a sample throughput of 60/h. The calibration graphs over the range 1.0–50 × 10^–8 mol/L gave correlation coefficients of 0.9994 and 0.999 (n = 5) with relative standard deviations (RSD; n = 4) of 1.0–2.5%, respectively. The effects of interfering cations, anions and some organic compounds were also studied. The method was applied to iodized salts and pharmaceutical samples and the results obtained were in good agreement with the value quoted. The CL method developed was compared with spectrophotometric method. Copyright © 2008 John Wiley & Sons, Ltd.     

Long‐lived electrochemiluminescence of ruthenium (II) complexes/tri‐n‐propylamine in aqueous solutions

Although the clinical use of immunoassays based on the oxidative‐reduction electrochemiluminescence (ECL) of tris(2,2′‐bipyridine)ruthenium (II)/tri‐n‐propylamine has been a great success, elucidation of the ECL generation mechanism still remains unsatisfactory. We report here our experimental observations of long‐lived luminescence that remains detectable for several seconds after termination of electrochemical heterogeneous oxidation. Long‐lived luminescence was observed in both a surfactant‐free buffer and a surfactant‐containing broadly used commercial buffer under different conditions. The slow decay of emission seems to have been unnoticed in previous ECL mechanistic studies. Within the frame of the reaction schemes so far proposed, its origin is inconclusively ascribed to the reductive‐oxidation process of ruthenium (II) complex, that is Ru(bpy)₃²⁺ → Ru(bpy)₃¹⁺ → Ru(bpy)₃²⁺* → Ru(bpy)₃²⁺ with the involvement of the tri‐n‐propylamine‐derived radical cation. It is anticipated that long‐lived ECL will suggest a research approach to separate some homogeneous reactions from the complicated reaction system and therefore help to resolve the mechanistic mystery.     

Determination of bergenin based on the electrochemiluminescence quenching of tris(2,2′‐bipyridine)‐ruthenium(II)

Quenching effects of bergenin, based on the electrochemiluminescence (ECL) of the tris(2,2′‐bipyridyl)‐ruthenium(II) (Ru(bpy)₃²⁺)/tri‐n‐propylamine (TPrA) system in aqueous solution, is been described. The quenching behavior can be observed with a 100‐fold excess of bergenin over Ru(bpy)₃²⁺. In the presence of 0.1 m TPrA, the Stern–Volmer constant (K_SV) of the ECL quenching is as high as 1.16 × 10⁴ M^?1 for bergenin. The logarithmic plot of the inhibited ECL versus logarithmic plot of the concentration of bergenin was linear over the range 3.0 × 10^?6–1.0 × 10^?4 mol/L. The corresponding limit of detection was 6.0 × 10^?7 mol/L for bergenin (S/N = 3). In the mechanism of quenching it is believed that the competition of the active free radicals between Ru(bpy)₃²⁺/TPrA and bergenin was the key factor for the ECL inhibition of the system. Photoluminescence, cyclic voltammetry, coupled with bulk electrolysis, supports the supposition mechanism of the Ru(bpy)₃²⁺/TPrA–bergenin system. Copyright © 2015 John Wiley & Sons, Ltd.     

Large enhancement of oscillating chemiluminescence with [Ru(bpy)3]2+‐catalyzed Belousov–Zhabotinsky reaction in the presence of tri‐n‐propylamine

Oscillating chemiluminescence enhanced by the addition of tri‐n‐propylamine (TPrA) to the typical Belousov–Zhabotinsky (BZ) reaction system catalyzed by ruthenium(II)tris(2.2'‐bipyridine)(Ru(bpy)₃²⁺) was investigated using a luminometry method. The [Ru(bpy)₃]²⁺/TPrA system was first used as the catalyst for a BZ oscillator in a closed system, which exhibited a shorter induction period, higher amplitude and much more stable chemiluminescence (CL) oscillation. The effects of various concentrations of TPrA, oxygen and nitrogen flow rate on the oscillating behavior of this system were examined. In addition, the CL intensity of the [Ru(bpy)₃]²⁺/TPrA–BZ system was found to be inhibited by phenol, thus providing a way for use of the BZ system in the determination of phenolic compounds. Moreover, the possible mechanism of the oscillating CL reaction catalyzed by [Ru(bpy)₃]²⁺/TPrA and the inhibition effects of oxygen and phenol on this oscillating CL system were considered. Copyright © 2012 John Wiley & Sons, Ltd.     

Electrogenerated chemiluminescence of luminol in neutral and alkaline aqueous solutions on a silver nanoparticle self-assembled gold electrode.

The electrochemiluminescence (ECL) behaviour of luminol on a silver nanoparticle self-assembled gold electrode in neutral and alkaline solutions was investigated using conventional cyclic voltammetry (CV). The silver nanoparticle self-assembled gold electrode exhibited excellent ECL properties for the luminol ECL system. In neutral solutions, four ECL peaks (ECL-1-ECL-4) were observed at 0.73, 1.15, -0.46 and -1.35 V (vs. SCE), respectively. The intensities of these peaks were enhanced significantly compared with those on a bulk gold electrode and a gold nanoparticle self-assembled gold electrode. It was found that ECL-1 and ECL-2 on a silver nanoparticle-modified electrode were about 1000 and 1770 times stronger than those on a bare Au electrode and were about 17 and 15 times stronger than those on a gold nanoparticle-modified electrode, respectively. In alkaline solutions, four ECL peaks were also observed that were much stronger than those in neutral solutions, and ECL-1 and ECL-2 were enhanced by about three orders and one order of magnitude compared with those on a bare Au electrode and on a gold nanoparticle self-assembled electrode, respectively. Moreover, the silver nanoparticle-modified electrode exhibited good stability and reproducibility for luminol ECL. These peaks were found to depend on a number of factors, including silver nanoparticles on the surface of the modified electrode, potential scan direction, scan rate, scan range, the presence of O2 or N2, pH values, the concentrations of NaBr and luminol, and buffer solutions. The emitter of the ECL was confirmed as 3-aminophthalate by analysing the CL spectra. The surface state of the silver nanoparticle self-assembled electrode was characterized by scanning electron microscopy (SEM) and the interface property of the electrode was studied by electrochemical impedance spectroscopy (EIS). A mechanism for the formation of these ECL peaks is proposed. The results demonstrate that luminol has excellent ECL properties, such as strong ECL intensity and good reproducibility on a silver nanoparticle-modified gold electrode, in both neutral and alkaline solutions, which is of great potential in analytical applications.     

Experimental and DFT studies on the DNA-binding trend and spectral properties of complexes [Ru(bpy)2L] (L = dmdpq, dpq, and dcdpq)

The trend in DNA-binding affinities and the spectral properties of a series of Ru(II) polypyridyl complexes, [Ru(bpy)₂(dmdpq)]²⁺ (1), [Ru(bpy)₂(dpq)]²⁺ (2), [Ru(bpy)₂(cndpq)]²⁺ (3) (bpy = 2,2′-bipyridine; dpq = dipyrido[3,2-d:2′,3′-f]quinoxaline; dmdpq = di-methyl-dpq; dcdpq = di-cyano-dpq), have been experimentally and theoretically investigated. The DNA-binding constants K_b of the complexes were determined systematically with spectrophotometric titration. The density functional theory (DFT) and time-dependent DFT (TDDFT) calculations were carried out for these complexes. The experimental results show that these complexes bind to DNA in intercalation mode, and the order of their intrinsic DNA-binding constants K_b is K_b(1) < K_b(2) ? K_b(3). The substituents on the intercalative ligands of the complexes play a very important role in the control of DNA-binding affinities of the complexes, in particular, the stronger electron-withdrawing substituent (-CN) on the intercalative ligand can greatly improve the DNA-binding property of the derivative complex. The trend in DNA-binding affinities as well as the spectral properties of metal-ligand charge-transition (¹MLCT) of this series of complexes can be reasonably explained by applying the DFT and TDDFT calculations and the frontier molecular orbital theory.