Green electrochemiluminescence from ortho-metalated tris(2-phenylpyridine)iridium(III)

The electrochemiluminescence (ECL) of Ir(ppy)3 (ppy = 2-phenylpyridine) is reported in acetonitrile (CH3CN), mixed CH3CN/H20 (50:50 v/v), and aqueous (0.1 M KH2PO4) solutions with tri-n-propylamine as an oxidative-reductive coreactant. ECL efficiencies (phi(ecl), photons emitted per redox event) of 0.00092 in aqueous, 0.0044 in mixed, and 0.33 in CH3CN solutions for Ir(ppy)3 were obtained using Ru(bpy)3(2+) (bpy = 2,2'-bipyridine) as a relative standard (phi(ecl) = 1). Photoluminescence (PL) efficiencies of 0.039, 0.050, and 0.069 were obtained in aqueous, mixed, and acetonitrile solutions, respectively, compared to Ru(bpy)3(2+) (phi(em) = 0.042). The ECL spectra were identical to photoluminescence spectra (lambda(max) approximately equal to 517 nm), indicating formation of the same metal-to-ligand (MLCT) excited states in both ECL and PL. The ECL is linear over several orders of magnitude in mixed and acetonitrile solution with theoretical detection limits (blank plus three times the standard deviation of the noise) of 1.23 nM in CH3CN and 0.23 microM in CH3CN/ H20 (50:50 v/v).     

Electrochemiluminescence from Os(phen)2(dppene)2+ (phen = 1,10-phenanthroline and dppene = bis(diphenylphosphino)ethene)

The electrochemiluminescence (ECL) of Os(phen)2(dppene)2+ (phen = 1,10-phenanthroline and dppene = bis(diphenylphosphino)ethene) is reported in mixed CH3CN/H2O (50:50 v/v) and aqueous (0.1 M KH2PO4) solutions with tri-n-propylamine (TPrA) as an oxidative-reductive coreactant. ECL efficiencies (phi(ecl) = photons emitted/redox event) of 2.0 in aqueous, and 0.95 in mixed for Os(phen)2(dppene)2+ were obtained using Ru(bpy)3(2+) (bpy = 2,2'-bipyridine) as a relative standard (phi(ecl) = 1). Photoluminescence (PL) efficiencies of 0.094 and 0.053 were obtained in aqueous and mixed solutions, respectively, as compared to Ru(bpy)3(2+) (phi(em) = 0.042). The ECL spectra were identical to photoluminescence spectra (lambda(max) approximately 584 nm), indicating formation of the same metal-to-ligand (MLCT) excited states in both ECL and PL. The ECL is linear over several orders of magnitude in aqueous and mixed solution, with theoretical detection limits (blank plus three times the standard deviation of the noise) of 16.9 nM in H2O and 0.29 nM in CH3CN/H2O (50:50 v/v).     

Electrochemiluminescent detection of metal cations using a ruthenium(II) bipyridyl complex containing a crown ether moiety

The effects of metal ions on the electrochemiluminescence (ECL) properties of (bpy)2Ru(AZA-bpy) (bpy = 2,2'-bipyridine; AZA-bpy = 4-(N-aza-18-crown-6-methyl-2,2'-bipyridine) have been investigated. The electrochemistry, photophysics and ECL of Ru(bpy)3(2+) in the presence of Pb2+, Hg2+, Cu2+, and K+ are reported. The anodic oxidation of Ru(bpy)3(2+) produces ECL in the presence of tri-n-propylamine (TPrA) in 50:50 (v/v) CH3CN:H2O solution. Increases in ECL efficiency (photons generated per redox event) up to 20-fold that depend on both the concentration and nature of the metal ion have been observed, making this an interesting system for electrochemiluminescence metal ion sensing.     

Enhanced electrogenerated chemiluminescence in the presence of fluorinated alcohols

The electrochemistry, UV-vis absorption, photoluminescence (PL), and coreactant electrogenerated chemiluminescence (ECL) of Ru(bpy)3(2+) (where bpy=2,2'-bipyridine) have been obtained in a series of hydroxylic solvents. The solvents included fluorinated and nonfluorinated alcohols and alcohol/water mixtures. Tri-n-propylamine was used as the oxidative-reductive ECL coreactant. Blue shifts of up to 30 nm in PL emission wavelength maximums are observed compared to a Ru(bpy)3(2+)/H2O standard due to interactions of the polar excited state (i.e., *Ru(bpy)3(2+)) with the solvent media. For example, Ru(bpy)3(2+) in water has an emission maximum of 599 nm while in the more polar hexafluoropropanol and trifluoroethanol it is 562 and 571 nm, respectively. ECL spectra are similar to PL spectra, indicating the same excited state is formed in both experiments. The difference between the electrochemically reversible oxidation (Ru(bpy)3(2+/3+)) and first reduction (Ru(bpy)2(2+/1+)) correlates well with the energy gap observed in the luminescence experiments. Although the ECL is linear in all solvents with [Ru(bpy)3(2+)] ranging from 100 to 0.1 nm, little correlation between the polarity of the solvent and the ECL efficiency (phiecl=number of photons per redox event) was observed. However, dramatic increases in phiecl ranging from 6- to 270-fold were seen in mixed alcohol/water solutions.     

Electrochemiluminescence of tris(8-hydroxyquinoline-5-sulfonic acid)aluminum(III) in aqueous solution

The electrochemiluminescence (ECL) of tris(8-hydroxyquinoline-5-sulfonic acid)aluminum(III) in aqueous solution is reported. ECL is generated by complexing aluminum ions with the chelating agent 8-hydroxyquinoline-5-sulfonic acid (HQS) to form Al(HQS)3, followed by oxidation in the presence of tri-n-propylamine (TPrA). The ECL intensity peaks a potential corresponding to oxidation of both TPrA and Al(HQS)3, and the ECL emission spectrum (lambda(max) = 499 nm) matches the photoluminescence emission spectrum, indicating that the emission is from a Al(HQS)3* excited state. ECL efficiencies (phi(ecl), photons generated per redox event) of 0.002 using Ru(bpy)3(2+) (phi(ecl) = 1) as relative standard. Conditions for ECL emission were optimized and used to generate a calibration curve that was linear over the 7 x 10(-6)-4 x 10(-4) M (5-281 mg/L (ppm)) range with a theoretical limit of detection of 1 ppm. The ECL of several metal ions other than aluminum with HQS and effects on Al(HQS)3 ECL were also examined.     

The effects of nonionic surfactants on the tris(2,2'-bipyridyl)ruthenium(II)--tripropylamine electrochemiluminescence system

The electrochemistry and electrogenerated chemiluminescence (ECL) of Ru(bpy)3(2+) (bpy = 2,2'-bipyridyl) were studied in the presence of the nonionic surfactants Triton X-100, Thesit, and Nonidet P40. The anodic oxidation of Ru(bpy)3(2+) produces ECL in the presence of tri-n-propylamine in both aqueous and surfactant solutions. Increases in both ECL efficiency (> or =8-fold) and duration of the ECL signal were observed in surfactant media. A shift to lower energies of the Ru(bpy)3(2+) ECL emission by approximately 8 nm was also observed. The one-electron oxidation of Ru(bpy)3(2+) to Ru(bpy)3(3t) occurs at + 1.03 V vs Ag/AgCl in aqueous buffered (0.2 M potassium phosphate) solution as found by square wave voltammetry. This potential did not shift in surfactant systems, indicating that the redshifts in ECL emission are due to stabilization of ligand pi* orbitals in the metal-to-ligand charge-transfer excited state. These results are consistent with hydrophobic interactions between Ru(bpy)3(2+) and the nonionic surfactants.     

Quantum dot (QD)-modified carbon tape electrodes for reproducible electrochemiluminescence (ECL) emission on a paper-based platform

Stable and sensitive electrochemiluminescence (ECL) detection relies on successful immobilization of quantum dots (QDs) on working electrodes. Herein, we report a new technique to apply double-sided carbon adhesive tape as the working electrode to improve the stability and reproducibility of QD-based ECL emission. CdS QD-modified electrodes were prepared by dropping and drying CdS QD suspension on the carbon adhesive tape supported by indium tin oxide (ITO) glass. The ECL detection was performed with the prepared electrode on a paper-based platform. We tested our system using H(2)O(2) of various concentrations and demonstrated that consistent ECL emission could be obtained. We attribute stable and reproducible ECL emission to the robust attachment of CdS QDs on the carbon adhesive tape. The proposed method could be used to quantify the concentration of dopamine from 1 μM to 10 mM based on the quenching effect of dopamine on ECL emission of CdS QD system using H(2)O(2) as the coreactant. Our approach addressed the problem in the integration of stable QD-based ECL detection with portable paper-based analytical devices. The similar design offers great potential for low-cost electrochemical and ECL analytical instruments.     

Effects of poly(ethylene glycol) tert-octylphenyl ether on tris(2-phenylpyridine)iridium(III)-tripropylamine electrochemiluminescence

The effects of the nonionic surfactant Triton X-100 (poly(ethylene glycol) tert-octylphenyl ether) on the properties of tris(2-phenylpyridine)iridium(III) (Ir(ppy)3, where ppy = 2-phenylpyridine, electrochemiluminescence (ECL) have been investigated. Anodic oxidation of Ir(ppy)3 produces ECL in the presence of tri-n-propylamine (TPrA) in aqueous surfactant solution. Increases in ECL efficiency (> or = 10-fold) and TPrA oxidation current (> or = 2.0-fold) have been observed in surfactant media. The data support adsorption of surfactant on the electrode surface, thus facilitating TPrA and Ir(ppy)3 oxidation and leading to higher ECL efficiencies.     

Surfactant chain length effects on the light emission of tris(2,2'-bipyridyl)ruthenium(II)/ tripropylamine electrogenerated chemiluminescence

The effects of nonionic surfactant chain length on the properties of tris(2,2'-bipyridyl)ruthenium(II) (Ru(bpy)3(2+) where bpy = 2,2'-bipyridine) electrochemiluminescence (ECL) have been investigated. The electrochemistry, photophysics, and ECL of Ru(bpy)3(2+) in the presence of a series of nonionic surfactants are reported (Triton X-100, 114, 165, 405, 305, and 705-70). These surfactants differ in the number of poly(ethylene oxide) units incorporated into the surfactant molecule. The anodic oxidation of Ru(bpy)3(2+) produces ECL in the presence of tri-n-propylamine (TPrA) in aqueous surfactant solution. Increases in ECL efficiency (> or = 5-fold) and TPrA oxidation current (> or = 2-fold) have been observed in surfactant media. Slight decreases in ECL intensity are observed as the chain length of the nonionic surfactant increases. The data supports adsorption of surfactant on the electrode surface, thus facilitating TPrA and Ru(bpy)3(2+) oxidation and leading to higher ECL efficiencies.     

Coreactant enhanced anodic electrochemiluminescence of CdTe quantum dots at low potential for sensitive biosensing amplified by enzymatic cycle

This work used sulfite as a coreactant to enhance the anodic electrochemiluminescence (ECL) of mercaptopropionic acid modified CdTe quantum dots (QDs). This strategy proposed the first coreactant anodic ECL of QDs and led to a sensitive ECL emission of QDs in aqueous solution at relatively low potential. In the presence of dissolved oxygen, the stable ECL emission resulted from the excited QDs. Thus, an ECL detection method was proposed at +0.90 V (vs Ag/AgCl) based on the quenching of excited QDs by the analyte. Using tyrosine as a model compound, whose electrooxidized product could quench the excited QDs and thus the ECL emission, an analytical method for detection of tyrosine in a wide concentration range was developed. Furthermore, by combining an enzymatic cycle of trace tyrosinase to produce the oxidized product with an energy-transfer process, an extremely sensitive method for ECL detection of tyrosine with a subpicomolar limit of detection was developed. The sulfite-enhanced anodic ECL emission provided an alternative for traditional ECL light emitters and a new methodology for extremely sensitive ECL detection of mono- and dihydroxybenzenes at relatively low anodic potential. This strategy could be easily realized and opened new avenues for the applications of QDs in ECL biosensing.     

Inhibited Ru(bpy)3 2+ electrochemiluminescence related to electrochemical oxidation activity of inhibitors

Electrochemiluminescence (ECL) has been accepted by the analytical chemist as a powerful tool for detection of many inorganic and organic compounds. Ru(bpy)3 2+ has been the most popular ECL system, and many investigations have been focused on the application based on the enhancement or inhibition of Ru(bpy)3 2+ ECL system. However, not much attention has been paid to the theoretical investigation of this ECL system, especially to the inhibiting mechanism for the Ru(bpy)3 2+ ECL system. In the present study, many of the inorganic and organic compounds with electrochemical oxidation activity were found to strongly inhibit Ru(bpy)3 2+ ECL. To explain these inhibited ECL phenomena, a new "electrochemical oxidation inhibiting" mechanism has been proposed via the establishment of a corresponding model. The effects of applied potential, uncompensated resistance, and concentration of inhibitor on the inhibited ECL derived from the model have been verified by experiments. The new ECL inhibition mechanism can be commonly used to explain many kinds of inhibited ECL presently observed, and it is envisioned to result in finding of more inhibitors of this type and establishment of new sensitive ECL detection methods for them.     

Synthesis of ultrasmooth nanostructured diamond films by microwave plasma chemical vapor deposition using a He/H(2)/CH(4)/N(2) gas mixture

Ultrasmooth nanostructured diamond (USND) films were synthesized on Ti-6Al-4V medical grade substrates by adding helium in H(2)/CH(4)/N(2) plasma and changing the N(2)/CH(4) gas flow from 0 to 0.6. We were able to deposit diamond films as smooth as 6 nm (root-mean-square), as measured by an atomic force microscopy (AFM) scan area of 2 μm(2). Grain size was 4-5 nm at 71% He in (H(2) + He) and N(2)/CH(4) gas flow ratio of 0.4 without deteriorating the hardness (~50-60 GPa). The characterization of the films was performed with AFM, scanning electron microscopy, x-ray diffraction (XRD), Raman spectroscopy, and nanoindentation techniques. XRD and Raman results showed the nanocrystalline nature of the diamond films. The plasma species during deposition were monitored by optical emission spectroscopy. With increasing N(2)/CH(4) feedgas ratio (CH(4) was fixed) in He/H(2)/CH(4)/N(2) plasma, a substantial increase of CN radical (normalized by Balmer H(α) line) was observed along with a drop in surface roughness up to a critical N(2)/CH(4) ratio of 0.4. The CN radical concentration in the plasma was thus correlated to the formation of ultrasmooth nanostructured diamond films.     

Synthesis and photophysical studies of blue phosphorescent Ir(III) complexes with dimethylphenylphospine

New blue emitting mixed ligand iridium(III) complexes comprising one cyclometalating, two phosphines trans to each other such as Ir{(CF3)2Meppy}(PPhMe3)2(H)(L) [L = CI, NCMe, CN] [(CF3)2Meppy = 2-(3', 5'-bis-trifluoromethylphenyl)-4-methylpyridine] were synthesized and studied to tune the phosphorescence wavelength to the deep blue region and to enhance the luminescence efficiencies. To achieve deep blue emission, the trifluoromethyl group substituted on the phenyl ring and the methyl group substituted on the pyridyl ring increased HOMO-LUMO gap and achieved the hypsochromic shift. To gain insight into the factors responsible for the emission color change and the different luminescence efficiency, we investigate the electron-withdrawing capabilities of ancillary ligands using the DFT and TD-DFT calculations on the ground and excited states of the complexes. From these results, we discuss how the ancillary ligand influences the emission peak as well as the metal to ligand charge transfer (MLCT) transition efficiency. The maximum emission spectra of Ir{(CF3)2Meppy}(PPhMe3)2(H)(Cl), [Ir{(CF3),Meppy)(PPhMe3),(H)(NCMe)]+ and Ir{(CF3)2Meppy}(PPhMe3)2(H)(CN) were in the ranges of 441, 435, 434 nm, respectively.     

Electrogenerated chemiluminescence behavior of graphite-like carbon nitride and its application in selective sensing Cu2+

This paper reports for the first time the electrogenerated chemiluminescence (ECL) behavior of graphite-like carbon nitride (g-C(3)N(4)) with K(2)S(2)O(8) as the coreactant. The possible ECL reaction mechanisms are proposed. The spectral features of the ECL emission and photoluminescence (PL) of g-C(3)N(4) are compared, and their resemblance demonstrates that the excited states of g-C(3)N(4) from both ECL and photoexcitation are the same. The effects of K(2)S(2)O(8) concentration, pH, g-C(3)N(4)/carbon powder ratio, and scan rate on the ECL intensity have been studied in detail. Furthermore, it is observed that the ECL intensity is efficiently quenched by trace amounts of Cu(2+). g-C(3)N(4) is thus employed to fabricate an ECL sensor which shows high selectivity to Cu(2+) determination. The limit of detection is determined as 0.9 nM. It is anticipated that g-C(3)N(4) could be a new class of promising material for fabricating ECL sensors.     

Unique electrochemiluminescence behavior of Ru(bpy)3 in a gold/Nafion/Ru(bpy)3 composite

The unique electrochemiluminescence (ECL) behavior of tris(bipyridine) ruthenium(II) (Ru(bpy)₃²⁺) immobilized in a gold/Nafion/Ru(bpy)₃²⁺ composite material was investigated. In this composite, the Ru(bpy)₃²⁺ ECL was found mainly occurred at 0-0.4 V during the cathodic scan process and the ECL peak was at about 0.1 V, which was quite different to the reported Ru(bpy)₃²⁺ ECL. Similar to the generally observed Ru(bpy)₃²⁺ ECL, the present ECL also could be enhanced by tri-n-propylamine (TPA). It is also unique that in the presence of TPA, another ECL peak at about 0.38 V occurred. These two ECL peak potentials all could be used as characteristic potential for the ECL determination of TPA.     

Electrogenerated chemiluminescence from tris(2,2'-bipyridyl)ruthenium(II) immobilized in titania-perfluorosulfonated ionomer composite films

Electrochemical behavior and electrogenerated chemiluminescence (ECL) of tris(2,2'-bipyridyl)ruthenium(II) (Ru(bpy)3(2+)) immobilized in sol-gel-derived titania TiO2)-Nafion composite films coated on a glassy carbon electrode have been investigated. The electroactivity of Ru(bpy)3(2+) ion exchanged into the composite films and its ECL behavior were strongly dependent upon the amount of Nafion incorporated into the TiO2-Nafion composite films. The ECL sensor of Ru(bpy)32+ immobilized in a TiO2-Nafion composite with 50% Nafion content showed the maximum ECL intensities for both tripropylamine (TPA) and sodium oxalate in 0.05 M phosphate buffer solution at pH 7. Detection limits were 0.1 microM for TPA and 1.0 microM for oxalate (S/N = 3) with a linear range of 3 orders of magnitude in concentration. The present ECL sensor showed improved ECL sensitivity and long-term stability, as compared to the ECL sensors based on pure Nafion films. The present Ru(bpy)3(2+) ECL sensor based on TiO2-Nafion (50%) composite films was applied as an HPLC detector for the determination of erythromycin in human urine samples. The present Ru(bpy)3(2+) ECL sensor was stable in the mobile phase containing a high content of organic solvent (30%, v/v), in contrast to a pure Nafion-based Ru(bpy)3(2+) ECL sensor. The detection limit for erythromycin was 1.0 microM, with a linear range of 3 orders of magnitude in concentration.     

Electrochemiluminescence of luminol in alkaline solution at a paraffin-impregnated graphite electrode

The behavior of luminol electrochemiluminescence (ECL) at a paraffin-impregnated graphite electrode (PIGE) at different applied potentials was studied. Five ECL peaks were observed at 0.31, 0.59, 1.09, 1.54, and -0.58 V versus SCE, respectively, being related to potential scan direction and ranges, N2, O2, pH of the solution, and KCl concentration. The emission spectra of various ECL peaks at different potentials showed that all ECL peaks were initiated by luminol reactions. X-ray diffraction demonstrated that a simple mixture was formed between graphite and paraffin. The fluorescence spectra on the surface of the PIGE suggested that certain groups on the graphite were oxidized when the positive potential was applied to the electrode. In the presence of O2, three main ECL peaks were obtained in 0.1 mol/L KCl at pH 12.2. The ECL peak at 0.59 V with a shoulder is likely due to the reaction of luminol radicals with O2 and further electrooxidation of luminol radicals. The ECL peak at 1.54 V was suggested to be due to the electrooxidation of OH- to HO2- at higher potential and then to O2-, which reacted with luminol to produce light emission. Moreover, the oxygen-containing functional groups formed by the oxidation of the surface of the graphite electrode might enhance the ECL. At -0.58 V, the dissolved oxygen in solution was reduced to HO2-, resulting in light emission. At a potential higher than 1.64 V, ClO- was formed, leading to a broad emission wave and enhancement of the ECL peak at -0.58 V upon the reversal scan. Under nitrogen atmosphere, an ECL peak appeared at 1.09 V. At this potential, OH- was oxidized to O2, followed by the reaction with luminol to generate light emission. At pH 13.2 or 0.5 mol/L KCl, the shoulder of the ECL peak at 0.59 V became an ECL peak at 0.31 V. The conversion of luminol radicals into excited 3-aminophthalate may undergo two routes. Under these conditions, two routes might proceed at a different rate to form another ECL peak. It is concluded that luminol ECL could be readily excited by various oxygen-containing species electrogenerated at different applied potentials. Three strong ECL peaks obtained at different potentials on the PIGE might be of a potential to improve analytical selectivity and sensitivity for the detection of some analytes.     

Theoretical studies of blue phosphorescent iridium(III) complexes with phenylpyrazole and phosphines

New blue emitting mixed ligand iridium(III) complexes comprising one cyclometalating, two phosphines trans to each other such as Ir(dppz)(PPhMe2)2(H)(C1) and Ir(dppz)(PPhMe2)2(H)(CN), [dppz = 3,5-Diphenylpyrazole] were studied to tune the phosphorescence wavelength to the deep blue region and to enhance the luminescence efficiencies. To achieve deep blue emission and increase the emission efficiency, the following must occur: (1) substitution of phenyl group on the 3-position of the pyrazole ring that lower the triplet energy enough that the quenching channel is not thermally accessible, (2) changing ancillary ligands coordinated to iridium atom to phosphine and cyano groups known as very strong field ligands. Using the density functional theory (DFT) and time-dependent DFT method calculations on the ground and excited states of the complexes, we have studied how the ancillary ligand influences the emission peak as well as MLCT transition efficiency. It is showed that the strong-field ancillary ligand such as CN, PPhMe2 alters the energy gap mainly by changing the highest occupied molecular orbitals (HOMO) energy level. Their inclusion in the coordination sphere can increase the energy gap to achieve the hypsochromic shift in emission color and also lower the triplet energy level to avoid the thermal quenching.     

Effect of nonionic fluorosurfactant on the electrogenerated chemiluminescence of the tris(2,2'-bipyridine)ruthenium(II)/tri-n-propylamine system: lower oxidation potential and higher emission intensity

Fluorosurfactants are commercially available, and their applications in electrochemical systems have been the interest of many studies. Here, we describe a novel effect of a nonionic fluorosurfactant (Zonyl FSN) on the electrogenerated chemiluminescence (ECL) of the tris(2,2'-bipyridine)ruthenium(II)/tri-n-propylamine (TPrA) system at gold and platinum electrodes. Compared with its hydrocarbon analogue (Triton X-100), the adsorbed fluorosurfactant species not only rendered the electrode surfaces more hydrophobic but also significantly retarded the growth of the electrode oxide layers. As a result, more facile direct oxidation of TPrA was achieved, which led to the appearance of a low oxidation potential ECL signal (below 1.0 V vs SCE). At the gold electrode, the ECL peak appeared at 0.82 V, approximately 400 mV more negative than usual; while its intensity was approximately 50 times higher. The generation of the intense ECL signal at low oxidation potential may lead to the development of more efficient ECL analysis.     

Observing single nanoparticle collisions by electrogenerated chemiluminescence amplification

We demonstrate a novel method of observing single particle collision events with electrogenerated chemiluminescence (ECL). A single event is characterized by the enhancement of ECL intensity during the collision of an individual platinum nanoparticle (Pt NP) on an indium tin oxide electrode, which catalyzes the oxidation of Ru(bpy)3(2+) and a coreactant, for example, tri- n-propylamine (TPrA), present in the solution. Every collision produces a unique photon spike whose amplitude and frequency can be correlated with the size and concentration of the Pt NPs. A large amplification of ECL intensity can occur by choosing an appropriate measuring electrode and using high concentrations of Ru(bpy)3(2+) and the coreactant.