Electrochemiluminescent peptide nucleic acid-like monomers containing Ru(II)-dipyridoquinoxaline and Ru(II)-dipyridophenazine complexes

A series of Ru(II)-peptide nucleic acid (PNA)-like monomers, [Ru(bpy)(2)(dpq-L-PNA-OH)](2+) (M1), [Ru(phen)(2)(dpq-L-PNA-OH)](2+) (M2), [Ru(bpy)(2)(dppz-L-PNA-OH)](2+) (M3), and [Ru(phen)(2)(dppz-L-PNA-OH)](2+) (M4) (bpy = 2,2'-bipyridine, phen = 1,10-phenanthroline, dpq-L-PNA-OH = 2-(N-(2-(((9H-fluoren-9-yl)methoxy)carbonylamino)ethyl)-6-(dipyrido[3,2-a:2',3'-c]phenazine-11-carboxamido)hexanamido)acetic acid, dppz-L-PNA-OH = 2-(N-(2-(((9H-fluoren-9-yl) methoxy)carbonylamino)ethyl)-6-(dipyrido[3,2-f:2',3'-h]quinoxaline-2-carboxamido)acetic acid) have been synthesized and characterized by IR and (1)H NMR spectroscopy, mass spectrometry, and elemental analysis. As is typical for Ru(II)-tris(diimine) complexes, acetonitrile solutions of these complexes (M1-M4) show MLCT transitions in the 443-455 nm region and emission maxima at 618, 613, 658, and 660 nm, respectively, upon photoexcitation at 450 nm. Changes in the ligand environment around the Ru(II) center are reflected in the luminescence and electrochemical response obtained from these monomers. The emission intensity and quantum yield for M1 and M2 were found to be higher than for M3 and M4. Electrochemical studies in acetonitrile show the Ru(II)-PNA monomers to undergo a one-electron redox process associated with Ru(II) to Ru(III) oxidation. A positive shift was observed in the reversible redox potentials for M1-M4 (962, 951, 936, and 938 mV, respectively, vs Fc(0/+) (Fc = ferrocene)) in comparison with [Ru(bpy)(3)](2+) (888 mV vs Fc(0/+)). The ability of the Ru(II)-PNA monomers to generate electrochemiluminescence (ECL) was assessed in acetonitrile solutions containing tripropylamine (TPA) as a coreactant. Intense ECL signals were observed with emission maxima for M1-M4 at 622, 616, 673, and 675 nm, respectively. At an applied potential sufficiently positive to oxidize the ruthenium center, the integrated intensity for ECL from the PNA monomers was found to vary in the order M1 (62%) > M3 (60%) > M4 (46%) > M2 (44%) with respect to [Ru(bpy)(3)](2+) (100%). These findings indicate that such Ru(II)-PNA bioconjugates could be investigated as multimodal labels for biosensing applications.

Analyte-induced formation of partial duplexes for the preparation of a label-free electrochemiluminescent aptasensor

Analyte-induced formation of partial duplexes was used for biosensor development with cocaine as a model. The cocaine-aptamer interaction resulted in formation of a partial double strand section in the aptamer, where Ru(phen)(3)(2+) was intercalated for electrochemiluminescent analysis of cocaine.

Electrochemiluminescence of tris(2,2'-bipyridyl)ruthenium and its applications in bioanalysis: a review

Electrochemiluminescence (ECL) of tris(2,2'-bipyridyl)ruthenium(II) [Ru(bpy)(3) (2+)] is an active research area and includes the synthesis of ECL-active materials, mechanistic studies and broad applications. Extensive research has been focused on this area, due to its scientific and practical importance. In this mini-review we focus on the bio-related applications of ECL. After a brief introduction to Ru(bpy)(3) (2+) ECL and its mechanisms, its application in constructing an effective bioassay is discussed in detail. Three types of ECL assay are covered: DNA, immunoassay and functional nucleic acid sensors. Finally, future directions for these assays are discussed.

Sensitive and isothermal electrochemiluminescence gene-sensing of Listeria monocytogenes with hyperbranching rolling circle amplification technology

Listeria monocytogenes (L. monocytogenes) is one of the most problematic human pathogens, as it is mainly transmitted through the food chain and cause listeriosis. Thus, specific and sensitive detection of L. monocytogenes is required to ensure food safety. In this study, we proposed a method using hyperbranching rolling circle amplification (HRCA) combined with magnetic beads based electrochemiluminescence (ECL) to offer an isothermal, highly sensitive and specific assay for the detection of L. monocytogenes. At first, a linear padlock probe was designed to target a specific sequence in the hly gene which is specific to L. monocytogenes and then ligated by Taq DNA ligase. After ligation and digestion, further amplification by HRCA with a biotiny labeled primer and a tris (bipyridine) ruthenium (TBR) labeled primer was performed. The resulting HRCA products were then captured onto streptavidin-coated paramagnetic beads and were analyzed by magnetic beads based ECL platform to confirm the presence of targets. Through this approach, as low as 10 aM synthetic hly gene targets and about 0.0002 ng/μl of genomic DNA from L. monocytogenes can be detected, the ability to detect at such ultratrace levels could be attributed to the powerful amplification of HRCA and the high sensitivity of current magnetic bead based ECL detection platform.

A sensitive, non-damaging electrochemiluminescent aptasensor via a low potential approach at DNA-modified gold electrodes

Electrochemiluminescence (ECL)-based biosensors are often used in the field of DNA- and protein-assay. Although ruthenium complex-based ECL is sensitive, its high exciting potential may lead to oxidation damage to biomolecules. For the first time, a non-damaging, low potential ECL aptasensor was constructed for bioassay with lysozyme as a model. After a single-stranded anti-lysozyme aptamer was attached to a gold electrode, a double stranded (ds)-DNA formed with its complementary strand. Ru(phen)(3)(2+), as an ECL probe, was intercalated into the ds-DNA. The hybridization of lysozyme with its aptamer led to the dissociation of ds-DNA because of the high stability of the aptamer-lysozyme and therefore the Ru(phen)(3)(2+) intercalated into ds-DNA was released. A low potential ECL was observed at the ds-DNA-modified electrode because ds-DNA was able to preconcentrate tripropylamine (TPA) and acted as the acceptor of the protons released from protonated TPAH(+). While the DNA sequence (anti-lysozyme aptamer) was used as the special recognition element for lysozyme, the formed ds-DNA also provided a micro-environment for low potential ECL. The low potential ECL aptasensor achieved the determination of lysozyme with a detection limit of 0.45 pM. The day-to-day precision (RSDs, n = 5) for the determination of lysozyme was lower than 5%, showing the reliability of the aptasensor. The regeneration of the aptasensor confirmed that the low potential for ECL could decrease oxidation damage to biomolecules. Further, the proposed method was successfully used to analyze diluted egg white sample directly. The protocol exhibited a promising platform for sensitive bioassay and could be further applied for the development of other low potential ECL sensing systems.

Determination of isocyanates by capillary electrophoresis with tris(2,2'-bipyridine)ruthenium(II) electrochemiluminescence

CE with tris(2,2'-bipyridyl) ruthenium(II) (Ru(bpy)(3) (2+)) electrochemiluminescence (ECL) detection for the quantitative determination of isocyanates was first reported. Hexamethylene diisocyanate (HDI) and hexyl isocyanate (HI) were used as the model analytes. Commercially available N,N-diethyl-N'-methylethylenediamine was used as the derivatization reagent. It has both a secondary amine group and a tertiary amine group. The secondary amine group can quantitatively react with isocyanate group, and the tertiary amine group can react with Ru(bpy)(3) (2+) to produce strong ECL signal for sensitive detection. The derivatization reaction was almost instantaneous and is much faster than other reported derivative reactions using other derivative reagents. The urea formed was stable. Linear calibration curve was obtained in the range from 0.01 to 10 microM for HDI, and 0.02 to 20 microM for hexyl isocyanate (HI). The detection limit is 0.01 microM for HDI and 0.02 microM for HI. The method is more sensitive than UV-detection and electrochemical detection. For practical application, recovery higher than 90% for HDI and HI was obtained for foam sample.

Novel poly-dopamine adhesive for a halloysite nanotube-Ru(bpy)(3)2+ electrochemiluminescent sensor

Herein, for the first time, the electrochemiluminescent sensor based on Ru(bpy)₃²⁺-modified electrode using dopamine as an adhesive was successfully developed. After halloysite nanotube slurry was cast on a glassy carbon electrode and dried, an alkaline dopamine solution was added on the electrode surface. Initially, polydopamine belts with dimensions of tens to hundreds of nanometers formed via oxidization of the dopamine by ambient oxygen. As the incubation time increased, the nanobelts became broader and then united with each other to form a polydopamine film. The halloysite nanotubes were embedded within the polydopamine film. The above electrode was soaked in Ru(bpy)₃²⁺ aqueous solution to adsorb Ru(bpy)₃²⁺ into the active sites of the halloysite nanotubes via cation-exchange procedure. Through this simple procedure, a Ru(bpy)₃²⁺-modified electrode was obtained using only 6.25 µg Ru(bpy)₃²⁺, 15.0 µg dopamine, and 9.0 µg halloysite nanotubes. The electrochemistry and electrochemiluminescence (ECL) of the modified electrode was investigated using tripropylamine (TPA) and nitrilotriacetic acid (NTA) as co-reactants. The different ECL behaviors of the modified electrode using NTA and TPA as well as the contact angle measurements reflected the hydrophilic character of the electrode. The results indicate that halloysite nanotubes have a high loading capacity for Ru(bpy)₃²⁺ and that dopamine is suitable for the preparation of modified electrodes.

Applications of nanomaterials in electrogenerated chemiluminescence biosensors

Electrogenerated chemiluminescence (also called electrochemiluminescence and abbreviated ECL) involves the generation of species at electrode surfaces that then undergo electron-transfer reactions to form excited states that emit light. ECL biosensor, combining advantages offered by the selectivity of the biological recognition elements and the sensitivity of ECL technique, is a powerful device for ultrasensitive biomolecule detection and quantification. Nanomaterials are of considerable interest in the biosensor field owing to their unique physical and chemical properties, which have led to novel biosensors that have exhibited high sensitivity and stability. Nanomaterials including nanoparticles and nanotubes, prepared from metals, semiconductor, carbon or polymeric species, have been widely investigated for their ability to enhance the efficiencies of ECL biosensors, such as taking as modification electrode materials, or as carrier of ECL labels and ECL-emitting species. Particularly useful application of nanomaterials in ECL biosensors with emphasis on the years 2004-2008 is reviewed. Remarks on application of nanomaterials in ECL biosensors are also surveyed.

Electrogenerated chemiluminescence

In electrogenerated chemiluminescence, also known as electrochemiluminescence (ECL), electrochemically generated intermediates undergo a highly exergonic reaction to produce an electronically excited state that then emits light. These electron-transfer reactions are sufficiently exergonic to allow the excited states of luminophores, including polycyclic aromatic hydrocarbons and metal complexes, to be created without photoexcitation. For example, oxidation of [Ru(bpy)(3)](2+) in the presence of tripropylamine results in light emission that is analogous to the emission produced by photoexcitation. This review highlights some of the most exciting recent developments in this field, including novel ECL-generating transition metal complexes, especially ruthenium and osmium polypyridine systems; ECL-generating monolayers and thin films; the use of nanomaterials; and analytical, especially clinical, applications.

Electrochemistry and electrochemiluminescence of [Ru(II)-tris(bathophenanthroline-disulfonate)]4- in aprotic conditions and aqueous buffers

In this work, the electrochemical and ECL properties of tris[1,10-phenanthrolinediyl-4,7-di(benzenesulfonate)]Ru(II) ([Ru(BPS)3]4-) have been addressed in both strictly aprotic conditions and aqueous buffers. A combined theoretical and experimental approach is presented to focus thermodynamics and kinetic effects of electro-generated species possessing highly negative charge. The complex, prepared as the sodium salt by using a newly developed procedure, was subsequently converted to the tetrabutylammonium salt by ion exchange, thus making it soluble in organic media and allowing, for the first time, its thorough electrochemical investigation in ultra-dry aprotic media. The electrochemically induced luminescence (ECL) of Na 4[Ru(BPS)3] in phosphate buffer, using the co-reactant method (tripropylamine), was investigated as a function of the electrode material and halide addition, and ECL intensities six times higher than that of [Ru(bpy)3]2+ were found. In addition, the ECL behavior of this promising dye for biomolecule recognition was investigated in aprotic media and, for the first time, the direct radical anion-radical cation annihilation ECL was obtained.

[Ru(bpy)3]2+-doped silica nanoparticles within layer-by-layer biomolecular coatings and their application as a biocompatible electrochemiluminescent tag material

[Ru(bpy)3]2+-doped silica (RuSi) nanoparticles were synthesized by using a water/oil microemulsion method. Stable electrochemiluminescence (ECL) was obtained when the RuSi nanoparticles were immobilized on a glassy carbon electrode by using tripropylamine (TPA) as a coreactant. Furthermore, the ECL of the RuSi nanoparticles with layer-by-layer biomolecular coatings was investigated. Squential self-assembly of the polyelectrolytes and biomolecules on the RuSi nanoparticles gave nanocomposite suspensions, the ECL of which decreased on increasing the number of bilayers. Moreover, factors that affected the assembly and ECL signals were investigated. The decrease in ECL could be assigned to steric hindrance and limited diffusion of the coreactant molecules in the silica matrix after they were attached to the biomolecules. Since surface modification of the RuSi nanoparticles can improve their biocompatibility and prevent leaking of the [Ru(bpy)3]2+ ions, the RuSi nanoparticles can be readily used as efficient and stable ECL tag materials in immunoassay and DNA detection.

Bis(2,2'-bipyridine)(5,6-epoxy-5,6-dihydro-[1,10]phenanthroline)ruthenium: synthesis and electrochemical and electrochemiluminescence characterization

In this work, an electrochemiluminescence (ECL) reagent bis(2,2'-bipyridine)(5,6-epoxy-5,6-dihydro-[1,10]phenanthroline)ruthenium complex (Ru-1) was synthesized, and its electrochemical and ECL properties were characterized. The synthesis of Ru-1 was confirmed by IR spectra, element analysis, and (1)H NMR spectra. For further study, its UV-vis absorption and fluorescence emission spectra were investigated. Ru-1 also exhibited quasi-reversible Ru (II)/Ru (III) redox waves in acetonitrile solution. The aqueous ECL behaviors of Ru-1 were also studied in the absence and in the presence of tripropylamine. The complex was fabricated on a gamma-(aminopropyl) triethoxysilane (APTES) pretreated indium tin oxide (ITO) substrate via aminolysis reaction between the 5,6-epoxy-5,6-dihydro-[1,10]phenanthroline ligand and APTES. The resulting Ru-1 modified ITO substrate exhibited a broad absorption band in the visible region (350-600 nm) and its fluorescence emission spectrum was centered at 622 nm. The Ru-1 modified ITO electrode showed relative low ECL response. To improve the solid-state ECL response, a gold nanoparticles (GNP)/Ru-1 modified ITO electrode was constructed. The mixing of GNP and Ru-1 could produce the aggregates, which were further immobilized onto a 3-mercaptopropyltrimethoxy-silane (3-MPTMS) pretreated ITO substrate via Au-S interactions to construct the GNP/Ru-1 modified electrode.