Ru(bpy)3-doped silica nanoparticle DNA probe for the electrogenerated chemiluminescence detection of DNA hybridization

A sensitive electrogenerated chemiluminescence (ECL) detection of DNA hybridization, based on tris(2,2′-bipyridyl)ruthenium(II)-doped silica nanoparticles (Ru(bpy)₃²⁺-doped SNPs) as DNA tags, is described. In this protocol, Ru(bpy)₃²⁺-doped SNPs was used for DNA labeling with trimethoxysilylpropydiethylenetriamine(DETA) and glutaraldehyde as linking agents. The Ru(bpy)₃²⁺-doped SNPs labeled DNA probe was hybridized with target DNA immobilized on the surface of polypyrrole (PPy) modified Pt electrode. The hybridization events were evaluated by ECL measurements and only the complementary sequence could form a double-stranded DNA (dsDNA) with DNA probe and give strong ECL signals. A three-base mismatch sequence and a non-complementary sequence had almost negligible responses. Due to the large number of Ru(bpy)₃²⁺ molecules inside SNPs, the assay allows detection at levels as low as 1.0 × 10⁻¹³ mol l⁻¹ of the target DNA. The intensity of ECL was linearly related to the concentration of the complementary sequence in the range of 2.0 × 10⁻¹³ to 2.0 × 10⁻⁹ mol l⁻¹.     

EQCM study of the ECL quenching of the tris(2,2′-bipyridyl)ruthenium(II)/tris-n-propylamine system at a Au electrode in the presence of chloride ions

Significant effect of chloride ions on the electrogenerated chemiluminescence (ECL) behavior of the ruthenium(II)tris(2,2′-bipyridine) (Ru(bpy)₃²⁺)/tri-n-propylamine (TPrA) system at a Au electrode was reported. At low concentrations (e.g., [Cl⁻] < 5 mM), the ECL was enhanced; at relatively high concentrations, however, the ECL intensity decreased with the increase of the [Cl⁻]. At [Cl⁻] = 90 mM, ∼50% and 100% ECL inhibition was observed for the first and the second ECL wave, respectively. The electrogenerated gold-chloride complexes (AuCl₂⁻ and AuCl₄⁻) which were verified using an electrochemical quartz-crystal microbalance (EQCM) method were found to be responsible for the ECL inhibition. This study suggests that care must be taken when a Au working electrode is used for ECL studies in chloride-containing buffer solutions (widely used in DNA probes) and/or with the commonly used chloride-containing reference electrodes since in these cases the ECL behavior may significantly disagree with that obtained using other electrodes and reaction media.     

Characterization of electrochemiluminescence of tris(2,2′-bipyridine)ruthenium(II) with glyphosate as coreactant in aqueous solution

Glyphosate, a phosphorus-containing amino acid type herbicide was used as a coreactant for studying of electrochemiluminescence (ECL) reaction of tris(2,2′-bipyridyl)ruthenium(II) [Ru(bpy)₃²⁺] in an aqueous solution. In a phosphate buffer solution of pH 8, glyphosate itself was known to be electrochemically inactive at glassy carbon electrode, however, it participated in a homogeneous chemical reaction with the electrogenerated Ru(bpy)₃³⁺, and resulted in producing Ru(bpy)₃²⁺ species at the electrode surface. Kinetic and mechanistic information for the catalysis of glyphosate oxidation were evaluated by the steady-state voltammetric measurement with an ultramicroelectrode. The simulated cyclic voltammogram based on this mechanism was in good agreement with that obtained experimentally. ECL reaction of Ru(bpy)₃²⁺/glyphosate system was found to be strongly dependent on the media pH. In a pH region of 5-9, an ECL wave appeared at ca. +1.1 V vs. Ag/AgCl, which was caused by the generation of *Ru(bpy)₃²⁺ via a Ru(bpy)₃³⁺-mediated oxidation of glyphosate. When pH >10, a second ECL wave was observed at ca. +1.35 V vs. Ag/AgCl, which was believed to be associated with a reaction between Ru(bpy)₃³⁺ and the species from direct oxidation of GLYP at a GC electrode surface.     

Hydroxyl radical-related electrogenerated chemiluminescence reaction for a ruthenium tris(2,2′)bipyridyl/co-reactants system at boron-doped diamond electrodes

An electrogenerated chemiluminescence (ECL) reaction of the Ru(bpy)₃²⁺ (2,2′-bipyridyl, bpy)/co-reactant system in the extremely high-potential region (over 2.6 V versus Ag/AgCl) was probed using a boron-doped diamond (BDD) electrode. At the BDD electrode, three ECL waves (1.25, 2.30 and 3.72 V) were observed in cyclic voltammograms for 20 mM ascorbic acid (AA). For the ECL peaks observed at 1.25 V corresponding to the oxidation potential for Ru(bpy)₃²⁺ (1.15 V), the light intensities and current densities were found to depend on the square root of the AA concentration. This suggests that AA oxidation, followed by the formation of the reducing radical that is necessary for generating the excited state of Ru(bpy)₃^2+* occurred through homogeneous electron-transfer between Ru(bpy)₃³⁺ and the AA species. However, for the ECL peaks at 2.30 V, the current densities and light intensities linearly increased with increasing AA concentration, suggesting that the reducing radical was formed through the direct oxidation at the electrode surface. The ECL reaction at 3.72 V was observed only at the BDD electrode and not at other electrodes. The onset potentials for the light intensity were approximately 2.6 V, independently of the type of the co-reactants (e.g. 2-propanol and AA). The peak potentials exhibited linear relation with the co-reactant concentration. In the analysis of the ECL intensity for various co-reactants (alcohols) that show different reactivity for the hydrogen abstraction reaction, the order of the light intensities at the peaks for alcohols was found to be consistent with that for the rate constants of the hydrogen abstraction reaction. These results indicate that the co-reactant radical was formed through the hydrogen abstraction reaction with the hydroxyl radical (HO) generated during the oxygen evolution reaction.     

Mediated oxidation of guanine by [Ru(bpy)2dpp] and their electrochemical assembly on the ITO electrode

Electrochemical oxidation of guanine mediated by [Ru(bpy)₂dpp]²⁺ (where bpy = 2,2′-bipyridine, dpp = 2,3-bis (2-pyridyl) pyrazine) and their electrochemical assembly at an ITO electrode prompted by guanine have been investigated with cyclic voltammetry and differential pulse voltammetry. It is found that [Ru(bpy)₂dpp]²⁺ can serve as an excellent mediator to induce the oxidation of guanine, and the mediated peak currents increase linearly with the rise of guanine concentration in the range from 0.01 to 0.20 mmol L⁻¹. Interestingly, with the increase of repetitive voltammetric sweeping numbers, [Ru(bpy)₂dpp]^3+/2+ can be assembled onto the ITO electrode and guanine has the ability to enhance the peak currents of prewaves. Also, with the rise of guanine concentration from 0.01 to 0.15 mmol L⁻¹, the peak currents of prewaves increase gradually. Meanwhile, the mediated mechanism of guanine oxidation by [Ru(bpy)₂dpp]²⁺ and the assembled process of [Ru(bpy)₂dpp]^3+/2+ on the ITO surface in the presence of guanine are discussed in detail.     

Detection of N-methyladenosine in urine samples by electrochemiluminescence using a heated ITO electrode

A sensitive and rapid electrochemiluminescence (ECL) method for the detection of N⁶-Methyladenosine (m6A) in urine samples on a heated indium-tin-oxide (ITO) electrode is presented. The ECL intensity of Tris(2,2′-bipyridyl) dichlororuthenium(II)hexahydrate (Ru(bpy)₃²⁺) can be enhanced by the presence of m6A. Experimental results showed that the change of ECL intensities (ΔI) of the Ru(bpy)₃²⁺ between before and after addition of m6A was affected by the working electrode surface temperature (T_e); the highest ΔI occurred at 31 °C. Under optimum conditions, the ΔI had a linear relationship with the m6A concentration in the range of 1.9 × 10⁻⁹-3.9 × 10⁻⁶ mol/L and a detection limit of 7.7 × 10⁻¹⁰ mol/L (S/N = 3) at T_e = 31 °C. The recovery of m6A standards added to urine samples verified the accuracy of the proposed method.     

An electrochemiluminescent biosensor for vitamin C based on inhibition of luminol electrochemiluminescence on graphite/poly(methylmethacrylate) composite electrode

A novel graphite/poly(methyl methacrylate) (graphite/PMMA) electrode was prepared in this paper. It was found that the developed polymer graphite paste electrode has some advantages in electrochemistry and electrochemiluminescence (ECL), such as high sensitivity, good reproducibility, quick and wide linear range of response to some biomolecules. The ECL behavior of luminol has been investigated in detail at the graphite/PMMA electrode, and vitamin C was found to be able to inhibit this ECL system. Based on which an inhibited ECL detection method has been developed for determination of vitamin C in this paper. The proposed method exhibited good reproducibility, wide-range linearity, high sensitivity and stability with a detection limit of 8.3 × 10⁻⁹ mol L⁻¹ (signal-to-noise ratio = 3) and linear response range of 2.5 × 10⁻⁸-1.0 × 10⁻⁴ mol L⁻¹. The relative standard deviation was 2.3% for 5 × 10⁻⁶ mol L⁻¹ vitamin C (n = 9). The possible mechanism for inhibition of luminol on graphite/PMMA electrode has also been proposed.     

Enhanced solid-state electrogenerated chemiluminescence of Au/CdS nanocomposite and its sensing to H2O2

Au nanoparticles (AuNPs) are good quenchers once they closely contact with luminophore. Here we reported a simple approach to obtain enhanced electrogenerated chemiluminescence (ECL) behavior based on Au/CdS nanocomposite films by adjusting the amount of AuNPs in the nanocomposite. The maximum enhancement factor of about 4 was obtained at an indium tin oxide (ITO) electrode in the presence of co-reactant H₂O₂. The mechanism of this enhancement was discussed in detail. The strong ECL emission from Au/CdS nanocomposites film was exploited to determine H₂O₂. The resulting ECL biosensors showed a linear response to the concentration of H₂O₂ ranging from 1.0 × 10⁻⁸ to 6.6 × 10⁻⁴ mol L⁻¹ with a detection limit of 5 nmol L⁻¹ (S/N = 3) and good stability and reproducibility.     

Efficient green-colored electrochemiluminescence from cyclometalated iridium(III) complex

The spectroscopy, electrochemistry, and electrochemiluminescence (ECL) of cyclometalated iridium(III) bis(2-(p-tolyl)pyridinato-N, C^2′) (picolinate) [(tpy)₂Ir(pico)] was investigated. (tpy)₂Ir(pico) shows high photoluminescence efficiency (Φ_PL = ∼0.31) and quasi-reversible redox behaviors in acetonitrile solution. Intense green ECL was observed from all three modes of ECL generation (annihilation, oxidative-reduction, and reductive-oxidation). Relative ECL efficiencies with or without coreactants from (tpy)₂Ir(pico) were estimated using Ru(bpy)₃²⁺ (bpy, 2,2′-bipyridine) as a relative standard. Typically, in the reductive-oxidation process with peroxodisulfate (S₂O₈²⁻), (tpy)₂Ir(pico) produces 8-fold more efficient ECL at approximately 531 nm than Ru(bpy)₃². This efficient green ECL indicates potential for the development of multicolored ECL analysis in addition to standard Ru(bpy)₃²⁺ systems.     

The ultrasonic electropolymerization of an 5-[o-(4-bromine amyloxy)phenyl]-10,15,20-triphenylporphrin (o-BrPETPP) film electrode and its electrocatalytic properties to dopamine oxidation in aqueous solution

5-[o-(4-Bromine amyloxy)phenyl]-10,15,20-triphenylporphrin (o-BrPETPP) was electropolymerized on a glassy carbon electrode (GCE), and the electrocatalytic properties of the prepared film electrode response to dopamine (DA) oxidation were investigated. A stable o-BrPETPP film was formed on the GCE under ultrasonic irradiation through a potentiodynamic process in 0.1 M H₂SO₄ between −1.1 V and 2.2 V versus a saturated calomel electrode (SCE) at a scan rate of 0.1 V s⁻¹. The film electrode showed high selectivity for DA in the presence of ascorbic acid (AA) and uric acid (UA), and a 6-fold greater sensitivity to DA than that of the bare GCE. In the 0.05 mol L⁻¹ phosphate buffer (pH 6.0), there was a linear relationship between the oxidation current and the concentration of DA solution in the range of 5 × 10⁻⁷ mol L⁻¹ to 3 × 10⁻⁵ mol L⁻¹. The electrode had a detection limit of 6.0 × 10⁻⁸ mol L⁻¹(S/N = 3) when the differential pulse voltammetric (DPV) method was used. In addition, the charge transfer rate constant k = 0.0703 cm s⁻¹, the transfer coefficient α = 0.709, the electron number involved in the rate determining step n_α = 0.952, and the diffusion coefficient D_o = 3.54  10⁻⁵ cm² s⁻¹ were determined. The o-BrPETPP film electrode provides high stability, sensitivity, and selectivity for DA oxidation.     

Amperometric flow injection analysis as a new approach for studying disperse systems

Fast and simple quantitative determination in dispersed systems (layered double hydroxides - LDHs - suspensions in aqueous solutions) was performed by a procedure that couples flow injection and amperometric detection (FI-AM). LDH dispersions are injected in a continuous flow (1 mL min⁻¹) of 0.05 mol L⁻¹ KNO₃ solution and [Cu(H₂O)₆]²⁺, used as a probe, is detected at a glassy carbon electrode housed in a flat electrochemical cell. The current intensity, recorded at the selected working potential (−0.25 V vs Ag/AgCl/NaCl (3 mol L⁻¹)), presents a linear relationship with [Cu(H₂O)₆]²⁺ concentration and the procedure offers high sensitivity (slope = 0.036 μA/(μmol L⁻¹)), a low detection limit (=0.7 μmol L⁻¹) and a wide quantification range (4-200 μmol L⁻¹).The method was applied to [Cu(H₂O)₆]²⁺ determination in two particular LDH-aqueous solution dispersed systems: (1) [Cu(H₂O)₆]²⁺ scavenging by etilendiammintetraacetic acid (EDTA) modified Zn-Al-LDHs, and (2) [Cu(H₂O)₆]²⁺ release from a copper doped Mg-Al-LDHs. The results obtained are comparable to those reported in previous works using different quantification techniques. FI-AM determination is applied without sample pretreatment (solid-supernatant separation) providing a high sampling rate (above 120 samples h⁻¹) that allows a better comprehension of the processes, particularly at the initial stages.     

A highly sensitive method for detection of protein based on inhibition of Ru(bpy)32+/TPrA electrochemiluminescent system

The detection of proteins is very important in the study of biochemistry procedure, and electrochemiluminescence method is a very practical tool for the study of protein folding, structure and quantification. In this work, bovine serum albumin (BSA) and casein were found to be able to significantly quench the electrochemiluminescence (ECL) of Ru(bpy)₃²⁺/TPrA system, based on which a highly sensitive approach for the detection of protein was proposed. Under the optimized conditions, the logarithmic plot of the inhibited ECL versus the concentration of BSA and casein were linear over the ranges of 1–30 μg/L and 0.1–1.6 μg/L, respectively. The corresponding limit of detection (LOD) was 0.45 μg/L for BSA and 0.026 μg/L for casein (S/N = 3). UV, ECL and fluorescence methods were used to investigate the mechanism of the inhibited ECL of Ru(bpy)₃²⁺/TPrA/BSA system. A mechanism based on the formation of protein-Ru(bpy)₃²⁺ super molecule was proposed, which would prevent Ru(bpy)₃²⁺ from reaching the working electrode surface so that induced ECL quenching.     

Electrochemical fabrication and potential-enhanced luminescence of [Ru(bpy)2tatp] incorporating DNA-stabilized single-wall carbon nanotubes on an indium tin oxide electrode

A simple method was developed for the preparation of [Ru(bpy)₂tatp]²⁺-based aggregates (where bpy = 2,2′-bipyridine, tatp = 1,4,8,9-tetra-aza-triphenylene) on an indium tin oxide (ITO) electrode in the presence of DNA-stabilized single-walled carbon nanotubes (DNA–SWCNTs). The presence of SWCNTs in the concentration range from 0.02 to 0.125 g L⁻¹ dispersed with 0.25 mmol L⁻¹ DNA was found to promote the immobilization of [Ru(bpy)₂tatp]²⁺ on the ITO electrode by the method of repetitive voltammetric sweeping. The photoluminescence of [Ru(bpy)₂tatp]²⁺ incorporating DNA–SWCNTs both in solution and on the ITO electrode was systematically investigated by emission spectra and fluorescence microscopic imaging. An excess amount of SWCNTs can quench the photoluminescence of [Ru(bpy)₂tatp]²⁺ enhanced by DNA. The anodic potentials combined with CW green laser via an optical microscope was found to significantly increase the emission intensity of [Ru(bpy)₂tatp]²⁺–DNA–SWCNTs aggregates on the ITO electrode. In addition, the electrochemical fabrication and photoluminescence principles of [Ru(bpy)₂tatp]²⁺–DNA–SWCNTs aggregates on the ITO electrode tuned by the external electric fields were discussed in detail.     

Study of the potentiometric response of the doped spinel Li1.05Al0.02Mn1.98O4 for the optimization of a selective lithium ion sensor

In this paper, we studied the development of a selective lithium ion sensor constituted of a carbon paste electrode modified (CPEM) with an aluminum-doped spinel-type manganese oxide (Li_1.05Al_0.02Mn_1.98O₄) for investigating the influence of a doping ion in the sensor response. Experimental parameters, such as influence of the lithium concentration in the activation of the sensor by cyclic voltammetry, pH of the carrier solution and selectivity for Li⁺ against other alkali and alkaline-earth ions were investigated. The sensor response to lithium ions was linear in the concentration range 5.62 × 10⁻⁵ to 1.62 × 10⁻³ mol L⁻¹ with a slope 100.1 mV/decade over a wide pH 10 (Tris buffer) and detection limit of 2.75 × 10⁻⁵ mol L⁻¹, without interference of other alkali and alkaline-earth metals, demonstrating that the Al³⁺ doping increases the structure stability and improves the potentiometric response and sensitivity of the sensor. The super-Nernstian response of the sensor in pH 10 can be explained by mixed potential arising from two equilibria (redox and ion-exchange) in the spinel-type manganese oxide.     

Influence of nature, concentration and pH of buffer acid-base system on rate determining step of the electrochemiluminescence of Ru(bpy)3 with tertiary aliphatic amines

The electrogenerated chemiluminescence (ECL) of Ru(bpy)₃²⁺ (bpy = 2,2′-bipyridyl) with tertiary aliphatic amines as co-reactants, was theoretically and experimentally studied as a function of the pre-equilibria involved in the ammonium proton lost and in relation to the nature of the rate determining step. Transient potential steps were used with a 3-mm glassy carbon disk electrode or carbon fiber ultramicroelectrodes array to investigate emission behavior in a variety of aqueous solution types, containing phosphate, tartrate and phthalate acid-base systems at differing pH values. The emission of Ru(bpy)₃²⁺ resulting from the reaction with n-tripropylamine (TPrA), tri-isobutylamine (TisoBuA), n-tributylamine (TBuA), methyl-di-n-propylamine (MeDPrA) and triethylamine (TEtA) in varying acid-base media was interpreted on the basis of the quoted pre-equilibria, ammonium pK_a being known. The nature of the rate determining steps changes depending on pH. Above pH ≈ 5 the amine neutral radical formation is the rate determining step and, is independent of pH with rate constant close to 10³ s⁻¹; below pH ≈ 5 the rate determining step becomes the deprotonation of the ammonium ion, operated by different bases present in solution. Different amines in the same acid-base system showed analogous ECL behavior, conditioned by the chosen acid base system. A single amine in different acid-base systems showed different kinetic behaviors, due to the dissociation constants of the chosen buffers. The concentration of the acid-base system also played an important role and influenced emission intensity and shape. ECL emission were simulated by finite difference methods, implementing a previously proposed mechanism by including the relevant pre-equilibria. Simulation may also give estimates of the pK_a values of the ammonium ions. An ion pair formation between R₃N⁺ and the mostly charged species present in solution is hypothesized to explain the contradictory experimental results concerning the reaction mechanism of the proton lost of the radical cation.     

DNA-promoted electrochemical assembly of [Ru(bpy)2dpp] on the ITO electrode by introducing copper(II) ion

The electrochemical assembly of [Ru(bpy)₂dpp]^3+/2+ (where bpy = 2,2′-bipyridine, dpp = 2,3-bis (2-pyridyl) pyrazine) promoted by calf thymus DNA on an ITO electrode based on the introduction of copper(II) ion has been investigated. There exists a diffusion-controlled wave and two prewaves for the complex in the differential pulse voltammetric sweeping process. The formal potential of the high prewave shift ca. 0.530 V negatively compared with that of the diffusion-controlled wave. Dpp ligand with two vacant chelating N sites in the complex can bite Cu²⁺ and the resultant heterometallic complex shows a weakened assembly in contrast to that of [Ru(bpy)₂dpp]^3+/2+ alone. Furthermore, double stranded DNA is able to accelerate the assembly of the ruthenium complex and heterometallic complex generated by chelating with Cu²⁺ by using the ITO surface, the prompted strength of the latter is far stronger than the former. Their assembled mechanism enhanced by DNA is proposed.     

DNA-enhanced assembly of [Ru(bpy)2ITATP] on an ITO electrode

A novel technique for controllable assembly of [Ru(bpy)₂ITATP]^3+/2+ (where bpy = 2,2′-bipyridine, ITATP = isatino[1,2-b]-1,4,8,9-tetraazatriphenylene) on an ITO electrode in the absence and presence of calf thymus DNA is proposed. The [Ru(bpy)₂ITATP]^3+/2+ and double stranded DNA is assembled onto the ITO electrode using repetitive voltammetric sweeping. The assembly is confirmed by ex situ cyclic voltammetry and the fluorescence microscopy. A pair of diffusion-controlled waves and prewaves for [Ru(bpy)₂ITATP]^3+/2+ is observed in the voltammetric sweeping process. The formal potential of the prewaves is found to be much negative than that of the diffusion-controlled waves. The controllable assembly of [Ru(bpy)₂ITATP]^3+/2+ on the ITO surface is accelerated by DNA and affected by ionic strength. With this DNA-prompted electrochemical technique, a multifunctional biomolecular film containing surface-confined redox center of controllable thickness is fabricated.     

Influence of metal coordination on conductivity behavior in poly(butadiene-acrylonitrile)-CoCl2 system

The metal complex formation and the electrical properties of amorphous solid polymer electrolytes, based on poly(butadiene-acrylonitrile) copolymer (PBAN) and CoCl₂, have been studied over the homogeneity region of the system limited by the CoCl₂ concentration of 1.89 mol kg⁻¹. It has been found that ionic conductivity is carried out by the unipolar anion transfer at lower CoCl₂ concentrations (up to 0.10 mol kg⁻¹). As the CoCl₂ concentration increases, electronic conductivity appears in addition to ionic conductivity, and the former becomes dominant, starting from 0.38 mol kg⁻¹. It has been shown that the nature of charge carriers is determined by the composition of metal complexes formed by CoCl₂ and the macromolecular solvent PBAN. At lower concentrations, the [Co₂L₂Cl₄]⁰ dimers are the predominant species (L being macromolecule side groups CN), and their dissociation is followed by the formation of mobile Cl⁻ anions and immobile binuclear [Co₂Cl₃]⁺ complexes. As CoCl₂ concentration increases, polynuclear [Co_nL₂Cl_2n]⁰ (n > 2) complexes appear (L being CN and CC groups of PBAN). Specific features of chemical bonds in π-complexes of transition metals result in the appearance of electronic charge carriers. The abrupt increase in conductivity observed at the highest CoCl₂ concentration is connected with the formation of a percolation network of polynuclear [Co_nL₂Cl_2n]⁰ complexes.     

Direct electrochemistry and electrocatalysis of cytochrome c based on chitosan-room temperature ionic liquid-carbon nanotubes composite

A robust and effective composite film combined the benefits of room temperature ionic liquid (RTIL), chitosan (Chi) and multi-wall carbon nanotubes (MWNTs) was prepared. Cytochrome c (Cyt c) was successfully immobilized on glassy carbon electrode (GCE) surface by entrapping in the composite film. Direct electrochemistry and electrocatalysis of immobilized Cyt c were investigated in detail. A pair of well-defined and quasi-reversible redox peaks of Cyt c was obtained in 0.1 mol L⁻¹ pH 7.0 phosphate buffer solution (PBS), indicating the Chi-RTIL-MWNTs film showed an obvious promotion for the direct electron transfer between Cyt c and the underlying electrode. The immobilized Cyt c exhibited an excellent electrocatalytic activity towards the reduction of H₂O₂. The catalysis current was linear to H₂O₂ concentration in the range of 2.0 × 10⁻⁶ to 2.6 × 10⁻⁴ mol L⁻¹, with a detection limit of 8.0 × 10⁻⁷ mol L⁻¹ (S/N = 3). The apparent Michaelis-Menten constant (K_m) was calculated to be 0.45 ± 0.02 mmol L⁻¹. Moreover, the modified electrode displayed a rapid response (5 s) to H₂O₂, and possessed good stability and reproducibility. Based on the composite film, a third-generation reagentless biosensor could be constructed for the determination of H₂O₂.     

DNA-promoted electrochemical assembly of [Ru(bpy)2IP] at an ITO electrode

A controllable assembly technique of [Ru(bpy)₂IP]^3+/2+ (where bpy = 2,2′-bipyridine and IP = imidazo[4,5,f][1,10]phenanthroline) promoted by calf thymus DNA at an ITO electrode is proposed. The stable assembled layer containing [Ru(bpy)₂IP]^3+/2+ and double stranded DNA is obtained on the ITO electrode using repetitive voltammetric sweeping, confirmed by ex situ voltammetry, X-ray photoelectron spectroscopy (XPS) and the inverted fluorescence microscopy. There exist two pairs of diffusion-controlled waves and two pairs of prewaves for [Ru(bpy)₂IP]²⁺ in the voltammetric sweeping process. The half-wave potentials of the prewaves are far more negative than those of the diffusion-controlled waves. These experimental results suggest that double stranded DNA is enable to accelerate and increase the controllable assembly of Ru(bpy)₂IP]^3+/2+ by using the ITO surface. The fluorescence microscopy imaging reveals that [Ru(bpy)₂IP]^3+/2+ has the ability to bind with double strand DNA. The fluorescence intensity of [Ru(bpy)₂IP]^3+/2+ with DNA is stronger than that without DNA.