Annihilation Electrochemiluminescence Research Articles

Enhancing aqueous stability and radiative-charge-transfer efficiency of CsPbBr3 perovskite nanocrystals via conductive silica gel coating

The poor aqueous stability of perovskite nanocrystals (NCs) limits their electrochemical applications. Herein, we reported a waterproof and conductive silica gel shell encapsulating CsPbBr3 NCs, enhancing its aqueous stability and radiative-charge-transfer efficiency. Upon introducing small volume of CsBr aqueous solution in hexane containing tetramethoxysilane (TMOS) and Cs4PbBr6 NCs, the conversion reaction of Cs4PbBr6 → CsPbBr3+3CsBr was triggered to form Cs4PbBr6@CsPbBr3@silica gel (CsBr) hybrid. The silica gel shell can block the contact between CsPbBr3 NCs and bulk aqueous phase. The CsBr enclosed in the silica gel can reduce the conversion rate and increase dramatically the electrical conductivity of the silica gel. The electrochemiluminescence (ECL) of CsPbBr3 NCs in aqueous phase was enhanced greatly. The strong ECL of CsPbBr3 NCs in the hybrid was still observed after stored in CsBr solution for 30 day. The as-obtained perovskite hybrid displays improved electrochemical charge-injecting performance and radiative-charge-transfer in ECL. Annihilation ECL demonstrates that all the electrons injected onto the perovskite hybrid can recombine with the holes injected onto it for light-emitting. Both annihilation and co-reactant ECL, as well as photoluminescence reveal that encapsulating CsPbBr3 NCs into a conductive and waterproof silica gel shell is favorable to enhance aqueous performance of perovskite NCs with negligible effects on their excited states. The ECL of the core-shell perovskite hybrid was applied to detect dopamine in the concentration range of 0.01–10 μM, with the limit of detection of 3 nM.

Towards Determining Kinetics of Annihilation Electrogenerated Chemiluminescence by Concentration-Dependent Luminescent Intensity

In ion-annihilation electrochemiluminescence (ECL), luminophore ions are generated by oxidation as well as reduction at electrodes surfaces, and subsequently recombine into an electronically excited state, which emits light. The intensity of the emitted light is often limited by the kinetic rate of recombination of the luminophore ion species. Recombination or annihilation rates are high ranging up to approximately 1010 M−1 s−1 and can be difficult to determine using scanning electrochemical microscopy or high-frequency oscillations of an electrode potential. Here, we propose determining annihilation kinetics by measuring the relative change of the emitted light intensity as a function of luminophore concentration. Using finite element simulations of annihilation ECL in a geometry of two closely spaced electrodes biased at constant potentials, we show that, with increasing concentrations, luminescence intensity crosses over from a quadratic dependence on concentration to a linear regime—depending on the rate of annihilation. Our numerical results are applicable to scanning electrochemical microscopy as well as nanofluidic electrochemical devices to determine fast ion-annihilation kinetics.

Promising Anodic Electrochemiluminescence of Nontoxic Core/Shell CuInS2/ZnS Nanocrystals in Aqueous Medium and Its Biosensing Potential.

Copper indium sulfide (CuInS2, CIS) nanocrystals (NCs) are a promising solution to the toxic issue of Cd- and Pb-based NCs. Herein, electrochemiluminescence (ECL) of CIS NCs in aqueous medium is investigated for the first time with l-glutathione and sodium citrate-stabilized water-soluble CIS/ZnS NCs as model. The CIS/ZnS NCs can be oxidized to hole-injected states via electrochemically injecting holes into valence band at 0.55 and 0.94 V (vs Ag/AgCl), respectively. The hole-injected state around 0.94 V can bring out efficient oxidative-reduction ECL with a similar color to Ru(bpy)32+ in the presence of tri- n-propylamine (TPrA) and enable CIS/ZnS NCs promising ECL tags with l-glutathione as linker for labeling. The ECL of CIS/ZnS NCs/TPrA can be utilized to determine vascular endothelial growth factor (VEGF) from 0.10 to 1000 pM with the limit of detection at 0.050 pM (S/N = 3). Although the hole-injected state around 0.55 V is generated ahead of oxidation of TPrA and fails to bring out coreactant ECL, annihilation ECL proves that both hole-injected states generated, at 0.55 and 0.94 V, can be involved in electrochemical redox-induced radiative charge transfer by directly stepping CIS/ZnS NCs from electron-injecting potential to hole-injecting potential. CIS/ZnS NCs are promising nontoxic electrochemiluminophores with lowered ECL triggering potential around 0.55 V for less electrochemical interference upon the development of coreactant.

Oxygen Containing Functional Groups Dominate the Electrochemiluminescence of Pristine Carbon Dots

In this study, electrochemiluminescence (ECL) properties of carbon dots (CDs, less than 10 nm) have been investigated. Such CDs were fabricated via electrochemical etching strategy from graphite rods. Subsequently, a series of CDs were prepared through controlled surface engineering technique by a wet chemical method, including the oxidized-CDs (oCDs), partially reduced-CDs (rCDs), and fully reduced-CDs (F-rCDs). In-depth characterizations including UV–vis, FT-IR, Raman, XPS, etc. revealed significant differences in features of these CDs, especially the condition of surface grafted oxygen containing functional groups. ECL results suggested that all of the annihilation ECL of CDs, oCDs, and rCDs demonstrated a stable positively charged luminophore (R+•) and an unstable negatively charged luminophore (R–•) at the surface of GCE and possessed a 365 nm emission peak and consistent emission range from 550 to 850 nm. During further structural mode investigation and ECL properties simulation, the surface constru...

Efficient Annihilation Electrochemiluminescence of Cationic Helicene Luminophores

AbstractThe electrochemistry and annihilation electrochemiluminescence (ECL) of a series of chiral cationic helicene luminophores containing various substituents were investigated in acetonitrile solvent. The electrochemical characterization evidenced a systematic reversible reduction of cationic derivatives, whereas the oxidation could be reversible or not, depending on the nature of the core heteroatoms within the structure as well as the functional‐group appendages. One of the key parameters governing the ECL intensity is, indeed, the formal redox potentials for the electrogeneration of the neutral radical and dication radical species, which will undergo the annihilation reaction. On that basis, a thermodynamic wall of efficiency was proposed in the case of ECL annihilation pathway to predict the formation efficiency of the emitting excited state and, eventually, the light emission‘s strength. This very simple wall is constructed by plotting the difference of formal potentials in function of the fluorescence wavelength, thus delimiting two domains where ECL is thermodynamically possible or unfavorable.

Yellow electrochemiluminescence emission from hydrophilic poly[(9,9-di-(2-ethylhexyl)-9H-fluorene-2,7-vinylene)-co-(1-methoxy-4-(2-ethylhe-xyloxy)-2,5-phenylenevinylene)] (PFV) conjugated polymer dots capped with Triton X-100 in aqueous solution

We synthesized new, yellow-light emitting, and hydrophilic poly[(9,9-di-(2-ethylhexyl)-9H-fluorene-2,7-vinylene)-co-(1-methoxy-4-(2-ethylhe-xyloxy)-2,5-phenylenevinylene)] conjugated polymer dots capped with nonionic surfactant Triton X-100 (PFV CP-dots@TX), immobilized them on glassy carbon electrodes and studied their electrochemiluminescence (ECL) behaviors and mechanisms in aqueous solutions. The ECL activities of the hydrophilic CP-dots were investigated by applying the glassy carbon working electrode with pulse potential between anodic and cathodic potentials in the absence of coreactant, with sweeping anodic potential in the presence of Tri-n-propylamine (TPrA) as the coreactant, and with sweeping cathodic potential in the presence of peroxydisulfate (S2O82−) as the coreactant. Experimental results shows that PFV CP-dots@TX have good annihilation ECL activity, anodic ECL activity and cathodic ECL activity. All of the three types of ECL reactions emit yellow light with the maximum wavelength of 573nm, which is the same as the fluorescence emission spectrum of PFV CP-dots@TX in water. The energies involved in the ECL reactions were analyzed and non-surface state ECL mechanisms were discussed and proposed. The yellow light-emitting, hydrophilic CP-dots are envisioned to be a new type of ECL luminophores that may have promising applications in chemical sensing, biosensing and new optoelectronic devices.

Anodic, Cathodic, and Annihilation Electrochemiluminescence Emissions from Hydrophilic Conjugated Polymer Dots in Aqueous Medium

Hydrophilic poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) conjugated polymer dots (CP-dots) capped by Triton X-100 were synthesized. For the first time, the electrochemiluminescence (ECL) emission of CP-dots was investigated in aqueous solution. At the glassy carbon/water interface, the CP-dots have excellent and multichannel ECL properties, such as having annihilation ECL activity in the absence of coreactants, and give bright anodic and cathodic ECL emission (590 nm) in the presence of tri-n-propylamine (TPrA) and peroxydisulfate (S2O8(2-)), respectively. The versatile ECL properties of the hydrophilic CP-dots combined with their low cytotoxicity, good biocompatibility, and easy bioconjugation may suggest promising applications of this new type of ECL nanomaterial in novel biosensing and bioimaging, and new types of light-emitting devices.

Simultaneous control of spectroscopic and electrochemical properties in functionalised electrochemiluminescent tris(2,2′-bipyridine)ruthenium(ii) complexes

Using a combination of electrochemical, spectroscopic and computational techniques, we have explored the fundamental properties of a series of ruthenium diimine complexes designed for coupling with other molecules or surfaces for electrochemiluminescence (ECL) sensing applications. With appropriate choice of ligand functionality, it is possible to manipulate emission wavelengths while keeping the redox ability of the complex relatively constant. DFT calculations show that in the case of electron withdrawing substituents such as ester or amide, the excited state is located on the substituted bipyridine ligand whereas in the case of alkyl functionality it is localised on a bipyridine. The factors that dictate annihilation ECL efficiency are interrelated. For example, the same factors that determine ΔG for the annihilation reaction (i.e. the relative energies of the HOMO and LUMO) have a corresponding effect on the energy of the excited state product. As a result, most of the complexes populate the excited state with an efficiency (Φ(ex)) of close to 80% despite the relatively wide range of emission maxima. The quantum yield of emission (Φ(p)) and the possibility of competing side reactions are found to be the main determinants of ECL intensity.

Electrochemiluminescence from direct electro-oxidations of organic analyte rutin and its analytical application

This paper reported an electrochemiluminescence (ECL) from direct electrochemical oxidation of organic analyte rutin itself that was different from both annihilation and coreactant ECL in mechanism. The ECL production mechanism could be described as follows: rutin was electrochemically oxidized via one-electron transfer to o-semiquinone radical. Then the radical was further electrochemically oxidized via one-electron transfer to the excited state rutin o-quinone that subsequently emitted light. Based on the ECL of rutin, a flow injection ECL method for the determination of rutin was proposed. In the proposed flow injection system, an ECL signal was generated in rutin–NaOH–cetyl trimethyl ammonium chloride solution by applying direct current of 12 mA to the platinum anode in an ECL flow-through cell with two-electrode system. The ECL intensity of rutin was proportional to its concentration over the range of 6.0 × 10 −7–1.0 × 10 −5 mol l −1, and the limit of detection ( s/ n = 3) is 2 × 10 −7 mol l −1. The proposed method had been evaluated by the analysis of rutin in pharmaceutical preparations.

Electrochemiluminescence from successive electro- and chemo-oxidation of rifampicin and its application to the determination of rifampicin in pharmaceutical preparations and human urine

A novel electrochemiluminescence (ECL) type was proposed based on successive electro- and chemo-oxidation of oxidable analyte, which was different from both annihilation and coreactant ECL types in mechanism. Rifampicin was used as a model compound. No any chemiluminescence (CL) was produced by either electrochemical oxidation or chemical oxidation of rifampicin in KH 2PO 4–Na 2B 4O 7 (pH 6.6) buffer–dodecyl trimethyl ammonium chloride (DTAC) solution. However, an ECL was observed by electrochemical oxidization of rifampicin in the same solution in the presence of oxidant such as dissolved oxygen, activated oxygen and potassium peroxydisulfate (K 2S 2O 8). The ECL was attributed to electrochemical oxidation of rifampicin to form semiquinone free radical, and then subsequently chemical oxidation of the formed radical by oxidant to form excited state rifampicin quinone. The proposed ECL type introduced additional advantages such as high selectivity, simple and convenient operation, and effective avoidance of side reaction that often took place in homogenous CL reaction, and will open a novel application field. In addition, with the ECL in the presence of K 2S 2O 8 as oxidant, a flow injection ECL method for the determination of rifampicin was proposed. The ECL intensity was linear with rifampicin concentration in the range of 1.0 × 10 −7 to 4.0 × 10 −5 mol l −1 and the limit of detection (s/n = 3) was 3.9 × 10 −8 mol l −1. The proposed method was applied to the determination of rifampicin in pharmaceutical preparations and human urine.