The redox nature and electrochemiluminescence (ECL) of highly crystallized organometal halide perovskite CH3NH3PbBr3 nanocrystals (NCs) in aqueous medium were investigated for the first time. CH3NH3PbBr3 NCs could be electrochemically reduced to negative charge states by injecting electrons into the lowest unoccupied molecular orbitals and oxidized to positive charge states by removing electrons from the highest occupied molecular orbitals; charge transfer between NCs with positive and negative charge states could produce ECL. The redox sequence of CH3NH3PbBr3 NCs played an important role in the generation of charge-transfer-mediated ECL; transient ECL could be achieved only by electrochemically reducing positive-charged NCs in an annihilation route. A large redox current was unfavorable for ECL. Charge mobility within CH3NH3PbBr3 NCs had an important effect on ECL intensity in a co-reactant route, which is promising for photovoltaic and optoelectronic device applications. Importantly, the ECL spectra of CH3NH3PbBr3 NCs were almost identical to their photoluminescence spectra, with a maximum emission around 535 nm and full width at half-maximum around 25 nm; this might open a way to obtaining monochromatic ECL using highly crystallized NCs as emitters, which makes them promising for use in color-selective ECL analysis.

A spectrum-resolved dual-color electrochemiluminescence (ECL) immunoassay was designed and implemented to simultaneously detect carcinoembryonic antigen (CEA) and alpha fetoprotein (AFP) with CdTe (λmax = 776 nm) and CdSe (λmax = 550 nm) nanocrystals (NCs) as ECL tags. The CdTe and CdSe NCs were labeled with respective probe antibodies (Ab2) of CEA and AFP, respectively, and then immobilized onto the working electrode surface via sandwich-type immunoreactions. Both CdTe and CdSe NCs within the NCs immunocomplexes can be electrochemically reduced and simultaneously give off monochromatic ECL emissions in the near-infrared and greenish regions, respectively, when (NH4)2S2O8 was used as a cathodic ECL coreactant. The ECL spectra of the two surface-confined NCs were well separated and had no cross energy-transfer interactions, which made the dual-color immunoassay highly selective and sensitive toward respective target analytes. With the proposed ECL biosensor, CEA and AFP were simultaneously detected and quantified with an extremely low detection limit of 1 pg/mL for CEA and 10 fg/mL for AFP, respectively. This work demonstrated the probability of performing multianalyte assays via a spectrum-resolved ECL strategy with improved sensitivity and signal-to-noise ratio as compared to NCs-based fluorescent multianalyte assays.

Copper indium sulfide (CIS) nanocrystals (NCs) are a promising solution to the toxicity issue of Cd- and Pb-based NCs. Herein, electrochemical redox-induced radiative charge transfer in p-type CIS NCs was explored for the first time by electrochemiluminescence (ECL). The CIS NCs displayed a weak reductive process for injecting electrons into the conduction band (CB) and four strong oxidative processes for injecting holes into the valence band (VB). Potential-resolved ECL demonstrated that the electrochemically injected CB electrons were stable in the CIS NCs and could recombine with Cu2+ defects (preexisting in the CIS NCs and/or generated via electrochemically oxidizing the CIS NCs) for radiative charge transfer in the CIS NCs. Annihilation ECL confirmed that all the highly mobile VB holes generated via electrochemical oxidation at different potentials could be rapidly re-localized by Cu+ to form Cu2+ defects and then couple with electrochemically injected CB electrons for near-infrared ECL of the same excited states. Coreactant ECL demonstrated that simultaneously injecting VB holes and CB electrons into CIS NCs could improve their radiative charge transfer efficiency for efficient ECL. The CIS NCs are promising electrochemiluminophores; ECL provides an effective alternative for investigating radiative charge transfer in CIS NCs upon photoexcitation.

•A spectrum-based ECL immunoassay was developed for determining PSA in NIR region.•The ECL immunoassay demonstrated desired sensitivity and color-selectivity.•The ECL immunoassay might open a way for multiple-colored ECL analysis.The conventional electrochemiluminescence (ECL) analyses were performed via detecting the time (or potential) dependent ECL intensity with the proceeding of ECL reaction. Herein, by spectrally recording all the photons generated in ECL process, a spectral ECL immunoassay was developed in near-infrared (NIR) region with human prostate specific antigen (PSA) as target and dual-stabilizers-capped CdTe nanocrystals (NCs) as tags. The CdTe NCs displayed efficient ECL around 780 nm with the full width at half-maximum around 70 nm in the immune-complexes, the maximum intensity on ECL spectrum profiles increased linearly with the logarithmic increased concentration of PSA from 20.0 fg/mL to 100.0 pg/mL, indicating a sensitive and color-selective ECL immunoassay in NIR region with improved anti-interference performance to biological autofluorescence and tissue absorption. The spectral ECL immunoassay in NIR region might provide an important technique support for developing color-selective ECL assay of different wavebands.

Biorelated single-molecule detection (SMD) has been achieved typically by imaging the redox fluorescent labels and then determining each label one by one. Herein, we demonstrated that the capping agents (i.e., mercaptopropionic acid and sodium hexametaphosphate) can facilitate the electrochemical involved hole (or electron) injecting process and improve the stability of the dual-stabilizers-capped CdSe nanocrystals (NCs), so that the CdSe NCs could be electrochemically and repeatedly inspired to excited states by giving off electrochemiluminescence (ECL) in a cyclic pattern. With the CdSe NCs as ECL label and carcinoembryonic antigen (CEA) as target molecule, a convenient single-molecule immunoassay was proposed by simply detecting the ECL intensity of the dual-stabilizers-capped CdSe NCs in a sandwich-typed immune complex. The limit of detection is 0.10 fg/mL at S/N = 3, which corresponds to about 6–8 CEA molecules in 20 μL of serum sample. Importantly, the ECL spectra of both CdSe NCs and its conjugate with probe antigen in the immune complex were almost identical to the photoluminescence spectrum of bare CdSe NCs, indicating that all emissions were originated from the same excited species. The molecular-counting-free and ECL-based SMD might be a promising alternative to the fluorescent SMD.

Conventional electrochemiluminescence (ECL) research has been performed by detecting the total photons (i.e., the ECL intensity). Herein, systematic spectral exploration on the ECL of dual-stabilizers-capped ternary CdZnSe nanocrystals (NCs) and its sensing application were carried out on a homemade ECL spectral acquiring system. The ternary CdZnSe NCs could be repeatedly injected with electrons via some electrochemical ways and then result in strong cathodic ECL with the coupling of ammonium persulfate. ECL spectrum of the CdZnSe NCs was almost identical to corresponding photoluminescence spectrum, indicating that the excited states of CdZnSe NCs in ECL were essentially the same as those in photoluminescence. Importantly, after being labeled to the probe antibody (Ab2) of α-fetal protein (AFP) antigen, the ternary NCs in the Ab2|NCs conjugates could preserve their ECL spectrum very well. A spectrum-based ECL immunoassay was consequently proposed with the CdZnSe NCs as ECL tags and AFP as target molecules. The limit of detection is 0.010 pg/mL, with a signal-to-noise (S/N) ratio of 3, indicating a sensitive ECL sensing strategy that was different from the conventional ones. This work might open a pathway to the spectrally resolved ECL analysis with even-higher S/N ratios than the fluorescent analysis.

•Eye-visible monochromatic electrochemiluminescence composite film was proposed.•Carbon nanotube and Nafion enhance the sensitivity and lower triggering potential.•Ascorbic acid in serum samples was detected with a limit of detection of 5 pM.•Activity of alkaline phosphatase was detected at the level of 1 μU/L.Sensitive and selective determining bio-related molecule and enzyme play an important role in designing novel procedure for biological sensing and clinical diagnosis. Herein, we found that dual-stabilizers-capped CdSe quantum dots (QDs) in composite film of multi-walled carbon nanotubes (CNTs) and Nafion, displaying eye-visible monochromatic electrochemiluminescence (ECL) with fwhm of 37 nm, which offers promising ECL signal for detecting ascorbic acid (AA) as well as the activity of alkaline phosphatase (ALP) in biological samples. It was also shown that the dual-stabilizers-capped CdSe QDs can preserve their highly passivated surface states with prolonged lifetime of excited states in Nafion mixtures, and facilitate electron-transfer ability of Nafion film along with CNTs. Compared with the QDs/GCE, the ECL intensity is enhanced 1.8 times and triggering potential shifted to lower energy by 0.12 V on the CdSe-CNTs-Nafion/GCE. The ECL quenching degree increases with increasing concentration of AA in the range of 0.01–30 nM with a limit of detection (LOD) of 5 pM. The activity of ALP was determined indirectly according to the concentration of AA, generated in the hydrolysis reaction of l-ascorbic acid 2-phosphate sesquimagnesium (AA-P) in the presence of ALP as a catalyst, with an LOD of 1 μU/L. The proposed strategy is favorable for developing simple ECL sensor or device with high sensitivity, spectral resolution and less electrochemical interference.

•Ultrasensitive sandwich-type immunosensor was developed for the detection of TSGF.•rGO-TEPA added loading capacity of Ab1 and facilitated electron transferability.•Ag-CeO2 nanocomposite facilitated the catalytic reduction of H2O2.•The immunosensor exhibited an extremely low detection limit of 0.2 pg/mL for TSGF.In this paper, an ultrasensitive electrochemical immunosensor was developed for the detection of tumor specific growth factor (TSGF). Reduced graphene oxide-tetraethylene pentamine (rGO-TEPA) was used to modify the surface of glassy carbon electrode (GCE). Meanwhile, Ag@CeO2 nanocomposite was synthesized and applied as secondary-antibody (Ab2) labels for the fabrication of the immunosensor. The amperometric response of the immunosensor for the reduction of H2O2 was recorded. Simultaneously, electrochemical impedance spectroscopy (EIS) and Cyclic voltammetry (CV) were used to characterize the fabrication process of the immunosensor. The anti-TSGF primary antibody (Ab1) was immobilized onto the rGO-TEPA modified GCE via cross-linking with glutaraldehyde (GA). And then the TSGF antigen and Ab2-Ag@CeO2 were modified onto the electrode surface in sequence. Under the optimal conditions, the immunosensor exhibited a wide linear range (0.500–100 pg/mL), a low detection limit (0.2 pg/mL), good reproducibility, acceptable selectivity and excellent stability. The proposed sensing strategy may provide a potential application in the detection of other cancer biomarkers.

A promising electrochemiluminescence (ECL) sensing strategy was proposed with dual-stabilizers-capped CdSe quantum dots (QDs) as ECL emitters. The dual-stabilizers-capped CdSe QDs were covalently immobilized onto p-aminobenzoic acid modified glass carbon electrode with ethylenediamine as a link molecule. This strategy can preserve the completely passivated surface states of dual-stabilizers-capped CdSe QDs, so that the sensor demonstrated eye-visible greenish, band gap engineering and monochromatic ECL emission at 546 nm with a fwhm of 35 nm. Moreover, the proposed sensor could accurately quantify dopamine from 10.0 nM to 3.0 μM with a detection limit of 3.0 nM in practical drug, human urine, and cerebrospinal fluid samples without any signal amplification techniques. This strategy is promising for developing ECL sensors with high sensitivity and spectral selectivity.

•A dual-stabilizers-capped strategy was developed for synthesizing CdSe nanocrystals (NCs) as efficient electrochemiluminescence (ECL) emitters.•The dual-stabilizers-capped CdSe NCs demonstrated bandgap engineered and monochromatic ECL emission.•The ECL of dual-stabilizers-capped CdSe NCs displayed acceptable accuracy and precision for dopamine detection.The development of electrochemiluminescence (ECL) emitters over a broad spectrum of wavelengths is anticipated for the multiplexed ECL sensing and diagnostic application. Herein, a facile dual-stabilizers-capped strategy was developed for synthesizing a series of water-soluble CdSe nanocrystals (NCs) with strong, bandgap engineered and monochromatic ECL emissions in greenish region. The linkage of surface cadmium atoms to the dual stabilizers, mercaptopropionic acid and sodium hexametaphosphate, not only can effectively remove the nonradiative surface state and deep surface trap of CdSe NCs for improved ECL efficiency and monochromaticity, but is also favorable for the electrochemical involved electron and hole injection processes for higher ECL intensity. ECL spectra of dual-stabilizers-capped CdSe NCs are narrow and much close to corresponding photoluminescence spectra, which indicates a series of bandgap engineered and monochromatic ECL emitters. The ECL signal of dual-stabilizers-capped CdSe NCs also shows acceptable accuracy and precision for the detection of dopamine concentration in the practical drug (dopamine hydrochloride injection).

A sandwich-typed near-infrared (NIR) electrochemiluminescence (ECL) immunoassay was developed with dual-stabilizer-capped CdTe nanocrystals (NCs) as ECL labels and α fetoprotein antigen (AFP) as model protein. The dual-stabilizer-capped NIR CdTe NCs were promising ECL labels because of their NIR ECL emission of 800 nm, low anodic ECL potential of +0.85 V, and high biocompatibity, which can facilitate interference-free and highly sensitive ECL bioassays. Upon the immunorecognition of the immobilized AFP to its antibody labeled with dual-stabilizer-capped CdTe NCs, the proposed immunoassay displayed increasing ECL intensity, leading to a wide calibration range of 10.0 pg/mL to 80.0 ng/mL with a detection limit of 5.0 pg/mL [signal-to-noise ratio (S/N) = 3] without coupling any signal amplification procedures. The NIR ECL immunoassay for real samples displayed very similar results with those of Ru(bpy)32+ reagent kit based commercial ECL immunoassay, which not only proved for the efficiency of NIR ECL from dual-stabilizer-capped CdTe NCs but also paved the road for development of novel ECL emitters and corresponding reagent kits.

Anodic near-infrared electrochemiluminescence (ECL) from CdTe quantum dots was achieved at low potential on a glass carbon electrode and a strategy for greatly enhanced band-gap ECL was presented.

We developed an ultrasensitive electrochemiluminescence (ECL) method for DNA determination using magnetic submicrobeads (SMBs) as the carrier of Ru(bpy)32+ (bpy = 2,2′-bipyridy) and carbon nanotubes (CNTs) as accessorial electrode material. The SMBs with Ru(bpy)32+ were wrapped with CNTs and then immobilized on an Au electrode. In the presence of tri-n-propylamine, ECL of the Ru(bpy)32+ on the SMBs was detected. Since one target DNA (t-DNA) molecule corresponded to one SMB with a large number of Ru(bpy)32+, the ECL signal was amplified. In addition, the Ru(bpy)32+-loaded SMBs were wrapped with CNTs that contacted the electrode. The ECL of Ru(bpy)32+ was greatly increased. Using this method, t-DNA of 3 × 10−16 mol/L could be detected. The method could be used to quantify mRNA in cells.Highlights► Electrochemiluminescence (ECL) of Ru(bpy)32+-coated submicrobeads wrapped with carbon nanotubes is measured. ► Ultrasensitive ECL method for determination of 3 × 10−16 mol/L DNA is investigated. ► The ECL method is used to quantify mRNA in cells.

The electrochemistry of mercaptopropionic acid capped CdTe quantum dots (QDs) was studied by differential pulse voltammetry, three processes were obtained at 0.36 (A1), 0.68 (A2) and 0.84 V (A3), respectively. A1 process could be selectively suppressed by magnesium ion, an electrochemical sensor for magnesium ion was developed with a linear response from 4 × 10−5 to 1 × 10−2 mol/L and good reproducibility. This electrochemical sensing application of QDs may provide a new strategy for QDs-based detection.

Anodic near-infrared electrochemiluminescence (ECL) from CdTe quantum dots was achieved at low potential on a glass carbon electrode and a strategy for greatly enhanced band-gap ECL was presented.