Guizheng Zou

A Monochromatic Electrochemiluminescence Sensing Strategy for Dopamine with Dual-Stabilizers-Capped CdSe Quantum Dots as Emitters

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.

Ultrasensitive Immunoassay Based on Anodic Near-Infrared Electrochemiluminescence from Dual-Stabilizer-Capped CdTe Nanocrystals

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)(3)(2+) 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.

Ultrasensitive Electrochemical DNA Assay Based on Counting of Single Magnetic Nanobeads by a Combination of DNA Amplification and Enzyme Amplification

An ultrasensitive electrochemical method for determination of DNA is developed based on counting of single magnetic nanobeads (MNBs) corresponding to single DNA sequences combined with a double amplification (DNA amplification and enzyme amplification). In this method, target DNA (t-DNA) is captured on a streptavidin-coated substrate via biotinylated capture DNA. Then, MNBs functionalized with first-probe DNAs (p1-DNA-MNBs) are conjugated to t-DNA sequences with a ratio of 1:1. Subsequently, the p1-DNA-MNBs are released from the substrate via dehybridization. The released p1-DNA-MNBs are labeled with alkaline phosphatase (AP) using biotinylated second-probe DNAs (p2-DNAs) and streptavidin-AP conjugates. The resultant AP-p2-DNA-p1-DNA-MNBs with enzyme substrate disodium phenyl phosphate (DPP) are continuously introduced through a capillary as the microsampler and microreactor at 40 degrees C. AP on the AP-p2-DNA-p1-DNA-MNBs converts a huge number of DPP into its product phenol, and phenol zones are produced around each moving AP-p2-DNA-p1-DNA-MNB. The phenol zones are continuously delivered to the capillary outlet and detected by a carbon fiber disk bundle electrode at 1.05 V. An elution curve with peaks is obtained. Each peak is corresponding to a phenol zone relative to single t-DNA sequence. The peaks on the elution curve are counted for quantification. The number of the peaks is proportional to the concentration of t-DNA in a range of 5.0 x 10(-16) to 1.0 x 10(-13) mol/L.

Quantitative counting of single fluorescent molecules by combined electrochemical adsorption accumulation and total internal reflection fluorescence microscopy.

We developed an ultrasensitive quantitative single-molecule imaging method for fluorescent molecules using a combination of electrochemical adsorption accumulation and total internal reflection fluorescence microscopy (TIRFM). We chose rhodamine 6G (R6G, fluorescence dye) or goat anti-rat IgG(H+L) (IgG(H+L)-488), a protein labeled by Alexa Fluor 488 or DNA labeled by 6- CR6G (DNA-R6G) as the model molecules. The fluorescent molecules were accumulated on a light transparent indium tin oxide (ITO) conductive microscope coverslip using electrochemical adsorption in a stirred solution. Then, images of the fluorescent molecules accumulated on the ITO coverslip sized 40 x 40 microm were acquired using an objective-type TIRFM instrument coupled with a high-sensitivity electron multiplying charge-coupled device. One hundred images of the fluorescent molecules accumulated on the coverslip were taken consecutively, one by one, by moving the coverslip with the aid of a three-dimensional positioner. Finally, we counted the number of fluorescent spots corresponding to single fluorescent molecules on the images. The linear relationships between the number of fluorescent molecules and the concentration were obtained in the range of 5 x 10(-15) to 5 x 10(-12) mol/L for R6G, 3 x 10(-15) to 2 x 10(-12) mol/L for IgG(H+L)-488, and 3 x 10(-15) to 2 x 10(-12) mol/L for DNA-R6G.

Molecular-Counting-Free and Electrochemiluminescent Single-Molecule Immunoassay with Dual-Stabilizers-Capped CdSe Nanocrystals as Labels

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.

Spectrum-Based Electrochemiluminescent Immunoassay with Ternary CdZnSe Nanocrystals as Labels

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.

Bandgap engineered and high monochromatic electrochemiluminescence from dual-stabilizers-capped CdSe nanocrystals with practical application potential.

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).

Electrochemistry and Electrochemiluminescence of Organometal Halide Perovskite Nanocrystals in Aqueous Medium

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.

Spectrum-based and color-selective electrochemiluminescence immunoassay for determining human prostate specific antigen in near-infrared region

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 780nm with the full width at half-maximum around 70nm in the immune-complexes, the maximum intensity on ECL spectrum profiles increased linearly with the logarithmic increased concentration of PSA from 20.0fg/mL to 100.0pg/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.

Sensitive and selective determining ascorbic acid and activity of alkaline phosphatase based on electrochemiluminescence of dual-stabilizers-capped CdSe quantum dots in carbon nanotube-nafion composite.

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 37nm, 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 0.12V on the CdSe-CNTs-Nafion/GCE. The ECL quenching degree increases with increasing concentration of AA in the range of 0.01-30nM with a limit of detection (LOD) of 5pM. 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 1μU/L. The proposed strategy is favorable for developing simple ECL sensor or device with high sensitivity, spectral resolution and less electrochemical interference.