An aptamer-binding DNA walking machine for sensitive electrochemiluminescence detection of tumor exosomes.

An aptamer-binding DNA walking machine triggered by the recognition of aptamers to exosomes was firstly reported for sensitive electrochemiluminescence (ECL) detection of exosomes.

A surface-confined DNA assembly amplification strategy on DNA nanostructural scaffold for electrochemiluminescence biosensing.

A critical challenge in surface-based DNA assembly amplification is the reduced accessibility of DNA strands arranged on a heterogeneous surface compared to that in homogeneous solution. Here, a novel in situ surface-confined DNA assembly amplification electrochemiluminescence (ECL) biosensor based on DNA nanostructural scaffold was presented. In this design, a stem-loop structural DNA segment (Hairpin 1) was constructed on the vertex of DNA nanostructural scaffold as recognition probe. In the present of target DNA, the hairpin structure changed to rod-like through complementary hybridization with target DNA, resulting in the formation of Hairpin 1:target DNA. When the obtained Hairpin 1:target DNA met Hairpin 2 labeled with glucose oxidase (GOD), the DNA cyclic amplification was activated, releasing target DNA into homogeneous solution for the next recycling. Thus, the ECL signal of Ru(bpy)32+-TPrA system was quenched by H2O2, the product of GOD catalyzing glucose. As a result, this proposed method achieved a linear range response from 50 aM to 10 pM with lower detection limit of 20 aM.

Plasmon-Enhanced Electrochemiluminescence for Nucleic Acid Detection Based on Gold Nanodendrites.

Gold nanodendrites (Au NDs) exhibit extremely strong electromagnetic field located around multiple tip branches due to a plasmon coupling effect. In this work, a novel LSPR-enhanced ECL emission from CdTe nanocrystals (NCs) by Au NDs for the detection of nucleic acid is reported. This system is composed of a thin film of CdTe NCs on glassy carbon electrode (GCE) as anodic ECL emitter and Au NDs as plasmon enhancer. DNA tetrahedron embedded with a stem-loop hairpin structure on one edge was applied as a switch to regulate the distance between CdTe NCs and Au NDs. At original state, the hairpin structure was closed and DNA tetrahedron played in a relaxed state on CdTe NCs film. The ECL emission of CdTe NCs was quenched by proximal Au NDs due to Förster resonance energy transfer (FRET), which was defined as the "turn-off" mode. After the complementary hybridization with target DNA, the hairpin structure changed to a rodlike configuration, resulting in an increased distance between CdTe NCs and Au NDs, and a significant enhancement of ECL induced by LSPR of Au NDs, which was defined as a "turn-on" mode. Along with the asymmetric modification method, a controllable and versatile pathway for modifying nanomaterials, the ECL sensor performed well with great stability and repeatability for nucleic acid detection in the range from 1.0 to 500 fM. Considering the high sensitivity and selectivity in the serum sample assay, this proposed method indicates a great potential for bioassay application.

Self-Assembled DNA Tetrahedral Scaffolds for the Construction of Electrochemiluminescence Biosensor with Programmable DNA Cyclic Amplification.

A novel DNA tetrahedron-structured electrochemiluminescence (ECL) platform for bioanalysis with programmable DNA cyclic amplification was developed. In this work, glucose oxidase (GOD) was labeled to a DNA sequence (S) as functional conjugation (GOD-S), which could hybridize with other DNA sequences (L and P) to form GOD-S:L:P probe. In the presence of target DNA and a help DNA (A), the programmable DNA cyclic amplification was activated and released GOD-S via toehold-mediated strand displacement. Then, the obtained GOD-S was further immobilized on the DNA tetrahedral scaffolds with a pendant capture DNA and Ru(bpy)32+-conjugated silica nanoparticles (RuSi NPs) decorated on the electrode surface. Thus, the amount of GOD-S assembled on the electrode surface depended on the concentration of target DNA and GOD could catalyze glucose to generate H2O2 in situ. The ECL signal of Ru(bpy)32+-TPrA system was quenched by the presence of H2O2. By integrating the programmable DNA cyclic amplification and in situ generating H2O2 as Ru(bpy)32+ ECL quencher, a sensitive DNA tetrahedron-structured ECL sensing platform was proposed for DNA detection. Under optimized conditions, this biosensor showed a wide linear range from 100 aM to 10 pM with a detection limit of 40 aM, indicating a promising application in DNA analysis. Furthermore, by labeling GOD to different recognition elements, the proposed strategy could be used for the detection of various targets. Thus, this programmable cascade amplification strategy not only retains the high selectivity and good capturing efficiency of tetrahedral-decorated electrode surface but also provides potential applications in the construction of ECL biosensor.

DNA tetrahedral scaffolds-based platform for the construction of electrochemiluminescence biosensor.

Proximal metallic nanoparticles (NPs) could quench the electrochemiluminescence (ECL) emission of semiconductor quantum dots (QDs) due to Förster energy transfer (FRET), but at a certain distance, the coupling of light-emission with surface plasmon resonance (SPR) result in enhanced ECL. Thus, the modification strategies and distances control between QDs and metallic NPs are critical for the ECL intensity of QDs. In this strategy, a SPR enhanced ECL sensor based on DNA tetrahedral scaffolds modified platform was reported for the detection of telomerase activity. Due to the rigid three-dimensional structure, DNA tetrahedral scaffolds grafting on the electrode surface could accurately modulate the distance between CdS QDs and luminol labelled gold nanoparticles (L-Au NPs), meanwhile provide an enhanced spatial dimension and accessibility for the assembly of multiple L-Au NPs. The ECL intensities of both CdS QDs (-1.25V vs. SCE) and luminol (+0.33V vs. SCE) gradually increased along with the formation of multiple L-Au NPs at the vertex of DNA tetrahedral scaffolds induced by telomerase, bringing in a dual-potential ECL analysis. The proposed method showed high sensitivity for the identification of telomerase and was successfully applied for the differentiation of cancer cells from normal cells. This work suggests that DNA tetrahedral scaffolds could serve as an excellent choice for the construction of SPR-ECL system.

Distance mediated electrochemiluminescence enhancement of CdS thin films induced by the plasmon coupling of gold nanoparticle dimers.

Gold nanoparticle dimers assembled on the surface of CdS QD thin films served as nano-antennas to mediate the distance-dependent plasmon enhanced electrochemiluminescence of QDs.

A novel DNA tetrahedron-hairpin probe for in situ"off-on" fluorescence imaging of intracellular telomerase activity.

A novel three-dimensionally structured DNA probe is reported to realize in situ"off-on" imaging of intracellular telomerase activity. The probe consists of a DNA tetrahedron and a hairpin DNA on one of the vertices of the DNA tetrahedron. It is composed of four modified DNA segments: S1-Au nanoparticle (NP) inserting a telomerase strand primer (TSP) and S2-S4, three Cy5 dye modified DNA segments. Fluorescence of Cy5 at three vertices of the DNA tetrahedron is quenched by the Au NP at the other vertex due to the effective fluorescence resonance energy transfer (FRET) ("off" state). When the probe meets telomerase, the hairpin structure changes to rod-like through complementary hybridization with the telomerase-triggered stem elongation product, resulting in a large distance between the Au NP and Cy5 and the recovery of Cy5 fluorescence ("on" state). The molar ratio of 3 : 1 between the reporter (Cy5) and the target related TSP makes the probe show high sensitivity and recovery efficiency of Cy5 in the presence of telomerase extracted from HeLa cells. Given the functional and compact nanostructure, the mechanically stable and noncytotoxic nature of the DNA tetrahedron, this FRET-based probe provides more opportunities for biosensing, molecular imaging and drug delivery.

A ratiometric electrochemiluminescence detection for cancer cells using g-C3N4 nanosheets and Ag-PAMAM-luminol nanocomposites.

In this work, a dual-signaling electrochemiluminescence (ECL) ratiometric sensing approach for the detection of HL-60 cancer cells was reported for the first time. G-C3N4 nanosheets and Ag-PAMAM-luminol nanocomposits (Ag-PAMAM-luminol NCs) were prepared and served as reductive-oxidative and oxidative-reductive ECL emitters respectively. DNA probe functionalized Ag-PAMAM-luminol NCs would hybridize with aptamers modified onto magnetic beads. In the presence of HL-60 cells, the aptamer would conjugate with the target cell and release Ag-PAMAM-luminol NCs. After magnetic separation, released Ag-PAMAM-luminol NCs would hybridize with capture DNA on g-C3N4 nanosheets. ECL from g-C3N4 nanosheets coated on ITO electrode at -1.25 V (vs SCE) could be quenched by Ag-PAMAM-luminol NCs due to the resonance energy transfer (RET) from g-C3N4 nanosheets to Ag NPs. Meanwhile, Ag-PAMAM-luminol brought the ECL signal of luminol at +0.45 V (vs SCE). Thus, the concentration of HL-60 cancer cells could be quantified by both the quenching of ECL from g-C3N4 nanosheets and the enhancement of ECL from luminol. By measuring the ratio of ECL intensities at two excitation potentials, this approach could achieve sensitive and reliable detection for cancer cells in a wide range from 200 cells/mL to 9000 cells/mL with the detection limit of 150 cells (S/N=3).

Dual-Wavelength Electrochemiluminescence Ratiometry Based on Resonance Energy Transfer between Au Nanoparticles Functionalized g-C3N4 Nanosheet and Ru(bpy)3(2+) for microRNA Detection.

Here, a dual-wavelength ratiometric electrochemiluminescence (ECL) approach is reported based on resonance energy transfer (RET) from graphite-like carbon nitride nanosheet (g-C3N4 NS) to Ru(bpy)3(2+) for sensitive detection of microRNA (miRNA). In this approach, Au nanoparticles (Au NPs) functionalized g-C3N4 NS nanohybrid (Au-g-C3N4 NH) coated on glassy carbon electrode (GCE) could exhibit strong and stable ECL emissions with emission peak centered at 460 nm. The ECL emission at such wavelength matched well with the absorption peak of Ru(bpy)3(2+) as well as impeccably stimulating the emission of Ru(bpy)3(2+) at the wavelength of 620 nm, producing ECL-RET with high efficiency. Thus, based on the ECL signals quenching at 460 nm and increasing at 620 nm, a dual-wavelength ratiometric ECL-RET system was achieved. This system was then utilized for determination of target miRNA. With the attachment of thiol-modified molecular beacon on Au-g-C3N4 NH, target miRNA hybridized with the molecular beacon to form a DNA-RNA duplex. The obtained DNA-RNA duplex could be cleaved by duplex-specific nuclease to release target miRNA which would take part in the next cycle for further hybridization. Finally, the introducing of Ru(bpy)3(2+) was through the probe DNA-Ru(bpy)3(2+) complementary with the rest single-strand DNA on electrode. By measuring the ratio of ECL(460 nm)/ECL(620 nm), we could accurately quantify the concentration of miRNA-21 in a wide range from 1.0 fM to 1.0 nM. This work provides an important reference for the study of dual-wavelength ECL ratiometry and also exhibits potential capability in the detection of nucleic acids.

Silver Nanoclusters for High-Efficiency Quenching of CdS Nanocrystal Electrochemiluminescence and Sensitive Detection of microRNA.

In this work, oligonucleotide-encapusulated silver nanoclusters were applied in the electrochemiluminescence (ECL) system of CdS nanocrystals (NCs)/ K2S2O8 based on dual ECL quenching effects. We found that the ECL emission of CdS NCs matched well with the absorption band of oligonucleotide encapsulated Ag nanoclusters, which could act as the energy acceptor of CdS NCs ECL so as to lead to an effective ECL resonance energy transfer (RET). On the other hand, the Ag nanoclusters could also catalyze electrochemical reduction of K2S2O8, resulting in increased consumption of ECL coreactant near the working electrode and decreased ECL intensity from CdS NCs. On the basis of the dual ECL quenching effects, a sensitive ECL biosensor for detection of microRNA was successfully achieved with a wide linear range from 10 fM to 100 pM.

Visual electrochemiluminescence detection of telomerase activity based on multifunctional Au nanoparticles modified with G-quadruplex deoxyribozyme and luminol.

A novel visual electrochemiluminescence (ECL) analysis strategy for detection of telomerase activity is reported on a microarray chip, with G-quadruplex deoxyribozyme (DNAzyme) and luminol modified Au nanoparticles (NPs) as double-catalytic amplification labels.

Disposable paper-based bipolar electrode for sensitive electrochemiluminescence detection of a cancer biomarker.

A disposable paper-based bipolar electrode (BPE) was reported for the first time for the sensitive electrochemiluminescence detection of a prostate specific antigen (PSA).

Paper-based electroanalytical devices for in situ determination of salicylic acid in living tomato leaves.

Detection of phytohormones in situ has gained significant attention due to their critical roles in regulating developmental processes and signaling for defenses in plants at low concentration. As one type of plant hormones, salicylic acid has recently been found to be one of pivotal signal molecules for physiological behaviors of plants. Here we report the application of paper-based electroanalytical devices for sensitively in situ detection of salicylic acid in tomato leaves with the sample volume of several microliters. Specifically, disposable working electrodes were fabricated by coating carbon tape with the mixture of multiwall carbon nanotubes and nafion. We observed that the treatment of the modified carbon tape electrodes with oxygen plasma could significantly improve electrochemical responses of salicylic acid. The tomato leaves had a punched hole of 1.5mm diameter to release salicylic acid with minor influence on continuous growth of tomatoes. By incorporating the tomato leaf with the paper-based analytical device, we were able to perform in situ determination of salicylic acid based on its electrocatalytic oxidation. Our experimental results demonstrated that the amounts of salicylic acid differed statistically in normal, phytoene desaturase (PDS) gene silent and diseased (infected by Botrytis cinerea) tomato leaves. By quantifying salicylic acid at the level of several nanograms in situ, the simple paper-based electroanalytical devices could potentially facilitate the study of defense mechanism of plants under biotic and abiotic stresses. This study might also provide a sensitive method with spatiotemporal resolution for mapping of chemicals released from living organisms.

Using nanostructured conductive carbon tape modified with bismuth as the disposable working electrode for stripping analysis in paper-based analytical devices.

Low cost disposable working electrodes are specifically desired for practical applications of electrochemical detection considering maturity of electrochemical stations and data collection protocols. In this paper double-sided conductive adhesive carbon tape with nanostructure was applied to fabricate disposable working electrodes. Being supported by indium tin oxide glass, the prepared carbon tape electrodes were coated with bismuth film for stripping analysis of heavy metal ions. By integrating the bismuth modified electrodes with paper-based analytical devices, we were able to differentiate Zn, Cd and Pb ions with the sample volume of around 15 µL. After the optimization of parameters, including modification of bismuth film and the area of the electrodes, etc., Pb ions could be measured in the linear range from 10 to 500 µg/L with the detection limit of 2 µg/L. Our experimental results revealed that the disposable modified electrodes could be used to quantify migrated lead from toys with the results agreed well with that using atomic absorption spectrometry. Although bismuth modification and stripping analysis could be influenced by the low conductivity of the carbon tape, the low cost disposable carbon tape electrodes take the advantages of large-scaled produced double-sided carbon tape, including its reproducible nanostructure and scaled-up fabrication process. In addition, the preparation of disposable electrodes avoids time-consuming pretreatment and experienced operation. This study implied that the carbon tape might be an alternative candidate for practical applications of electrochemical detection.