Highly-efficient luminol immobilization approach and exponential strand displacement reaction based electrochemiluminescent strategy for monitoring microRNA expression in cell.

This work used 3,4,9,10-perylenetetracarboxylic acid-luminol composite (PTCA-luminol) as signal tag with improved ECL signal and applied cruciform DNA structure mediated exponential strand displacement reaction (SDR) to construct an ultrasensitive electrochemiluminescence (ECL) biosensor for microRNA-21 (miRNA-21) detection. The novel luminol-based signal tags was synthesized utilizing the π-π stacking interaction between PTCA and luminol, realizing highly effective and stable immobilization of luminol and resulting in good stability and strong ECL response. Meanwhile, target miRNA-21 triggered disaggregation of cruciform DNA structure was used to mediate exponential SDR for target recycling amplification. Taking advantage of the novel luminol-based signal tag and exponential SDR, the proposed ECL biosensor achieved excellent sensitivity with wide linear range from 10 aM to 100 pM and detection limit was 2 aM. Moreover, this ECL biosensor was applied to estimate the expression level of miRNA-21 and pharmacodynamics of matrine in human breast cancer cells (MCF-7 cells). The proposed biosensor provided a new opportunity for the preparation of ECL nanomaterials and exhibited great application potential in other biomarkers detection, clinical application and pharmacodynamics evaluation.

Novel Ru(bpy)2(cpaphen)2+/TPrA/TiO2 Ternary ECL System: An Efficient Platform for the Detection of Glutathione with Mn2+ as Substitute Target.

A sensitive electrochemiluminescence (ECL) biosensor was developed for glutathione (GSH) detection based on a novel Ru(bpy)2(cpaphen)2+/TPrA/TiO2 ternary ECL system with Mn2+ as substitute target for signal amplification. Specifically, the TiO2 nanoneedles (TiO2 NNs) were used as the coreaction accelerator for the first time to promote the oxidation process of coreactant tripropylamine (TPrA) in the anode and significantly increase the ECL signal of Ru(bpy)2(cpaphen)2+ for an amplified initial signal. Meanwhile, a novel target conversion strategy for GSH was developed by reducing MnO2 nanosheets to Mn2+ as a substitute target, which played the role of a coenzyme factor for cleaving DNA double strands intercalated with Ru(bpy)2(cpaphen)2+ to markedly weaken initial signal. As a result, the novel "on-off" biosensor achieved a sensitive detection of GSH range from 5 µM to 215 µM with a detection limit of 0.33 µM. Importantly, the proposed strategy enriched the application of Ru complex and TPrA ECL system in bioanalytical applications, and provided a new signal amplification strategy for bioactive small molecules.

Efficient Electrochemical Self-Catalytic Platform Based on l-Cys-hemin/G-quadruplex and Its Application for Bioassay.

Commonly, in the artificial enzyme-involved signal amplification approach, the catalytic efficiency was limited by the relatively low binding affinity between artificial enzyme and substrate. In this work, substrate l-cysteine (l-Cys) and hemin were combined into one molecule to form l-Cys-hemin/G-quadruplex as an artificial self-catalytic complex for the improvement of the binding affinity between l-Cys-hemin/G-quadruplex and l-Cys. The apparent Michaelis-Menten constant ( Km = 2.615 µM) on l-Cys-hemin/G-quadruplex for l-Cys was further investigated to assess the affinity, which was much lower than that of hemin/G-quadruplex ( Km = 8.640 µM), confirming l-Cys-hemin/G-quadruplex possessed better affinity to l-Cys compared with that of hemin/G-quadruplex. Meanwhile, l-Cys bilayer could be further assembled onto the surface of l-Cys-hemin/G-quadruplex based on hydrogen-bond and electrostatic interaction to concentrate l-Cys around the active center, which was beneficial to the catalytic enhancement. Through this efficient electrochemical self-catalytic platform, a sensitive thrombin aptasensor was constructed. The results exhibited good sensitivity from 0.1 pM to 80 nM and the detection limit was calculated to be 0.032 pM. This self-catalytic strategy with improved binding affinity between l-Cys-hemin/G-quadruplex and l-Cys could provide an efficient approach to improve artificial enzymatic catalytic efficiency.

Enzyme-free Target Recycling and Double-Output Amplification System for Electrochemiluminescent Assay of Mucin 1 with MoS2 Nanoflowers as Co-reaction Accelerator.

In this work, a sensitive electrochemiluminescent assay of mucin 1 (MUC1) was developed with the advantages of target recycling amplification strategy and effective MoS2 nanoflower (MoS2 NF)-based signal probe. Briefly, the target MUC1 triggered enzyme-free recycling and a double-output amplification process was executed to acquire masses of single-stranded DNA as a mimic target, which further participated in the catalytic hairpin assembly process for signal amplification. Meanwhile, MoS2 NFs were prepared as an effective co-reaction accelerator, which not only possessed excellent catalytic performance for H2O2 decomposition to largely enhance the luminous intensity of N-(aminobutyl)- N-(ethylisoluminol) (ABEI)-H2O2 electrochemiluminescence system but also offered a desirable platform for ABEI-functionalized Ag nanoparticles (ABEI-Ag complexes) loading via Ag-S binding. The experimental results showed the proposed aptasensor had a good linear relationship in the range of 1 fg/mL to 10 ng/mL for MUC1 detection and the limit of detection was 0.58 fg/mL (S/N = 3). In addition, the aptasensor had nice stability and selectivity and huge potential to be applied in clinical research.

In situ generation of electrochemiluminescent DNA nanoflowers as a signal tag for mucin 1 detection based on a strategy of target and mimic target synchronous cycling amplification.

A sensitive electrochemiluminescent (ECL) aptasensor consisting of a novel ECL signal tag of DNA nanoflowers (DNA NFs) and a highly efficient target conversion strategy for the MUC1 assay was developed, which not only increased the stability for luminophore loading, but also greatly improved the detection sensitivity.

MoS2 Quantum Dots as New Electrochemiluminescence Emitters for Ultrasensitive Bioanalysis of Lipopolysaccharide.

Cd-based semiconductor quantum dots (QDs) with size-tunable luminescence and high quantum yield have become the most promising electrochemiluminescence (ECL) emitters. However, their unavoidable biotoxicity limited their applications in bioassays. Here, the nontoxic and economical MoS2 QDs prepared by chemical exfoliation from the bulk MoS2 were first investigated as new ECL emitters, and then the possible luminescence mechanism of MoS2 QDs was studied using ECL-potential curves and differential pulse voltammetry (DPV) methods in detail. With MoS2 QDs as the ECL emitters and triethylamine (TEA) as the efficient coreactant, a practical and label-free aptasensor for lipopolysaccharide (LPS) detection was constructed based on aptamer recognition-driven target-cycling synchronized rolling circle amplification. Comparing to conventional stepwise reactions, this target-cycling synchronized rolling circle amplification achieved more efficient signal amplification and simpler operation. The developed assay for LPS detection demonstrated a wide linear range of 0.1 fg/mL to 50 ng/mL with limit of detection down to 0.07 fg/mL. It is worth mentioning that MoS2 QDs with stable ECL emission exhibited a great application potential in ECL bioanalysis and imaging as a new type of excellent emitter candidates.

Cu Nanoclusters: Novel Electrochemiluminescence Emitters for Bioanalysis.

Cu nanoclusters (Cu NCs), which emerged as a new class of nontoxic, economic, and excellent phosphors and catalysts, have attracted increasing interest for a wide variety of promising applications in biolabeling and biocatalysis. However, the electrochemiluminescence (ECL) behavior of Cu NCs has never been reported in previous works. Here, anodic and blue ECL emission of Cu NCs was observed for the first time with the efficient coreactant of hydrazine (HZ), and the possible luminescence mechanism of Cu NCs/HZ ECL system was studied in detail. Briefly, HZ was oxidized, and Cu NCs got the energy to generate excited state Cu NCs* for light radiation. Furthermore, a highly sensitive "signal-off" sensing platform for the determination of dopamine has been developed upon effectively quenching of dopamine toward the Cu NCs/HZ-based ECL system. As a result, this proposed method for dopamine detection possesses high selectivity, good stability, and excellent sensitivity with a detection limit down to 3.5 × 10-13 M. This indicates that Cu NCs show potential for applications in ECL bioanalysis as a new type of low-cost and superior luminophore candidates.