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• A novel dual engine-triggered DNA walker was elaborated based on precise orientation protocol. • The DNA cubes were used as the scaffold for anchoring the dual swing arms and tracks as signal switches. • The electrochemiluminescence (ECL) molecule perylene doped-titanium dioxide (Pe-TiO 2) nanospheres with low cost and high reproducibility were synthesized by one-step sol–gel method. • The proposed biosensor based on Pe-TiO 2 nanospheres realized ultrasensitive detection of microRNA let-7a. Despite the intrinsic programmability and flexible biological functions of DNA walkers, it remains challenging for traditional DNA walkers to precisely control mechanical running paths in nanoscale spaces. In this work, an elegant dual engine-triggered DNA walker was elaborated based on precise orientation protocol, applying the DNA cube as the scaffold for anchoring the dual swing arms as engines and tracks as signal switches. The order arrangement and dual engines enhanced the operating efficiency and controllability of the DNA walker markedly. Moreover, the electrochemiluminescence (ECL) molecule perylene doped-titanium dioxide (Pe-TiO 2) organic–inorganic nanospheres with low cost and high reproducibility were synthesized as the ECL emitters by one-step sol–gel method. It was worth noting that TiO 2 gel not only restricted the stacking mode of Pe molecules in vibration and rotation, but also enhanced the interfacial charge transfer ability in organic–inorganic hybrid mode, resulting in the improvement of ECL efficiency and structural stability. Based on the luminous Pe-TiO 2 nanospheres, a ternary ECL system was proposed with S 2 O 8 2− as coreactant, and silver nanoparticles (Ag NPs) as coreaction accelerator. Ultimately, by combing the dual engine-triggered DNA walker with the ternary ECL system, an efficient ECL bioassay platform was developed for microRNA let 7a (let-7a) detection with a wide linear range from 10 fmol/L to 100 nmol/L and a low detection limit of 7.0 fmol/L. Hence, this work offered a universal strategy to predesign walking paths and improve loading capacity in virtue of DNA nanostructures, as well as to expand the biology research of planar organic luminophores in an organic–inorganic hybrid manner. [ABSTRACT FROM AUTHOR]

Herein, the microRNA-141 electrochemiluminescence (ECL) bioassay was developed using the dual-ligand metal-organic framework (d-MOF) with ordered heterogeneity, which simultaneously contained the luminophore ligands (1,1,2,2-tetra(4-carboxylbiphenyl)ethylene, denoted as TCBPE) and the coreactant ligands (1,4-diazabicyclo[2.2.2]octane, denoted as DN 2 H 2). The resultant d-MOF revealed significantly enhanced ECL intensity without any exogenous coreactants, which was 3.53 times higher in comparison with that of single-ligand MOF (only TCBPE as ligands) even with the addition of exogenous DN 2 H 2. Thanks to the ordered heterogeneity in d-MOF, the intramolecular rotation of TCBPE was restricted via oriented coordination and the spatial location of DN 2 H 2 was reasonably arranged due to the framework structure, which could not only enhance the excitation efficiency but also improve the electron-transfer efficiency based on the synergistic enhancement effect between structures and compositions in micro/nano confined space. Based on this, the proposed biosensor employed a novel DNA triangular prism (DNA TP) as signal switch to detect microRNA-141, achieving the low detection limit at the level of 22.9 aM and a broad linear ranging from 100 aM to 100 pM. The precise design of the ordered d-MOFs by co-assembling the luminophore and coreactant ligands holds a promise strategy to achieve ECL MOFs and construct the ECL biosensors in diagnostic analysis. [ABSTRACT FROM AUTHOR]

An electrochemiluminescence (ECL) immunoassay protocol was developed based on mimic-intramolecular interaction for sensitive detection of prostate specific antigen (PSA). It was constructed by integrating the ECL luminophore (tris(4,4′-dicarboxylicacid-2,2′-bipyridyl)-ruthenium(ii)dichloride (Ru(dcbpy)32+)) and coreactant (histidine) into the supersandwich DNA structure. This strategy was more effective in amplifying the ECL signal by shortening the electronic transmission distance, improving the ECL luminous stability and enhancing the ECL luminous efficiency. The ECL matrices denoted as MWCNTs@PDA–AuNPs were fabricated through spontaneous oxidative polymerization of dopamine (DA) on multiwalled carbon nanotubes (MWCNTs) and reducing HAuCl4 to produce gold nanoparticles (AuNPs) by DA simultaneously. Then, the prepared matrices were applied to bind capture antibodies. Moreover, supersandwich Ab2 bioconjugate was designed using a PAMAM dendrimer to immobilize the detection antibody and supersandwich DNA structure. The PAMAM dendrimer, with a plurality of secondary and tertiary amine groups, not only facilitated high-density immobilization of the detection antibody and supersandwich DNA structure, but also greatly amplified the ECL signal of Ru(dcbpy)32+. The supersandwich DNA structure contained multiple Ru(dcbpy)32+ and histidine, further amplifying the ECL signal. The proposed supersandwich immunosensor showed high sensitivity with a detection limit of 4.2 fg mL−1 and a wide linear range of 0.01 pg mL−1–40.00 ng mL−1. With the excellent stability, satisfying precision and reproducibility, the proposed immunosensor indicates promising practicability for clinical diagnosis. [ABSTRACT FROM AUTHOR]

A dual signal amplification strategy was designed to construct a cathodic peroxydisulfate-based electrochemiluminescence (ECL) aptasensor for the ultrasensitive detection of thrombin (TB) as a model analyte. The signal was amplified by the employment of two kinds of co-reactant, (1) in situ generated dissolved O2 from the cascade catalysis of GOD and HRP as co-reactants and (2) intercalation of a new co-reactant into the grooves of the dsDNA polymers based on the hybridization chain reaction (HCR). Femtomolar levels of TB could be detected using the developed aptasensor, with high sensitivity and good stability. Thus the S2O82−–O2 ECL system has great potential for development and application in clinical diagnostics, immunology and biomedical research. [ABSTRACT FROM AUTHOR]

Abstract: This work described the construction of a reagentless and ultrasensitive electrochemiluminescence (ECL) immunosensor using poly-l-lysine as a co-reactant with for signal amplification and magnetic Fe3O4 loaded graphene nanosheet as nanoprobes, which can achieve an impressive detection limit of 0.03pg/mL human total 3,3′,5-triiodothyronine (T3), a kind of diagnostic markers of thyroid disease. The bionanoprobes were prepared based on the coimmobilization of and T3 detection antibody on the Fe3O4 loaded graphene nanosheet and the sensing interface was achieved by assembling T3 capture antibody on the gold nanoparticles (AuNPs) loaded electro-deposited l-lysine film modified bare glass carbon electrode (GCE). ECL responses were generated from the modified electrodes described above by just immersing them in phosphate buffer solutions (PBS) based on the sandwich-type immunoreactions. T3 was measured quantitatively in the range from 0.1pg/mL to 10ng/mL, which exhibits sufficiently high sensitivity and stability. The reagentless ECL immunoassay is a promising approach for the detection of a wide range of molecular analytes. [Copyright &y& Elsevier]

In this work, a new signal amplified strategy based on the quenching effect of hemin and Au nanoparticles decorated CeO 2 nanoparticles (Au@CeO 2 NPs) for ultrasensitive detection of thrombin (TB) is reported for the first time. Herein, the poly(ethylenimine) (PEI) enhanced Ru(bpy) 3 2+ nanocomposite was implemented by direct chemical polymerization, which could provide the desirable enhanced initial ECL signal. Furthermore, the detection aptamer of thrombin (TBA 2) was immobilized on Au@CeO 2 NPs to form TBA 2/Au@CeO 2 conjugates. Then, the G-rich DNA of TBA 2 sequence could fold into a G-quadruplex structure to embed hemin to obtain the quenching probe of hemin/TBA 2/Au@CeO 2 conjugates. In the presence of target TB, the sandwiched structure could be formed between capture aptamer (TBA 1), TB and hemin/TBA 2/Au@CeO 2 conjugates, thereby resulting in a proportional quenching in ECL response with TB, due to the quenching of both hemin and Au@CeO 2 NPs. As a result, the signal-off aptasensor showed a wider linear range response from 10 −13 to 10 −8 M with lower detection limit of 0.03 pM. [ABSTRACT FROM AUTHOR]

Abstract: In this work, a novel polyamidoamine (PAMAM) dendrimer-l-cysteine-hollow gold nanospheres nanocomposite was fabricated and used as the promoter for the peroxydisulfate/O2 ECL system to detect the concentration of the tumor marker carcinoembryonic antigen (CEA). Herein, the carboxyl-terminated PAMAM dendrimers were decorated with l-cysteine (l-Cys) by EDC/NHS coupling chemistry. Then, the hollow gold nanospheres (HGNPs) were employed as effective nano-carriers for the assembly of PAMAM-l-Cys via thiols-Au bonding, which was used for further loading of detection antibody (Ab2) to form the PAMAM-l-Cys-HGNPs-Ab2 bioconjugates. In the presence of target CEA, the sandwiched immuno-structure can be formed between the capture anti-CEA antibodies (Ab1), which self-assembled on deposited gold modified electrode, and the Ab2 on the PAMAM-l-Cys-HGNPs, thereby resulting in a proportional increase in ECL response, due to the significant enhancement of PAMAM-l-Cys-HGNPs toward peroxydisulfate/O2 ECL system. As a result, a sandwich ECL assay for CEA detection was developed with excellent sensitivity of a large concentration variation from 20fg/mL to 1.0ng/mL and a detection limit of 6.7fgmL−1. [Copyright &y& Elsevier]

Abstract: In this paper, a novel sensitive “signal off” electrochemiluminescence (ECL) immunosensor was constructed by ferrocene functionalized chitosan nanoparticles (Fc-CsNPs) as tag for quenching peroxydisulfate system emission for the first time. Herein, CsNPs were prepared by a facile counterion complex coacervation method, and then numerous Fc and detection antibodies (Ab2) were immobilized together via covalent cross-linking. The sensing platform was constructed by assembling carboxyl polyamidoamine (PAMAM) dendrimers onto bovine serum albumin (BSA) modified electrode. Herein, BSA layer provided a multifunctional interface with good biocompatibility and sufficient active sites to produce conjugates with PAMAM. Then, PAMAM may play dual roles that not only as carriers to immobilize numerous capture antibodies but also as enhancer to significantly increase the ECL of peroxydisulfate system, thus, greatly improving the immunosensors’ sensitivity. After a sandwich-type immunoreaction, a remarkable decrease of ECL signal was observed due to the ECL quenching of peroxydisulfate by Fc-CsNPs labeled Ab2. As a result, the logarithm of change of ECL intensity has a direct relationship with the logarithm of N-terminal pro-B-type natriuretic peptide concentration in the range of 0.001–2pg/mL with a detection limit of 0.33fg/mL (S/N=3). [Copyright &y& Elsevier]

Abstract: An electrochemiluminescent (ECL) aptasensor was fabricated and used for the amplified detection of thrombin (TB) based on DNA supersandwich structure. Herein, hollow gold nanospheres (HGNPs) were firstly employed as effective tag-carriers for the immobilization of detection aptamer (TBA 2) to form the HGNPs labeled TBA 2 (HGNPs-TBA 2). Subsequently, streptavidin (SA) was used to block the non-specific binding sites of HGNPs-TBA 2 as well as to supply binding sites, which could further introduce numerous initiator DNA strands (bio-S1) via biotin–streptavidin specific interaction. Next, bio-S1 could in situ trigger hybridization chain reaction (HCR) to create a long nicked double helices analogous (dsDNA) in the present of ssDNA S2 and ssDNA S3 (S3 is partially complementary to the S2) to obtain the DNA supersandwich structure. Furthermore, Ru(phen)3 2+, a well-known ECL luminophore, could be intercalated into the grooves of dsDNA (Ru-dsDNA) to form the Ru-dsDNA-SA-HGNPs-TBA 2 bioconjugate. As a result, the target of TB was sandwiched between Ru-dsDNA-SA-HGNPs-TBA 2 and TBA 1. In this strategy, numerous Ru(phen)3 2+ could be immobilized on the electrode based on the supersandwich structure, resulting in an increased ECL signal output. A supersandwich ECL assay for TB detection was developed with excellent sensitivity of a large concentration variation from 5fM to 50pM and a detection limit of 1.6fM. [Copyright &y& Elsevier]

Developing low-cost and efficient methods to enhance the electrochemiluminescence (ECL) intensity of luminophores is highly desirable and challenging. Herein, we develop a synergistic promotion strategy based on three types of co-reaction accelerators to achieve an efficient SnO 2 quantum dots (SnO 2 QDs)-based ternary ECL system. Specifically, the MnO 2 nanoflowers (MnO 2 NFs), Ag nanoparticles (Ag NPs) and hemin/G-quadruplex were rationally selected as co-reaction accelerators. Owing to the synergistic effect, the deft integration of three types of co-reaction accelerators enabled better structural stability, more exposed catalytic active sites, and faster charge transfer, thus more effectively facilitating the reduction of co-reactant (S 2 O 8 2−) compared with that of the single co-reaction accelerator. To demonstrate the practical utility of this principle, an "on-off-super on" ECL biosensor was constructed in combination with a 3D DNA walker, which showed a superior linear range (10 aM–100 pM) and a low detection limit (2.9 aM) for the highly-sensitive miRNA-21 detection. In general, this work firstly reported that three types of co-reaction accelerators were deftly integrated to remarkably amplify the ECL emission of SnO 2 QDs, and provided brand-new perspectives for research on the ingenious design of the structure and component of highly efficient co-reaction accelerators. • A synergistic promotion strategy was used to achieve an efficient SnO 2 QDs-based ternary ECL system. • An extraordinarily strong ECL signal of SnO 2 QDs was obtained based on the synergistic effect. • The "on-off-super on" ECL biosensor was successfully constructed for miRNA-21 detection. [ABSTRACT FROM AUTHOR]