On the basis of a novel target-cycling synchronized rolling circle amplification (RCA) as a signal amplification strategy and in situ electrochemical generation of silver nanoclusters (Ag NCs) as signal probes, an ultrasensitive and simple electrochemiluminescence (ECL) biosensor was proposed for microRNA (miRNA) detection. It was worth mentioning that the circular template was subtly designed to consist of a guanine-rich (G-rich) region and a binding region for realizing target-cycling synchronized RCA. In the presence of target miR-21, the binding region hybridized with the primer and the target miR-21 to form a ternary "P" junction structure, and then the RCA was triggered from the 3'-end of the primer. Along with the proceeding of RCA, the target miR-21 was released and participated into another trigger of the RCA. On account of the G-rich region in the circular template, the product DNA of the target-cycling synchronized RCA possessed tandem periodic cytosine-rich (C-rich) sequences, which acted as ligands to further in situ electrochemically generate silver nanoclusters (Ag NCs) as ECL signal probes. As expected, the obtained ECL intensity dependent on the amount of the Ag NCs, which was positively related to the concentration of the target miR-21. The ECL assay for miR-21 detection demonstrated excellent linear response to a concentration variation from 100 aM to 100 pM and limit of detection down to 22 aM.

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 M. This indicates that Cu NCs show potential for applications in ECL bioanalysis as a new type of low-cost and superior luminophore candidates.

A target induced cycling strand displacement amplification (SDA) mediated by phi29 DNA polymerase (phi29) was first investigated and applied in a signal-off electrochemiluminescence (ECL) biosensor for microRNA (miRNA) detection. Herein, the target miRNA triggered the phi29-mediated SDA which could produce amounts of single-stranded DNA (assistant probe) with accurate and comprehensive nucleotide sequence. Then, the assistant probe hybridized with the capture probe and the ferrocene-labeled probe (Fc-probe) to form a ternary "Y" structure for ECL signal quenching by ferrocene. Therefore, the ECL intensity would decrease with increasing concentration of the target miRNA, and the sensitivity of biosensor would be promoted on account of the efficient signal amplification of the target induced cycling reaction. Besides, a self-enhanced Ru(II) ECL system was designed to obtain a stable and strong initial signal to further improve the sensitivity. The ECL assay for miRNA-21 detection is developed with excellent sensitivity of a concentration variation from 10 aM to 1.0 pM and limit of detection down to 3.3 aM.

In this work, a kind of novel nitrogen doped hydrazide conjugated carbon dots (NHCDs) with strong anodic electrochemiluminescence (ECL) at a low excitation potential were synthesized via a one-step solvothermal approach and applied to construct biosensor for rapid cancer cell detection. The nitrogen doping induced a shift of the highest occupied molecular orbital (HOMO) to the upper energy level thus lowered the anodic ECL excitation potential of carbon dots. Especially, comparing to nondoped hydrazide conjugated carbon dots, NHCDs exhibited 2.5-fold high ECL quantum efficiency because the lower potential could reduce notably the side reactions in the ECL process. Using the high-performance NHCDs to functionalize the electrode surface, a brief ECL biosensor was fabricated to detect the cell-secreted hydrogen peroxide, which could rapidly distinguish cancer cells from normal cells. What is more, the prepared NHCDs, as the combination of low excitation potential, strong ECL emission, and good biocompatibility, were expected to be popular luminophors for clinical diagnose of cancer and monitoring the pharmacodynamics of anticancer drugs.

Although Ru(II)-complex-based bulk nanomaterials have received considerable attention in electrochemiluminescent (ECL) assays owing to their strong ECL signals, the ECL efficiency of these nanomaterials was quite low since the bulk nanomaterials brought about a serious inner filter effect and excess inactive emitters. Herein, hollow porous polymeric nanospheres of a self-enhanced ruthenium complex (abbreviated as Ru-HPNSs) were prepared with a polyethylenimine-ruthenium complex precursor to greatly decrease the inner filter effect and minimize inactive emitters, which significantly improved the ECL efficiency. On the basis of the novel Ru-HPNSs as efficient ECL tags and target-catalyzed hairpin hybridization as signal amplification strategy, an ultrasensitive ECL aptasensor was constructed for the detection of mucin 1 (MUC1), which showed excellent linear response to a concentration variation from 1.0 fg/mL to 100 pg/mL with the limit of detection down to 0.31 fg/mL. It is worth mentioning that this work opened a new avenue for developing high-performance ECL nanomaterials as well as ultrasensitive ECL biosensors for clinical and biochemical analysis.