Generally, electrochemiluminescence (ECL) assays are performed in the presence of a coreactant. The addition of the coreactant in the detection solution would make the ECL system lack sufficient stability. In the case of dissolved oxygen as the coreactant, the unknown concentration of dissolved O 2 would result in an inevitable error and a lack of reproducibility in detection. A coreactant-free ECL assay could overcome the above shortcomings and thus is an ideal choice. In this work, a coreactant-free dual amplified ECL strategy was constructed for ultrasensitive detection of microRNA (miRNA). Here, target-catalyzed hairpin assembly and enzyme-triggered DNA walker recycling amplification were integrated to achieve dual signal amplification. Carboxyl-functionalized poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(1,4-benzo-{2,1′-3}-thiadiazole)] (PFBT-COOH) dots were used as luminophores, which displayed prominent ECL performance without adding any coreactants and removing the dissolved O 2 . As a result, the detection of miRNA was achieved, and the linear range was from 10 aM to 5 pM, and the detection limit was low to 3.3 aM. Meanwhile, the practicability of our biosensor was investigated by analyzing the expression of miRNA in cell lysates. The PFBT-COOH dots provided a great platform for constructing coreactant-free ECL biosensors and expanded the application of conjugated polymer dots in clinical analysis.

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Breast cancer has a high fatality rate. Early diagnosis reduces the rate of mortality; therefore, novel diagnostic methods are urgently required. The present study investigated the correlation of serum microRNA (miRNA/miR) expression with breast cancer, and tested a panel of miRNAs as promising potential biomarkers for breast cancer. Six miRNAs (miR‑374, miR‑666‑5p, miR‑451, miR‑148a, miR‑27a and miR‑30b) were selected for analysis and their differential expression levels were quantified using qPCR. The results demonstrated that four out of the six candidate miRNAs were significantly downregulated in breast cancer patients (miR‑451, P=0.000; miR‑148a, P=0.021; miR‑27a, P=0.013 and miR‑30b, P=0.001). A panel of miRNAs consisting of the four downregulated miRNAs was able to distinguish breast cancer from healthy controls, with an area under the receiver operating characteristic curve of 95.3%, a sensitivity of 94.7% and a specificity of 82.8%. Thus, this panel of miRNAs may be used as a sensitive and specific tool for the diagnosis of breast cancer.

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An ultrasensitive electrochemiluminescence (ECL) detection for Cu was explored using the carboxyl functionalized poly(9,9-dioctylfluorenyl-2,7-diyl) (PS-COOH-co-PFO) dots as the signal label without adding any coreactant.