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In this paper, we describe a novel label-free fluorescence method for microRNA-21 (miR-21) detection based on terbium (Tb3+) and duplex-specific nuclease (DSN) assisted target recycling. Capture probes (Cps), containing a target-binding part and a signal-output part, are immobilized on magnetic beads (MBs). In the presence of the target miR-21, it hybridizes with the target-binding part of a Cp to form a DNA–RNA heteroduplex. Due to the considerable cleavage preference for DNA in DNA–RNA hybrids, DSN hydrolyzes the target-binding part of the Cp while liberating the intact target miR-21 to hybridize with a new Cp and initiate the second cycle of hydrolysis. Eventually, through magnetic separation, only the signal-output part of the Cp could remain in solution and function as a signalling flare to increase the fluorescence intensity of Tb3+ dramatically. By employing the above strategy, this approach can gain an amplified fluorescent signal and detect as low as 8 fM miR-21 under the optimized conditions. Moreover, due to the high selectivity of DSN, the method shows little cross-hybridization among the closely related miRNA family members even at the single-base-mismatched level. Successful attempts were made in applying the approach to detect miR-21 in human cell lysate samples of breast cancer patients. [ABSTRACT FROM AUTHOR]

Locked nucleic acid (LNA) is applied in toehold-mediated strand displacement reaction (TMSDR) to develop a junction-probe electrochemiluminescence (ECL) biosensor for single-nucleotide polymorphism (SNP) detection in the BRCA1 gene related to breast cancer. More than 65-fold signal difference can be observed with perfectly matched target sequence to single-base mismatched sequence under the same conditions, indicating good selectivity of the ECL biosensor. [ABSTRACT FROM AUTHOR]