Novel multiple strand displacement reaction coupled hybridization chain reaction for label-free and ultrasensitive electrochemical Type b3a2 biosensing.

• A label-free and ultrasensitive DNA biosensor was constructed. • A novel simple multiple strand displacement reaction (MSDR) strategy was employed. • The MSDR was coupled with hybridization chain reaction for signal amplification. • The constructed biosensor achieved a low detection limit of 0.56 fM for Type b3a2 detection. Herein, a novel simple multiple strand displacement reaction (MSDR) coupled hybridization strand reaction (HCR) was proposed for label-free and ultrasensitive Type b3a2 assay. First, two kinds of messenger DNAs (mDNAs) were aligned on a long substrate strand DNA, which was immobilized on magnetic beads. Unlike traditional SDR, in the presence of target and a hairpin DNA, MSDR would be initiated and achieve target-recycling as well as the release of two mDNAs. Finally, one target input can convert into multiple mDNAs, which greatly increased the utility ratio of target. After magnetic separation, the released mDNAs can hybridize with the hairpin DNA immobilized on the electrode to trigger HCR and form a linear duplex-DNA structure. It can be used as an excellent template to in-situ grown silver nanoparticles (AgNPs) to generate electrochemical response directly. By taking advantage of MSDR as well as HCR, the electrochemical signal was amplified significantly. Under optimal conditions, this developed biosensor achieved a low detection limit of 0.56 fM (S/N = 3) and a wide linear range from 10 fM to 10 nM for sensitive detection of Type b3a2 with good selectivity and stability. [ABSTRACT FROM AUTHOR]