Ultrasensitive electrochemical sensing platform for miRNA-21 detection based on manganese dioxide-gold nanoparticle nanoconjugates coupled with hybridization chain reaction and horseradish peroxidase signal amplification

In this study, an ultrasensitive electrochemical miRNA-21 biosensor is described. Manganese dioxide-gold nanoparticle (MnO2-Au NP) nanoconjugates were employed as sensing base materials, miRNA-21 was selected as a model analyte, and hybridization chain reaction (HCR) was employed to form long DNA concatemers using two different oligonucleotides with a complementary sequence. Thus, lots of biotin were loaded on DNA concatemers and one of them was labelled with biotin at its 3' terminal. The biosensor was designed as follows: a sulfhydryl-hairpin probe (HP) was first dropped on the surface of the glassy carbon electrode (GCE) modified with MnO2-Au NP nanoconjugates (HP/MnO2-AuNPs/GCE). After it was treated with MCH, the modified electrode was hybridized with miRNA-21, resulting in the loop of HP being opened to form a vertical structure. Subsequently, the modified electrode (miRNA-21/HP/MCH/MnO2-AuNPs/GCE) was incubated with DNA concatemers to form a sandwich structure of HP-miRNA-21-DNA concatemers on the modified electrode surface. Finally, the streptavidin-HRP conjugates were linked to the sandwich structure by specific recognition interaction between biotin and avidin. Differential pulse voltammetry (DPV) was used to measure the electrochemical response of the biosensor in the phosphate-buffered solution (0.10 M PBS, pH 7.0) containing 2.0 mM hydroquinone (HQ) and 1.8 mM H2O2. As a result, a larger reductive signal was obtained at a potential of -0.17 V (vs. SCE). Various experimental conditions were optimized, including solution pH, incubation time, and the amount of DNA concatemers. Under optimal conditions, the biosensor showed good sensing performance, such as a wide linear response range (0.1 fM and 100 nM) and low detection limit (0.063 fM, at S/N = 3). Meanwhile, the biosensor can discriminate single base matched miRNA-21, indicating that the biosensor had good selectivity.