Combining padlock exponential rolling circle amplification with CoFe₂O₄ magnetic nanoparticles for microRNA detection...

In this report, an ultrasensitive electrochemical biosensor for miR-21 detection was designed on the basis of a padlock exponential rolling circle amplification (P-ERCA) assay and CoFe₂O₄ magnetic nanoparticles (CoFe₂O₄ MNPs) by nanoelectrocatalysis without a substrate for signal amplification. Here, to improve catalytic efficiency, nanocatalyst (CoFe₂O₄ MNPs) and redox molecule (Tb) were co-immobilized onto the graphene (Gra) surface and formed Au@CoFe₂O₄/Tb-Gra probe. The obtained probe exhibits high-performance Tb catalysis by reducing the interaction distance between CoFe₂O₄ MNPs and Tb, and importantly, the detection sensitivity is significantly improved even in the absence of substrate (H₂O₂). Simultaneously, to further improve the sensitivity and specificity of the biosensor, P-ERCA assay was introduced. After multiple polymerization and nicking reactions, plenty of P-ERCA amplification product was produced and circular exponential signal amplification was achieved, giving an extreme sensitivity for miR-21 assay. The as-prepared biosensor shows a wide dynamic range of 1 fM to 2 nM with a low detection limit of 0.3 fM for miR-21 detection and exhibits high specificity and sensitivity.