Combining padlock exponential rolling circle amplification with CoFe 2 O 4 magnetic nanoparticles for microRNA detection by nanoelectrocatalysis without a substrate.

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 CoFe2 O4 magnetic nanoparticles (CoFe2 O4 MNPs) by nanoelectrocatalysis without a substrate for signal amplification. Here, to improve catalytic efficiency, nanocatalyst (CoFe2 O4 MNPs) and redox molecule (Tb) were co-immobilized onto the graphene (Gra) surface and formed Au@CoFe2 O4 /Tb-Gra probe. The obtained probe exhibits high-performance Tb catalysis by reducing the interaction distance between CoFe2 O4 MNPs and Tb, and importantly, the detection sensitivity is significantly improved even in the absence of substrate (H2 O2 ). 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.