Ultrasensitive microfluidic paper-based electrochemical/visual biosensor based on spherical-like cerium dioxide catalyst for miR-21 detection.

In this work, an electrochemical biosensor based on Au nanorods (NRs) modified microfluidic paper-based analytical devices (μPADs) were constructed for sensitive detection of microRNA (miRNA) by using cerium dioxide - Au@glucose oxidase (CeO2-Au@GOx) as an electrochemical probe for signal amplification. Au NRs were synthesized by in-situ growth method in μPADs surface to enhance the conductivity and modified hairpin probe through Au-S bonds. The construction of "the signal transducer layer" was carried out by GOx catalyzing glucose to produce H2O2, which was further electrocatalyzed by CeO2. After the biosensor was constructed, an obvious electrochemical signal was observed from the reduction of H2O2. In order to make the detection more convincing, the visual detection was performed based on the oxidation of 3,3',5,5'-tetramethylbenzidine by H2O2 with the help of Exonuclease I. The electrochemical biosensor provided a wide linear range of 1.0fM to 1000fM with a relatively low detection limit of 0.434fM by the electrochemical measurement. Linear range of 10fM to 1000fM with a relatively low detection limit of 7.382fM was obtained by visual detection. The results indicated the proposed platform has potential utility for detection of miRNA.