Gold nanoparticles superlattices assembly for electrochemical biosensor detection of microRNA-21

•A novel electrochemical biosensor was developed for circulating microRNA-21 detection.•The nanoparticle superlattice was used to amplify the electrochemical signals.•The toluidine blue with higher affinity used as microRNA intercalative label.•A lower detection limit of 78 aM was obtained with good selectivity and repeatability.•The human plasma assay proved its potential for clinical breast cancer detection.

Gold nanoparticles (AuNPs) superlattice and small molecule dyes such as toluidine blue have remarkable effect on signal amplification. In this report, a label-free and simple electrochemical microRNA biosensor is developed by employing toluidine blue (TB) as a redox indicator and AuNPs superlattice as a support material. Conductive polymer, polypyrrole coated AuNPs was self-assembled to form a superlattice which exhibited the most close-packed type thereby producing the maximum current. The successful immobilization of the single strand RNA (ss-RNA) probe and hybridization with the target microRNA sequence were confirmed by electrochemical cyclic voltammetry (CV) methods as well as differential pulse voltammetry (DPV) technique, which was used to determine the oxidation peak current of TB under optimal condition. TB with efficient signal amplification was applied in microRNA biosensor for the first time. By employing this strategy, microRNA can be detected in a range from 100 aM to 1 nM with a relatively low detection limit of 78 aM. Alongside the outstanding sensitivity and selectivity, this nanobiosensor had great reproducibility and showed a remarkable response in the real sample analysis with serum samples. In conclusion, the proposed electrochemical nanobiosensor could be clinically useful in the early detection of the breast cancer by direct detection of the serum microRNA-21 in real clinical samples without sample preparation, RNA extraction and/or amplification.

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