MicroRNAs (miRs) as biomarkers for early cancer diagnostic, were detected through a developed ultrasensitive electrochemical biosensor containing gold Nano-islands (Au-NIs) structures. Different concentrations of miR-21 (from zepto -molar to micro range) in both standard solution and blood serum samples were measured to test the sensitivity of biosensor. A high surface-area-to-volume ratio of nanostructures embellished on the FTO electrodes increases the chance of immobilization of the thiol modified capture probe (anti-miR-21 or cap-21). The Au-nanostructures surface modification and its ability to hybridize successfully and stably anti-miR-21 and miR-21 confirmed by electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV) electrochemical techniques. The results showed that the linear detection range of the biosensor was from 1.0 zM to 200 nM with a limit of detection (LOD) of 0.12 zM which revealed a very high sensitivity. The selectivity of the biosensor was also investigated and confirmed by detecting miR-9 and miR-486. Corresponding results revealed that the biosensor discriminated target miR-21 from non-complementary miR-21 and showed high selectivity and specificity. Our results also revealed that this platform is a promising substrate to quantitative analysis of miR-21 in physiological samples and could be used for biomedical research and point-of-care (POC) diagnosis. Straightforward and robust Au-NIs surface fabricated without surfactant and stabilizer additive, with plenty of anchors for ssDNA immobilization, as well as well-established hybridization and immobilization procedures, plus high electron transfer rate ability in comparison to bare FTO electrodes are among attractive and suitable novelty of this study.
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