A poly(n-butyl acrylate)-gold-MXene quantum dots (PBA-Au-MXene QD) nanocomposite-based biosensor is presented that is modified by unique antisense single-stranded DNA (ssDNA) and uses the electrochemical detection methods of DPV, CV, and EIS to early detect miR-122 as a breast cancer biomarker in real clinical samples. This fabrication method is based on advanced nanotechnology, at which a poly(n-butyl acrylate) (PBA) as a non-conductive polymer transforms into a conductive composite by incorporating Au-MXene QD. This biosensor had a limit of detection (LOD) of 0.8 zM and a linear range from 0.001 aM to 1000 nM, making it capable of detecting the low concentrations of miR-122 in patient samples. Moreover, it allows approximately 100% sensitivity and 100% specificity for miR-122 without extraction. The synthesis and detection characteristics were evaluated by different complementary tests such as AFM, FTIR, TEM, and FESEM. This new biosensor can have a high potential in clinical applications to detect breast cancer early and hence improve patient outcomes.

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