Programmable two-dimensional CoOOH nanosheets with a hybridization chain reaction amplification system for label-free fluorescent detection of miRNA-205 in colorectal cancer.

MicroRNA-205 (miRNA-205) has been identified as a promising biomarker, yet its clinical application is hindered by the lack of detection strategies that combine simplicity, ultrahigh sensitivity, and high specificity. To address these obstacles, we introduced an innovative biosensor integrating hybridization chain reaction (HCR) with two-dimensional CoOOH nanosheets for precisely detecting the colorectal cancer biomarker miRNA-205 (HCR-CoOOH system). This system took advantage of the preferential binding of CoOOH nanosheets for single-stranded DNA over double-stranded DNA, along with HCR for signal amplification. Without the target miRNA-205, hairpin probes H1 and H2 were adsorbed onto CoOOH nanosheets, resulting in effective FRET-based quenching of the intercalated SYBR Green I fluorescence. In contrast, introduction of the target triggered the HCR cascade, producing numerous long double-stranded DNA polymers. Low affinity between these duplexes and the nanosheets allowed substantial fluorescence recovery under isothermal conditions. A strong linear relationship was observed between fluorescence recovery and miRNA-205 concentration over 0.1-500 nM, with a detection limit of 0.062 nM. Furthermore, the system demonstrated excellent specificity and robust performance in serum samples. Notably, this work circumvented the issues of tedious handling and strong background interference by enabling a swift switch from the "signal-off" to the "signal-on" detection mode, while also simplifying the workflow and reducing non-specific signals. Furthermore, the use of SYBR Green I eliminated the need for covalent fluorophore labeling, markedly reducing assay cost. This versatile strategy provides a valuable new tool for colorectal cancer research and clinical diagnostics.