On-Site Visualization Assay for Tumor-Associated miRNAs:\nUsing Ru@TiO<sub>2</sub> as a Peroxidase-like Nanozyme

Accurate\ndiagnosis of highly aggressive and deadly tumors is essential\nfor effective treatment and improved patient outcomes, and microRNAs\n(miRNAs) have emerged as crucial biomarkers for their roles in tumor\ninitiation, progression, and metastasis. Herein, we present an on-site\nvisualization colorimetric assay for tumor-associated miRNAs using\nruthenium nanoparticle decorated titanium dioxide nanoribbon (Ru@TiO<sub>2</sub>) as a peroxidase-like (POD) nanozyme. Remarkably, the Ru@TiO<sub>2</sub> nanozyme can catalyze the oxidation of chromogenic substrates\nthrough its POD-like activity, which is effectively inhibited by pyrophosphate\ngenerated during the rolling circle amplification process, thereby\nenabling miRNA detection through a visible colorimetric readout. This\napproach provides a highly sensitive and specificity assay for miRNAs\nin diluted human serum with a detection limit of 100 pM. It shows\ngreat potential for clinical diagnostics and biological research,\noffering a promising tool for early cancer diagnosis and molecular\ndiagnostics.