Dual-signal portable microRNA biosensor based on a photothermal/visual strategy induced by cascading amplification techniques and horseradish peroxidase

MicroRNAs (miRNAs) serve as potential biomarkers for many diseases such as cancer, neurodegenerative diseases and cardiovascular conditions. The portable and accurate detection of miRNA is of great significance for the early diagnosis, treatment optimization and prognostic evaluation of diseases. Herein, a photothermal/visual dual-mode assay for let-7a is developed utilizing oxidized 3, 3', 5, 5' - tetramethylbenzidine (oxTMB) as signal reporter. Let-7a efficiently initiates two cascade amplification processes of catalytic hairpin assembly (CHA) and hybridization chain reaction (HCR) on the magnetic microspheres. It is worth noting that the hairpin DNA employed for HCR is labeled with horseradish peroxidase (HRP). Consequently, a substantial accumulation of HRP occurs on the magnetic microspheres and further catalyzes the oxidation of TMB by H₂O₂ to oxTMB. The blue color of oxTMB enables its detection through visual sensing, while the photothermal conversion characteristic of oxTMB allows for its detection through photothermal sensing. The concentration of miRNA is positively correlated with the enrichment of HRP on magnetic microspheres, which in turn affects the production of oxTMB. Therefore, the photothermal and visual dual-mode assay for let-7a can be indirectly realized by the detection of oxTMB. The dual signals are cross-validated to effectively reduce false positives. Precise miRNA quantification is achieved using a household thermometer, which is conducive to the popularization of this proposed strategy. Moreover, by adjusting the hairpin DNA sequences utilized for CHA and HCR, the dual-mode assay platform has a potential to serve as a universal approach for other biomarkers.