A ratiometric fluorescent biosensing strategy based on a composite nanoplatform and dual signal amplification for exosomal miRNA detection

Ratiometric fluorescent biosensing has exhibited enormous potential in miRNA detection, demonstrating reli-ability, convenience and efficiency. Nonetheless, the sensitive detection of miRNA at a physiological level by a ratiometric fluorescent strategy remains a challenge. In this work, a ratiometric fluorescent biosensing strategy combining a nanoplatform composed of DNA-templated Ag-Au nanoclusters (Ag-Au NCs/P1) and Au nano-particles/g-C3N4 nanosheets (Au NPs/g-C3N4) with catalytic hairpin assembly (CHA) and sequence-induced fluorescence enhancement is proposed for the precise detection of colorectal cancer-associated miR-92a-3p isolated from exosomes. In the absence of miR-92a-3p, Au NPs/g-C3N4 can adsorb Ag-Au NCs/P1 and effectively quench its fluorescence by photo-induced electron transfer. miR-92a-3p can hybridize with Ag-Au NCs/P1 and trigger the subsequent CHA, causing the formed hybrid duplex to leave the surface of Au NPs/g-C3N4 and recover the fluorescence of Ag-Au NCs/P1. Meanwhile, miR-92a-3p is released and able to hybridize with other Ag-Au NCs/P1, resulting in a signal amplification cycle. Moreover, the proximity of guanine and cytosine makes the hybrid duplex emit stronger fluorescence than Ag-Au NCs/P1, further enhancing the signal. The ratiometric fluorescence system composed of the stable blue fluorescence of Au NPs/g-C3N4 and the varying red fluorescence of Ag-Au NCs/P1 indicates the concentration of miR-92a-3p in the sample. This biosensing strategy exhibits a low detection limit of 0.047 pM and excellent selectivity. Furthermore, it can precisely detect miR-92a-3p isolated from clinical exosome samples, demonstrating its high potential in cancer liquid biopsy.

Automated summary

This article presents a ratiometric fluorescent biosensing strategy for the precise detection of colorectal cancer-associated miR-92a-3p. The strategy combines a nanoplatform composed of DNA-templated Ag-Au nanoclusters and Au nanoparticles/g-C3N4 nanosheets with catalytic hairpin assembly and sequence-induced fluorescence enhancement. It demonstrates a low detection limit, excellent selectivity, and the ability to detect miR-92a-3p in clinical exosome samples.