Ratiometric near-infrared biosensors based on self-assembled nanoparticles and target-triggered signal amplification...

The abnormal expression of microRNA-21 (miRNA-21) is highly correlated with acute myocardial infarction and can serve as a biomarker for its early diagnosis. In this study, a ratiometric fluorescent probe based on target-triggered signal amplification using upconversion nanoparticles (UCNPs) as energy donors and gold nanoparticles (AuNPs) as energy acceptors was fabricated for the detection of miRNA-21. First, hairpin DNA (H1) with sulfhydryl and amino groups at both terminations is connected to AuNPs and UCNPs through Au-S bonds and amide bonds, leading to the quenching of upconversion luminescence (UCL). The target miRNA-21 can trigger H1 and obtain a miRNA/H1 duplex structure, leading to AuNPs being far from the UCNPs and recovering the UCL. The opened H1 hairpin exposes fragments that can recognize another hairpin DNA (H2) labelled with Cy5, resulting in the target miRNA-21 being replaced by H2 and triggering catalytic hairpin assembly (CHA) signal magnification. The stationary fluorescence of Cy5 and the changing UCL of the UCNPs construct a ratiometric biosensor, which was used to detect miRNA-21, with a low detection limit (LOD) of 0.28 pM. Additionally, this biosensor can determine miRNA-21 in serum samples, with recoveries ranging from 94.3-102.7%, suggesting that the proposed method shows broad prospects in the sensitive and accurate detection of clinical sample biomarkers.