Affinity-Modulated Molecular Beacons on MoS₂ Nanosheets for MicroRNA Detection

DNA-functionalized layered two-dimensional transition-metal dichalcogenides have attracted tremendous interest for constructing biosensors in recent years. In this work, we report diblock molecular beacons with poly-cytosine (polyC) tails anchored on molybdenum disulfide (MoS₂) nanosheets as probes for microRNA detection. The polyC block is adsorbed on MoS₂ and the molecular beacon block is available for hybridization to the target; duplex-specific nuclease provides signal amplification by target recycling. By changing the length of polyC, we regulate the density of probes on MoS₂ and inhibit the adsorption of enzyme-cleaved oligonucleotides, thereby leading to higher quenching efficiency. PolyC-mediated molecular beacons on MoS₂ have very low background signal, ultrahigh sensitivity (limit of detection ∼3.4 fM), specificity to detect a single nucleotide mismatch, and selectivity to detect target microRNA from serum samples. This detection platform holds great potential for quantitative analysis of miRNAs in clinical diagnosis and biomedical research.