An Upconversion Fluorescent Resonant Energy Transfer Biosensor for the Detection of microRNA through DNA Hybridization

MicroRNAs (miRNAs), a class of small molecules with important regulatory functions, have been widely used in biosensing as biomarkers for the early diagnosis of various diseases (such as osteoporosis). Therefore, it is necessary to develop a miRNA detection platform with high sensitivity and specificity. Herein, an upconversion biosensor based on fluorescent resonant energy transfer (FRET) for the detection of miRNAs was developed. Gold nanoparticles (AuNPs, fluorescence acceptors) were conjugated with aptamers, while upconversion nanoparticles (UCNPs, fluorescence donors) were functionalized with the corresponding complementary DNA (cDNA). The upconversion luminescence (UCL) is quenched vis FRET due to the good overlap between UCNP fluorescence emission and AuNP absorption. In the presence of the target miRNA, the aptamers preferentially bind to the miRNA, thereby dissociating the UCNP-cDNA from the AuNP-aptamers, resulting in the recovery of the UCL. The UCL recovery efficiency increased in a miRNA concentration-dependent manner, which supported the principle of miRNA quantification. The UCNP-based FRET biosensor exhibited sensitive detection of miRNA-21 (as a model analyte) with low limit of detection of 5.91 pM. In addition, depending on the near-infrared excitation and a simple complementary binding reaction during the detection process, the designed biosensor not only effectively eliminated the autofluorescence but also reduced the detection time.