Sensitive detection of microRNAs using polyadenine-mediated fluorescent spherical nucleic acids and a microfluidic electrokinetic signal amplification chip

The identification of tumor-related microRNAs(miRNAs)exhibits excellent promise for the early diagnosis of cancer and other bioanalytical applications.Therefore,we developed a sensitive and efficient biosensor using polyadenine(polyA)-mediated fluorescent spherical nucleic acid(FSNA)for miRNA analysis based on strand displacement reactions on gold nanoparticle(AuNP)surfaces and electrokinetic signal amplification(ESA)on a microfluidic chip.In this FSNA,polyA-DNA biosensor was anchored on AuNP surfaces via intrinsic affinity between adenine and Au.The upright conformational polyA-DNA recognition block hybridized with 6-carboxyfluorescein-labeled reporter-DNA,resulting in fluorescence quenching of FSNA probes induced by AuNP-based resonance energy transfer.Reporter DNA was replaced in the presence of target miRNA,leading to the recovery of reporter-DNA fluorescence.Subsequently,reporter-DNAs were accumulated and detected in the front of with Nafion membrane in the microchannel by ESA.Our method showed high selectivity and sensitivity with a limit of detection of 1.3 pM.This method could also be used to detect miRNA-21 in human serum and urine samples,with recoveries of 104.0%-113.3% and 104.9%-108.0%,respectively.Furthermore,we constructed a chip with three parallel channels for the simultaneous detection of multiple tumor-related miRNAs(miRNA-21,miRNA-141,and miRNA-375),which increased the detection efficiency.Our universal method can be applied to other DNA/RNA analyses by altering recognition sequences.