An aptamer biosensor for leukemia marker mRNA detection based on polymerase-assisted signal amplification and aggregation of illuminator

A novel electrochemical luminescence (ECL) aptamer biosensor via polymerase amplification is constructed for label-free detection of leukemia marker mRNA (miR-16). In order to achieve the ultrasensitive detection of the target mRNA, the cyclic target chain displacement polymerization of leukemia marker mRNA assisted with Klenow fragment of DNA polymerase is employed. The determination is carried out by recording the ECL emission of pyridine ruthenium (Ru(bpy)(3)(2+)) complexes embedded into the assistance DNA (ADNA) loaded on the nanogold surface, after the hybridization reaction between the probe DNA (PDNA) and the remaining sequence of the CP's stem part, and the formation of a core-shell sun-like structure. The mercapto-modified capture DNA (CP) is immobilized on the surface of a magneto-controlled glassy carbon electrode by Au-S bond. The CP is opened and hybridized with the target mRNA to form double-stranded DNA. In the presence of polymerase, primer DNA, and bases (dNTPs), the primer chain gets access to its complementary sequence of the stem part and then triggers a polymerization of the DNA strand, leading to the release of mRNA and starting the next polymerization cycle. Finally, the composite of PDNA-covered and ADNA-covered (embedded with Ru(bpy)(3)(2+)) gold nanoparticles (hereafter called AuNPs@(PDNA+ADNA-Ru(bpy)(3)(2+)) is added, and the ECL intensity is recorded. Because of the polymerization cycle and the aggregation of the illuminator of Ru(bpy)(3)(2+), the detected signal is amplified significantly. The results showed that the corresponding ECL signal has a good linear relationship with a logarithm of target mRNA concentration in the range of 1x10(-16) to 1x10(-7)mol/L, with a detection limit of 4.3x10(-17)mol/L. The mRNA spiked in the human serum sample is determined, and the recoveries are from 97.2 to 102.0%. This sensor demonstrates good selectivity, stability, and reproducibility.