[G3T]5/Tb(3+) based DNA biosensor with target DNA-triggered autocatalytic multi-cycle-amplification and magnetic...

Due to terbium's unique photophysical properties, nucleic-acid-sensitized terbium (DNA/Tb(3+)) bioluminescent system becomes a potential candidate for the fabrication of DNA biosensors. However, the low sensitivity of DNA/Tb(3+) bioluminescent system limits its development. In this paper, a strategy combining autocatalytic multi-cycle-amplification (including exonuclease III (exo III)-aided and Zn(2+)-requiring DNAzyme-assisted target recycling amplifications) and magnetic nanoparticles assisted-background-lowering to improve the sensitivity of DNA/Tb(3+) bioluminescent system is presented for sensitive detection of target DNA (tDNA). The DNA/Tb(3+) bioluminescent system was investigated by ultraviolet-visible (UV-vis) absorption and luminescence spectra. The possible conjugation mechanism and mode of DNA with Tb(3+) were discussed. The autocatalytic multi-cycle-amplification effect was investigated by the comparison of the luminescence. The carboxylation-functionalized Fe3O4-magnetic nanoparticles (MNPs) were characterized and its role in background lowering was proved. As a result, with the designed protocol, the detection limit for the tDNA detection reached a low level to aM, which is especially exciting for the DNA/Tb(3+) bioluminescent system. In the process, due to the separation effect of MNPs, the assay solution was purified to avoid the nonspecific luminescence of DNA/Tb(3+), not only lowering the background signal greatly (about five times lower than that without the use of MNPs but also improving the reproducibility and stability. We hope that our attempt in this field will not only extend the application of DNA/Tb(3+) luminescent system in biosensing areas but also open the road to adaptation of the protocols to other related analytes.