Exonuclease III assisted aptasensor for adenosine detection with gold nanoparticle probes

Herein, a gold nanoparticle (GNP)-based colorimetric aptasensor has been developed for detecting adenosine with exonuclease III (Exo III) assisted recycling amplification. In this aptasensor, two kinds of single-stranded oligonucleotide functionalized GNP probes (Oligo 1-GNPs and Oligo 2-GNPs) are firstly hybridized with one complementary single-stranded oligonucleotide (linker) with the motif of adenosine aptamer, resulting in the formation of GNP aggregates (cross-linked GNPs). In the presence of adenosine, the linker would form a double-stranded DNA (dsDNA) with a recessed 3'-terminus due to its structural switching property, which would lead to disassembly of the cross-linked GNPs. However, upon the addition of Exo III, the dsDNA is enzymatically digested from the 3'-hydroxyl termini, liberating the adenosine. The released adenosine can then interact with another linker and a new round of enzymatic digestion is started. Therefore, remarkable signal amplification is achieved because the disassembly of cross-linked GNPs is strongly dependent on the free adenosine in the reaction mixture. The experimental results demonstrate that the Exo III-assisted GNP-based colorimetric aptasensor is more sensitive (ca. 10 times) than that without Exo III amplification. The Exo III-assisted GNP-based colorimetric aptasensor detects adenosine downs to 5.6 nM, with a linear relationship from 10 nM to 1 mM. Moreover, the Exo III-assisted GNP-based colorimetric aptasensor has been successfully applied to detect Jinshuibao capsule (JSBC) containing adenosine in both a buffer solution and a diluted human serum, demonstrating that this assay has great potential to be employed for detecting adenosine in real samples.