Enrichment and fluorescence enhancement of adenosine using aptamer–gold nanoparticles, PDGF aptamer, and Oligreen

In this study, we have developed a simple, cost-effective, label-free fluorescence analytical assay – comprising an adenosine-binding aptamer (AptAdo), platelet-derived growth factor (PDGF)-binding aptamer (AptPDGF), gold nanoparticles (Au NPs), and the DNA-binding dye Oligreen (OG) – for the determination of adenosine. AptAdo and AptPDGF are for the recognition of adenosine and for the amplification of fluorescence signal, respectively. The presence of adenosine induces the conformational switch of the AptAdo from coiled to a G-quadruplex structure, leading to the less binding of AptAdo onto the surface of Au NPs. The more the adenosine is present, the less the amount of AptAdo is adsorbed, resulting in the fluorescence change of the aptamer–OG complexes. When using a mixture of AptAdo (15.0 nM), Au NPs (0.1 nM), and OG (0.05×) in 5.0 mM phosphate (pH 7.4), this sensor provides the limit of detection of 70.0 nM for adenosine at a signal-to-noise ratio of 3. The LOD for adenosine is down to 5.5 nM when using AptAdo modified Au NPs (AptAdo–Au NPs) and AptPDGF for the enrichment of adenosine and amplification of fluorescence signal of OG, respectively. The practicality of the present sensor has been validated by the determination of adenosine in diluted urine samples, showing its advantages of simplicity, selectivity, sensitivity, and minimal matrix interference.