Turn-on fluorescent assay based on purification system via magnetic separation for highly sensitive probing of adenosine

In this work, based on purifying the analysis system by magnetic separation, we constructed a turn-on fluorescent assay for highly sensitive detection of possible biomarkers, employing adenosine as the model target analyte. Aptamer labeled-carbon dots (Apt-CDs) was applied as fluorescence probes as well as selective recognition elements, while Fe3O4@polypyrrole (Fe3O4@PPY) was used as fluorescence quenching and magnetic separating materials for system purification. In absence of adenosine, the Apt-CDs were attached to the surface of PPY through π-π stacking and hydrophobic interaction and its fluorescence was quenched by Fe3O4@PPY. In presence of adenosine, the aptamer could specifically bind with adenosine to form a three dimensional Apt-CDs-adenosine complex and detach from PPY, leading to the fluorescence recovery of Apt-CDs. More importantly, with analysis system purification via twice convenient magnetic separations of free CDs and Apt-CDs-adenosine complex respectively, the detection limit could be reduced from 8 nmol L−1 to 0.15 nmol L−1. This concept offers potential application for simple, rapid, cost-effective, and highly sensitive assay of biological samples.