A highly sensitive biosensing platform based on upconversion nanoparticles and graphene quantum dots for the detection of Ag<sup/>.

A novel luminescence 'Turn-On' nanoplatform for the sensitive sensing of Ag was fabricated based on luminescence resonance energy transfer technique between sodium citrate functionalized upconversion nanoparticles (Cit-UCNPs, energy donor) and graphene quantum dots (GQDs, energy acceptor). Amino-labeled single-stranded DNA (NH-ssDNA) containing a number of cytosine (C) was conjugated on the surface of the Cit-UCNPs to capture Ag ions. Due to the π-π stacking interaction between NH-ssDNA and GQDs, the upconversion luminescence can be quenched. However, upon the addition of Ag, the π-π stacking interaction weakens due to the formation of the hairpin structure of C-Ag-C on the UCNPs. As a result, GQDs will leave the surface of the UCNPs and the upconversion luminescence can be enhanced (Turn-On). Based on this fact, the sensor was developed for the detection of Ag with a linear concentration range from 2 × 10 to 1 μM and a detection limit as low as 60 pM. The assay method is fairly simple with high selectivity and sensitivity, which can be used for the determination of Ag in environmental water samples.