DNA-functionalized gold nanoparticle-based fluorescence polarization for the sensitive detection of silver ions.

Despite their practical applications, Ag ions are environmental pollutants and affect human health. So the effective detection methods of Ag ions are imperative. Herein, we developed a simple, sensitive, selective, and cost-effective fluorescence polarization sensor for Ag detection in aqueous solution using thiol-DNA-functionalized gold nanoparticles (AuNPs). In this sensing strategy, Ag ions can specifically interact with a cytosine-cytosine (CC) mismatch in DNA duplexes and form stable metal-mediated cytosine-Ag-cytosine (C-Ag-C) base pairs. The formation of the C-Ag-C complex results in evident changes in the molecular volume and fluorescence polarization signal. To achieve our aims, we prepared two complementary DNA strands containing C-base mismatches (probe A: 5'-SH-A-TACCACTCCTCAC-3' and probe B: 5'-TCCTCACCAGTCCTA-FAM-3'). The stable hybridization between probe A and probe B occurs with the formation of the C-Ag-C complex in the presence of Ag ions, leading to obvious fluorescence quenching in comparison to the system without AuNP enhancement. The assay can be used to identify nanomolar levels of Ag within 6 min at room temperature, and has extremely high specificity for Ag, even in the presence of higher concentrations of interfering metal ions. Furthermore, the sensor was successfully applied to the detection of Ag ions in environmental water samples and showed excellent selectivity and high sensitivity, implying its promising application in the future.