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-A₁₀-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.