Single Molecular Investigation of Influence of Silver Ions on Double-Stranded and Single-Stranded DNA

The effect of metal ions on DNA base pairs is crucial for understanding the molecular mechanisms underlying metal-ion-associated gene mutations and has broad applications across various fields. We investigated the interaction between silver ions (Ag⁺) and DNA using single-molecule magnetic tweezers (MT), atomic force microscopy (AFM), and dynamic light scattering (DLS). Our findings reveal that monovalent Ag⁺ can compact DNA directly even at very low concentrations, unlike canonical monovalent ions such as sodium and potassium, which have no effect. We attribute this to the specific binding of Ag⁺ to DNA. For both double-stranded DNA (ds-DNA) and single-stranded DNA (ss-DNA), the critical condensing force (Fc) induced by Ag⁺ initially increases with cationic concentration, reaches a maximum value, and then decreases. We found that the variation in condensing force is due to the rise and fall of silver ions associated with DNA, which is different from the monotonous increase of associated regular cations such as La³⁺ or CoHex³⁺. Notably, the condensing forces for partially denatured DNA by DMSO (including ss-DNA) are larger than those for ds-DNA under the same conditions.