DNA-Encoded Pd/CeO2 Nanozymes for Colorimetric Sensing of Silver Ions

Abstract Silver ions (Ag+) pose significant ecological and health risks due to their toxicity and potential for bioaccumulation. While conventional detection methods such as ICP-MS and AAS offer high sensitivity, they are often hindered by complex operations, high costs, and limited suitability for on-site analysis. To address this, we developed a highly active and selective colorimetric sensor for Ag+ based on a DNA-encoded Pd/DNA/CeO2 nanozyme. Cerium oxide nanorods (CeO2) serve as an effective support for the directional immobilization of single-stranded DNA through phosphate-Ce4+ coordination and electrostatic interactions. The DNA template guides the uniform in situ growth of palladium nanoparticles (Pd NPs), forming a well-dispersed and highly exposed catalytic interface. The resulting Pd/DNA/CeO2 nanozyme exhibits enhanced peroxidase-like activity, catalyzing the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) in the presence of H2O2. Ag+ ions are specifically reduced on the Pd surface to form a metallic Ag layer, which effectively blocks the active sites and quenches the catalytic activity, enabling a “switch-off” detection mode. The optimized sensor shows a wide linear response to Ag+ from 50 to 400 nM with a detection limit of 22.7 nM. It also demonstrates excellent selectivity against common interfering ions and good applicability in real water samples. This DNA-encoded nanozyme design provides a robust and facile platform for the on-site monitoring of trace Ag+ in environmental systems.