Nucleic acid-modulated silver nanoparticles: A new electrochemical platform for sensing chloride ion

Inorganic nanomaterials have generated considerable interest in connection to the design of biosensors. Here we exploit the DNA-induced generation of silver nanoparticles for developing an electrical biosensing protocol for chloride ions. Conjugated with thiol modified oligonucleotide, silver nanoparticles were template-synthesized and immobilized on gold electrode. During cyclic voltammogram (CV) scans, the silver nanoparticles were oxidized at high potential to form a layer of Ag/AgCl complex in the presence of Cl-, giving off sharp solid state redox signals. Under the optimum condition, the electrode responded to Cl- over a dynamic range of 2.0 x 10(-5)-0.01 M, with a detection limit of 5.0 x 10(-6) M. Moreover, the specific solubility product constant-based anion recognition made the electrode applicable at a wide pH range and in complex biological systems. To demonstrate the analytical applications of this sensor in real samples, the Cl- concentrations in human urine were measured without any sample pretreatment. Urinary Cl- detected by the proposed sensor ranged from 110 to 200 mM, which was comparable to the results obtained by standard silver titration.