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 × 10−5–0.01 M, with a detection limit of 5.0 × 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.
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