A signal-on electrochemical biosensor for sensitive detection of silver ion based on alkanethiol-carbon nanotube-oligonucleotide modified electrodes

A simple, signal-on electrochemical biosensor for sensitive detection of Ag+ was developed based on the three components of alkanethiol, single-walled carbon nanotube (SWNT) and silver ion-specific oligonucleotide (SSO) layer-by-layer modified electrode where square wave voltammetry (SWV) response of K-3[Fe(CN)(6)] at the modified electrode was used for signal transduction. A gold electrode was first assembled with 1-dodecanethiol (C12H25SH) monolayer to which SWNTs were attached. The SWNT surfaces were further noncovalently bound with SSO probes to obtain the sensor interface. The negatively charged SSO probe acts as a physical obstacle and electrostatic repulsion barrier to block the SWNT-mediated long-distance electron transfer of K-3[Fe(CN)(6)] across the -SC12H25 monolayer. Upon Ag+ binding, the SWNT surface-bound SSO probe forms an unimolecular duplex through C-Ag+-C interaction-mediated intramolecular hybridization and departs from the SWNT surface, resulting in decreased electron transfer resistance and increased SWV current of K-3[Fe(CN)(6)] at the modified electrode. This current enhancement effect provides a signal-on mechanism for sensitive transduction of Ag+ recognition and the resulted current increase is linear with the logarithmic concentration of Ag+ from 2.0 nM to 100 nM. The developed biosensor was highly selective and its practical applicability in tap water was also tested with a satisfactory result. (C) 2014 Elsevier B.V. All rights reserved.