A label-free electrochemical biosensor for trace uranium based on DNAzymes and gold nanoparticles

A novel and highly sensitive electrochemical DNAzymes biosensor was fabricated using Au nanoparticles (AuNPs) immobilized on the surface of Au electrode that had been previously modified with self-assembled monolayers of 1,6-hexanedithiol. Different modified electrodes were prepared and characterized by cyclic voltammetry and electrochemical impedance spectroscopy. The AuNPs were found to have a large surface area to anchor a large number of negatively charged phosphate backbones of DNAzymes, which further absorbed the electroactive indicator of hexaammineruthenium(III) ([Ru(NH 3 ) 6 ] 3+ ) to amplify the electrochemical signal. In the presence of target molecules, a large amount of DNA partly associated with [Ru(NH 3 ) 6 ] 3+ were removed from the electrode surface, leading to a significant decrease in peak current. Differential pulse voltammetry signals of [Ru(NH 3 ) 6 ] 3+ provided quantitative measures of the concentrations of uranyl ion (UO 2 2+ ), with linear calibration ranging from 13 pM to 0.15 nM and a detection limit of 5 pM. The presence of other metal ions did not affect the detection of UO 2 2+ , which indicated the high specificity of UO 2 2+ . Therefore, a new electrochemical DNAzymes sensor was designed with specific DNAzymes and AuNPs as immobilization platform and signal amplifier.