An enzymatically amplified electrochemical sensor for the sensitive and label-free monitoring of uranyl ions in environmental waters

Abstract

The accurate and sensitive monitoring of uranyl ions (UO22+) in environmental water is critical for uranium pollution management and public health protection. In this work, we developed a novel label-free electrochemical sensing platform that combined a UO22+-specific DNAzyme with exonuclease III (Exo III)-assisted signal amplification. Upon target binding, the DNAzyme was cleaved, which released an enzyme strand. This strand then hybridized with the surface-confined adjunct probe, forming a duplex that specifically activated Exo III. The enzyme then cleaved the adjunct probe, leading to a cyclic amplification process that directly and efficiently modulated the interfacial electrochemical signal amplification. Using [Fe(CN)6]3−/4− as a redox mediator, the amplified response was measured by differential pulse voltammetry (DPV). The proposed sensor exhibited a wide linear detection range from 0.07 to 1.5 nmol/L and achieved a low detection limit of 28.72 pmol/L, which was attributed to the synergistic amplification effect of Exo III. The system also demonstrated excellent selectivity, reproducibility, and stability. Its practical applicability was verified by the analysis of UO22+-spiked water samples from the Xiangjiang River, with satisfactory recovery rates ranging from 92.55% to 103.47%. This work provided a robust, enzyme-enhanced sensing strategy, showing great potential for monitoring trace UO22+ in environmental matrices.