A label-free electrochemical biosensor for detection of uranyl ions in water based on nucleic acid dye-inducing turn-off of photosensitization

A DNAzyme-based photocatalytic electrochemical biosensor was developed for the label-free detection of uranyl   ions (UO 2 2+ ) in water. In this sensing platform, SYBR Green (SG) molecules were embedded in double-stranded DNA (dsDNA), which was cleaved via formed singlet oxygen ( 1 O 2 ) during photosensitization, resulting in a significant decrease in the impedance signal of [Fe (CN) 6 ] 3−/4− . In the presence of UO 2 2+ , the substrate strand was cleaved by the target UO 2 2+ , releasing the SG molecule from the dsDNA, and the photosensitive reaction was turned off. Therefore, UO 2 2+ can be detected based on changes in [Fe(CN) 6 ] 3−/4− electrochemical signals. Such a sensing strategy allowed the detection of UO 2 2+ in the concentration range of 1–1000 nM, with a limit of detection (LOD) of 1.3 × 10 −10 M. The LOD meets the maximum allowable contamination level (1.3 × 10 −7 M) of UO 2 2+ in drinking water set by the US Environmental Protection Agency (EPA). The proposed sensor has been successfully applied for detection of UO 2 2+ in spiked actual water samples with recoveries in the range of 88.0 %–103 %, comparable to those obtained by ICP-MS. The method, which combines photocatalysis with an electrochemical biosensor, significantly improved the sensitivity for UO 2 2+ detection without the need of labeling and additional signal amplification steps. It is also a promising strategy for rapid monitoring of UO 2 2+ in environmental water samples.