An enzyme-free fluorescence biosensor for UO22+ detection using a four-leaf clover-shaped quadruple walker as a signal amplifier.

Given the potential threat of uranium contamination to ecosystems and human health, there is a pressing need to assess UO22+ uptake by Macleaya cordata (M. cordata) in uranium mine environments. To this end, an enzyme-free fluorescence biosensor was designed for ultrasensitive detection of UO22+ employing a DNAzyme as the recognition element and four-leaf clover-shaped quadruple walking as the amplification strategy. In the presence of UO22+, the four-leaf clover-shaped walker could be activated and move autonomously along pre-assembled tracks on MBs through DNAzyme-induced cleavage. As a result, the Cyanine 5 (Cys)/Black Hole Quencher-2 (BHQ2)-labelled tracks were cleaved and a high fluorescence signal was obtained for UO22+ detection. Benefiting from magnetic separation and the high amplification efficiency of four-leaf clover-shaped quadruple walking, the MB platform demonstrated high sensitivity and specificity for UO22+ detection, with a detection limit of 1.9 pM. This sensing system was robust and accurate, achieving the monitoring of trace UO22+ levels in M. cordata. Owing to its unique advantages of enzyme-free format, high sensitivity, excellent selectivity, and fluorescence readout, this sensing system holds great promise for the ultrasensitive sensing of UO22+ in real samples.