Label-free DNA Y junction for bisphenol A monitoring using exonuclease III-based signal protection strategy.

A label-free DNA Y junction sensing platform for the amplified detection of bisphenol A (BPA) has been constructed by the ingenious combination of toehold-mediated strand displacement and exonuclease III (Exo III)-based signal protection strategy. Three hairpin probes were utilized as the building blocks to fabricate the DNA Y junction with cascaded signal amplification via a series of toehold-mediated strand displacement reactions. Exo III was employed as a protecting agent for the first time to keep the Y-shaped molecular architecture intact, thereby greatly enhancing the fluorescence intensity of DNA intercalator SYBR Green I. The resulting biosensor exhibits ultrasensitivity towards BPA at low concentration (5 fM) without any labeling, modification, immobilization, or washing procedure. Our proposed sensing system also displays remarkable specificity to BPA against other possible interference molecules. Moreover, this DNA junction biosensor is robust and can be applied to the reliable monitoring of spiked BPA in environmental water samples with good recovery and accuracy. With the successful demonstration for BPA detection, the label-free DNA Y junction can be readily expanded to monitor other analytes in a simple, cost-effective, and ultrasensitive way by substituting the target-specific aptamer sequence.