Highly Sensitive Aptasensor for Trace Arsenic(III) Detection Using DNAzyme as the Biocatalytic Amplifier

A highly sensitive fluorescence biosensing system was designed for the detection of trace amounts of arsenic(III) (As³⁺) based on target-triggered successive signal amplification strategy. The specific recognition between the target As³⁺ and the aptamer sequence results in the release of the blocking DNA to trigger the subsequent signal amplification steps. Exonuclease III (Exo III)-mediated DNA recycling digest process is introduced into the sensing system to generate numerous Mg²⁺-dependent DNAzymes. After magnetic separation, the active DNAzyme with multiple turnovers could catalyze the continuous cleavage of the fluorophore-quencher-functionalized substrate strands, thus yielding a significantly amplified fluorescence signal for target detection. Due to the synergetic signal amplification of Exo III and DNAzyme, the fluorescent biosensor exhibits ultrasensitivity for As³⁺ monitoring, with a detection limit of 2 pM. Our established biosensor also displays excellent selectivity toward the target As³⁺ and has been successfully applied to the determination of As³⁺ in water samples with satisfactory accuracy. This sensing platform can be developed as a universal approach for the fast, sensitive, and accurate detection of aptamer-binding molecules.