Target-responsive DNAzyme hydrogel reinforced by click reaction for surface enhanced Raman scattering detection of okadaic acid

Shellfish toxins are common marine toxins that have attracted worldwide attention due to their serious threats to food safety and human health. In this work, DNA hydrogel based on rolling circle amplification (RCA) and click reaction was developed for surface enhanced Raman scattering (SERS) detection of okadaic acid (OA) combined with target-responsive DNAzyme signal amplification. The RCA strands containing azido-dCTP were combined with cross-linked strands with ethynyl groups via click reaction to form a DNA hydrogel framework. The click reaction strengthened the DNA hydrogel network, making it more rigid and easier to manipulate during the detection process. The aptamer and DNAzyme were introduced into the DNA hydrogel as functionalized DNA components. Upon the specific recognition of OA by the aptamer, the DNAzyme released via the displacement reaction would continuously cleave the enzyme cutting site within the substrate strand to liberate the SERS signal tag. The functionalized DNA hydrogel concurrently achieved the functions of target recognition, signal conversion and signal amplification. Under optimal conditions, this strategy could detect OA with limits of detection as low as 0.2 nmol/L within 30 min. The SERS signal intensity showed good linear relationship with OA concentration in the range of 1.0–300.0 nmol/L. The practical application was validated for detecting trace amounts of OA in aquatic product samples. The stable DNA hydrogel combined with target-responsive DNAzyme signal amplification offers a universal strategy for rapid detection of trace toxins in complex matrixes.