Dye displacement-based colorimetric aptasensor for rapid pesticide detection.

Pesticide poisoning incidents occur frequently due to the high toxicity and widespread availability of these chemicals. Achieving rapid and accurate on-site identification of pesticides in complex matrices, independent of bulky laboratory instrumentation, remains a major technical challenge. Therefore, we developed an absorption spectroscopic sensor exploiting the aggregation and disaggregation behaviors of cyanine dyes in solution. Molecular docking was employed to identify the aptamer binding sites and predict affinities. Upon incubation with the specific aptamer, ICG-COOH monomers form a complex with the aptamer via non-covalent interactions, including hydrophobic effects and π-π stacking. The addition of target pesticides induces the formation of a tighter aptamer-target complex. This interaction displaces ICG-COOH into the solution, where the dye aggregates into dimers and generates a distinct change in the absorption signal. The sensor exhibited a linear response to malathion concentrations across two ranges (1-10 μmol/L and 10-30 μmol/L), yielding a limit of detection (LOD) of 0.75 μmol/L. For acetamiprid, a linear relationship was observed from 1 to 5 μmol/L with an LOD of 0.33 μmol/L, alongside a logarithmic fit for higher concentrations ranging from 1 to 50 μmol/L. Applying this same mechanism, a Cy5.5-COOH/aptamer system was designed for atrazine detection. The response followed a logarithmic curve from 1 to 100 μmol/L. A visible color transition from cyan to light blue occurred within this detection range, providing a naked-eye semi-quantitative limit of 10 μmol/L. The successful development of these sensors demonstrates the broad applicability and practical potential of the dye-displacement strategy.