A Tunable Threshold Colorimetric DNA Logic Gate for Intuitive Assessment of Chemical Contaminant Exceedance

Current molecular logic gates are predominantly focused on the qualitative assessment of target presence, which has certain limitations in scenarios requiring quantitative assessment, such as chemical contaminant monitoring. To bridge this gap, we have developed a novel DNA logic gate featuring a tunable threshold, specifically tailored to the limits of contaminants. At the core of this logic gate is a DNA-gold nanoparticle (AuNP) hybrid film that incorporates aptamer sequences to selectively bind to acetamiprid (ACE) and atrazine (ATR). Upon interaction with these contaminants, the film degrades, releasing AuNPs that, in the presence of Hg²⁺, catalyze the oxidation of TMB, resulting in a visible blue coloration on test paper. This aptamer-enabled process effectively establishes an OR logic gate, with ACE and ATR as inputs and the appearance of blue color as the output. A key innovation of our system is its tunable input threshold. By adjusting the concentration of Hg²⁺, we can fine-tune the color mutation points to match the input threshold to predefined limits, such as Maximum Residue Limits (MRLs). This alignment allows semiquantitative assessment of contaminant levels, providing intuitive visual feedback of contaminant exceedance. Validation experiments with spiked samples confirm its accuracy and reliability by closely matching HPLC results. Therefore, our colorimetric DNA logic gate is emerging as a promising tool for easy and semiquantitative monitoring of chemical contaminants across diverse applications.