Dimethoate contaminants in food pose a threat to human health. Rapid and sensitive trace detection methods are required to keep food safe. In this study, a novel fluorescent aptasensor was developed for the sensitive detection of dimethoate based on carbon quantum dots labeled with double-stranded DNA (CQDs−apt−cDNA) and Ti₃C₂T_x flakes. Under optimal conditions, the aptasensor showed a good linear range of 1 × 10⁻⁹ to 5 × 10⁻⁵ M for dimethoate with a coefficient of determination (R²) of 0.996. Besides, a low detection limit of 2.18 × 10⁻¹⁰ M was obtained. The aptasensor showed high selectivity in interference samples and good reproducibility with an RSD of 3.06% (<5%) for dimethoate detection. Furthermore, the proposed aptasensor was applied to the detection of dimethoate in apple juice and tap water with satisfactory recoveries from 96.2 to 104.4%. Because of these benefits, this aptasensor has the potential and promise for detecting food contaminants in the food industry.