A rapid microfluidic paper-based chip sensor using ratiometric fluorescence and molecularly imprinted polymers for visual detection of sulfadiazine in actual samples

In recent years, the widespread use of sulfonamide antibiotics has led to increasing concerns over antibiotic residues. To address the challenges, this study developed a rapid and highly sensitive detection method based on ratiometric fluorescence. By employing nitrogen-doped carbon quantum dots (N-BCDs) and biomass-derived carbon quantum dots (RCDs), single-channel and ratiometric fluorescence sensors were constructed. The incorporation of molecularly imprinted polymers (MIPs) enhanced the specificity and sensitivity of target recognition. Experimental results demonstrated that the ratiometric fluorescence sensor exhibited superior anti-interference capability and detection stability compared to the single-channel sensor, achieving a detection limit as low as 10.41 nM, significantly outperforming the single-channel sensor's limit of 25.94 nM. To enable rapid on-site detection, the ratiometric fluorescence sensor was integrated with a microfluidic paper-based chip, resulting in a visual detection platform. Moreover, a microfluidic paper-based chip with a spatially rotational structure was developed, integrating smartphone photo-recognition functionality to convert fluorescence ratio changes into RGB values, enabling rapid visual detection of SDZ. In practical applications involving milk and water samples, the sensor achieved recovery rates between 98.70 % and 108.70 %, demonstrating excellent performance. This ratiometric fluorescence microfluidic paper-based chip sensor offers simplicity, high sensitivity, and strong selectivity, making it suitable for non-professional users to perform rapid on-site detection. It shows great potential for applications in food safety and environmental monitoring.