Dual-mode optical nanoprobe based on red-emissive carbon dots for sensitive detection of positively charged nanoplastics

The large-scale production and use of plastics have led to the widespread distribution of nanoplastics (NPs) in environmental media and the food chain. Among various NPs, positively charged nanoplastics (pNPs) generated through aging processes exhibit enhanced bioaccumulation in living organisms and significantly increased biotoxicity. To achieve rapid detection of pNPs in food and environmental samples, this study synthesized red-emissive fluorescent carbon dots (CAT-RCDs) using 3,4-diaminobenzenesulfonic acid and catechol as precursors. Based on this, a sensing platform capable of fluorescence/colorimetric dual-mode detection of positively charged polystyrene nanoplastics (pPS-NPs) was constructed. The sensor exhibited a linear response from 1 to 50 mg/L (fluorescence) and 5–60 mg/L (colorimetric), with detection limits of 0.58 and 1.04 mg/L, respectively. Recovery rates of 90.91–104.80 % confirmed its accuracy. This dual-mode strategy allows visual detection and cross-validation of pPS-NPs, providing a rapid screening tool and a foundation for advanced nanoplastic sensing technologies.