Polydopamine-encapsulated carbon dots to boost analytical performance for microplastics detection in fluorescence mode

A kind of sulfur-doped carbon dots was prepared which were encapsulated with polydopamine (S-CDs@PDA) that has fluorescence response on polyethylene (PE) microplastics (MPs). Modified membranes were constructed using S-CDs@PDA for MP detection. Through heating and vacuum filtration process, yellow emission from the modified membrane appeared because of the combination between S-CDs@PDA and PE MPs. Notably, the fluorescence signal value of PE MPs detected by S-CDs@PDA-modified membrane was 21.3% higher than that of unmodified S-CDs membrane, and the detection efficiency was 8% higher than that of S-CDs membrane. The minimum detection limit for modified membranes was 4 mg. Due to the good adhesion of polydopamine (PDA), S-CDs@PDA-modified membrane was more easily adhered to PE MPs, showing its excellent detection ability. The rapid quantitative detection of PE MPs in 10 min was realized with a linear equation of y = 3081x + 3686.1 in a linear range of 4-14 mg. Such modified membrane exhibited excellent anti-photobleaching using continuous 365-nm excitation and its sensing performance was further confirmed in sea and river water samples. S-CDs@PDA could detect solid MP powders as well as MPs dispersed in liquids. The detection method constructed with a modified glass fiber filter membrane enables rapid identification and quantitative detection of PE MPs without relying on large-scale instrumentation. This study provided research ideas for fluorescent tracing of PE MPs and paved the way for quantitative detection of micron-sized plastics with smaller particle sizes.