Visualizing nanoplastic-metal ion co-exposure stress with an NIR biothiol responsive fluorescent probe

Visualizing the combined toxic effects of micro(nano)plastics and heavy metal ions remains challenging due to the lack of suitable in situ imaging tools, and current co-exposure models are often simplified by simple mixing rather than using pre-formed complexes. In this work, a near-infrared biothiol fluorescent probe was developed based on a naphthalimide scaffold with an α,β-unsaturated acetyl group as a recognition site. The probe exhibits high sensitivity and selectivity toward biothiols, and the detection limit was determined to be 0.47 μM for Cys, 0.37 μM for GSH, and 0.95 μM for Hcy, respectively. This enables the monitoring of biothiol fluctuations in living cells and zebrafish. Using pre-formed PMMA-Hg²⁺ complexes as co-exposure pollutant models, we investigated nanoplastic-metal ion complex induced oxidative stress in living cells and zebrafish. Imaging results revealed that PMMA-Hg²⁺ complex co-exposure induces distinct biothiol fluctuation patterns compared to single exposure of PMMA or Hg²⁺. The surface charge alterations of complexes and lysosomal function were found to be involved in the process. This study provides visual evidence for elucidating the combined toxicity mechanisms of nanoplastic-heavy metal complex co-exposure.