Fig. 4. Biomolecular and cellular interactions regulated by plastics–water interfaces.
a, An illustration of accumulation and damage of biomolecules and cells at microplastic surfaces. b, Confocal fluorescence imaging of charged biomolecules, including positively charged proteins such as WGA (left), negatively charged R-PE (middle), and DNA (right), revealed their selective partitioning at the plastic–water interface. Strong accumulation of charged biomolecules is observed on PP microplastics, whereas negligible accumulation is observed at more hydrophilic PMMA or the same PP with 0.1% Triton X-100. c–g, Protein aggregation arising from intrinsic physicochemical activity at plastic–water interfaces. c, An illustration of fluorogenic ThT assay for imaging protein aggregation. d, Thioflavin surface fluorescence (Ft/F0, where F0 and Ft denote the surface fluorescence of the same particle before and after incubation) for lysozyme on PS microplastics with and without caffeine (a radical scavenger). The reference line (Ft/F0 = 1) is indicated by the grey dashed line. Caffeine can completely suppress protein aggregation, as reflected by most data points at or below the reference line. Points indicate fluorescence from individual particles; n = 17 and 23 individual particles for PS and PS with caffeine, respectively. Data are mean ± s.e.m. ****P < 0.0001 (two-sided Wilcoxon rank-sum test). e, Confocal images of ThT binding to protein aggregates from lysozyme at PS–water interfaces in PBS buffer or in the presence of 0.1% Triton X-100 after equal incubation time. f, Time trace of ThT fluorescence intensity at PS–water interfaces, with or without Triton X-100. Data are representative of duplicate experiments. g, ThT fluorescence intensity quantification measured at particle surfaces of different commodity plastics with 0.1 mg ml−1 lysozyme in PBS buffer. Values are presented as area-weighted mean fluorescence intensities ± s.d. from particle regions for PP (n = 10), PE (n = 10), PS (n = 7), PVC (n = 7), PET (n = 6), and PMMA (n = 6), respectively. h–i, Microplastic interactions with cells as demonstrated by haemolytic activity. h, Erythrocytes fragmented into schistocytes upon interaction with PS microplastics as shown by the time-lapse optical micrographs. i, Haemolytic activity quantification for different commodity microplastics by measuring the optical density (OD; absorbance) at 405 nm of haemoglobin released into the supernatant. PBS buffer with no microplastic is utilized as a control. Data are mean ± s.d.; n = 4 independently prepared samples per group, including the PBS control. Scale bars, 50 µm (b,e).