Nanoplastics (NPs) act as carriers of heavy metals and complicate toxicity to aquatic organisms due to their affinity for heavy metals, while the particular role of NPs in this joint toxicity remains unclear. Using a dual aggregation-induced emission (AIE) bioimaging technique, we quantitative visualized the AIE luminogens incorporated polystyrene NPs (AIENPs) and metallic Ag+ in Chlamydomonas reinhardtii, aiming to elucidate the toxic mechanisms of coexposed NPs and Ag+. AIENPs with 40 nm and 80 nm diameters, namely 40AIENPs and 80AIENPs, were prepared and subjected to UV irradiation to mimic the natural aging processes. The toxicity results indicated that 40AIENPs and 80AIENPs cocultured with Ag+, altering the phytotoxicity of Ag+ in two distinct ways. The phytotoxicity of Ag+ was intensified by coexposure with 40AIENPs but was alleviated by coexposure with 80AIENPs. Bioimaging results indicated that coexposure with aged 40AIENPs resulted in 1.63±0.04 to 1.74±0.10-fold higher internalization of Ag+ compared to individually exposed Ag+ (normalized based on exposed Ag concentration), resulting in more Ag+ localizing at the apical zones and cell surface. Though coexposure to differently aged 80AIENPs resulted in an increase of 1.17±0.09 to 1.35±0.04-fold in the accumulation of Ag+, the efficiency of internalization of Ag+ decreased by 1.01±0.02 to 1.04±0.02-fold, attributing to a larger amount of Ag+ being absorbed on the cell surface. Mechanistic results indicated that when coexposed with differently aged 40AIENPs, there was an increase in the generation of reactive oxygen species and a decrease in the photosynthetic activities of the algal cells. These effects were different from those observed when coexposed with Ag+ in the presence of 80AIENPs. This study differentiates the bioaccumulation, biodistribution, and biological responses of Ag+ when coexposed with NPs, emphasizing the significant influence of NP sizes and aging degrees.

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