Core-Shell Au@Nanoplastics as a Quantitative Tracer to Investigate the Bioaccumulation of Nanoplastics in Freshwater Ecosystems.

Studies on the adverse effects of nanoplastics (NPs, particle diameter <1000 nm) including physical damage, oxidative stress, impaired cell signaling, altered metabolism, developmental defects, and possible genetic damage have intensified in recent years. However, the analytical detection of NPs is still a bottleneck. To overcome this bottleneck and obtain a reliable and quantitative distribution analysis in complex freshwater ecosystems, an easily applicable NP tracer to simulate their fate and behavior is needed. Here, size- and surface charge-tunable core-shell Au@Nanoplastics (Au@NPs) were synthesized to study the environmental fate of NPs in an artificial freshwater system. The Au core enables the quantitative detection of NPs, while the polystyrene shell exhibits NP properties. The Au@NPs showed excellent resistance to environmental factors (e.g., 1% hydrogen peroxide solution, simulating gastric fluid, acids, and alkalis) and high recovery rates (>80%) from seawater, lake water, sewage, waste sludge, soil, and sediment. Both positively and negatively charged NPs significantly inhibited the growth of duckweed (Lemna minor L.) but had little effect on the growth of cyanobacteria (Microcystis aeruginosa). In addition, the accumulation of positively and negatively charged NPs in cyanobacteria occurred in a concentration-dependent manner, with positively charged NPs more easily taken up by cyanobacteria. In contrast, negatively charged NPs were more readily internalized in duckweed. This study developed a model using a core-shell Au@NP tracer to study the environmental fate and behavior of NPs in various complex environmental systems.

Effects of size and surface charge on the sedimentation of nanoplastics in freshwater.

The environmental issues caused by nanoplastics (NPs) are increasingly noticeable. Environmental behavior study of the NPs could provide vital information for their environmental impact assessment. However, associations between NPs' inherent properties and their sedimentation behaviors were seldom investigated. In this study, six types of PSNPs (polystyrene nanoplastics) with different charges (positive and negative) and particle sizes (20-50 nm, 150-190 nm and 220-250 nm) were synthesized, and their sedimentations under different environmental factors, (e.g., pH value, ionic strength (IS), electrolyte type and natural organic matter) were investigated. Results displayed that both particle size and surface charge would affect the sedimentation of PSNPs. The maximum sedimentation ratio of 26.48% was obtained in positive charged PSNPs with size of 20-50 nm, while the minimum sedimentation ratio of 1.02% was obtained in negative charged PSNPs with size of 220-250 nm at pH 7.6. The pH value shift (range of 5-10) triggered negligible changes of sedimentation ratio, the average particle size and the Zeta potential. Small size PSNPs (20-50 nm) showed higher sensitivity to IS, electrolyte type and HA condition than large size PSNPs. At high IS value ( [Formula: see text]  = 30 mM or ISNaCl = 100 mM), the sedimentation ratios of the PSNPs all increased differently according to their properties, and the sedimentation promoting effect of CaCl2 was more significant on negative charged PSNPs than positive charged PSNPs. When [Formula: see text] increased from 0.9 to 9 mM, the sedimentation ratios of negative charged PSNPs increased by 0.53%-23.49%, while that of positive charged PSNPs increased by less than 10%. Besides, humic acid (HA) addition (1-10 mg/L) would lead to a stable suspension status for PSNPs in water with different degree and perhaps different mechanism due to their charge characteristics. These results showed new light on influence factor studies of NPs' sedimentation and would be helpful for further knowledge of NPs' environmental behaviors.

Integrated Passive Sensing Chip for Highly Sensitive and Reusable Detection of Differential-Charged Nanoplastics Concentration.

In this work, a new type, highly sensitive, and reusable nanoplastics (NPs) microwave detection method is proposed, which can be used to rapidly analyze NPs with different surface charges and sizes. The effective dielectric constant of NPs varies according to the different concentrations, particle sizes, and surface charges of NPs in aqueous solution. The feasibility of the microwave method for differential-charged NPs detection is verified using a complementary split ring resonator sensor manufactured on a cost-effective printed circuit board, which shows a high sensitivity only for positively charged NPs (PS-NH2) detection. To achieve microwave detection of both positively and negatively charged NPs (PS-SO3H), a microscale spiral-coupled resonator sensing chip is manufactured through integrated passive technology, which demonstrates extremely low detection limits and high sensitivity for both PS-NH2 and PS-SO3H, with different concentrations, particle sizes, and charges. In addition, for NPs solution doped with methyl orange, the device can still perform stable measurements, overcoming the inability of traditional NPs molecular element determination and optical detection methods to detect NPs aqueous solution with organic matter doping and color presence. The proposed microwave detection method could also be extended to sensing detection for detecting other hazardous environmental substances.