Microplastics in the environment produced by decomposition of globally increasing waste plastics have become a dominant component of both water and air pollution. To examine the potential toxicological effects of microplastics on human cells, the cultured human alveolar A549 cells were exposed to polystyrene microplastics (PS-MPs) of 1 and 10 μm diameter as a model of the environmental contaminants. Both sizes caused a significant reduction in cell proliferation but exhibited little cytotoxicity, as measured by the maintenance of cell viabilities determined by trypan blue staining and by Calcein-AM staining. The cell viabilities did not drop below 93% even at concentrations of PS-MPs as high as 100 μg/mL. Despite these high viabilities, further assays revealed a population level decrease in metabolic activity parallel in time with a dramatic decrease in proliferation rate in PS-MP exposed cells. Furthermore, phase contrast imaging of live cells at 72 h revealed major changes in the morphology of cells exposed to microplastics, as well as the uptake of multiple 1 μm PS-MPs into the cells. Confocal fluorescent microscopy at 24 h of exposure confirmed the incorporation of 1 μm PS-MPs. These disturbances at the proliferative and cytoskeletal levels of human cells lead us to propose that airborne polystyrene microplastics may have toxicologic consequences. This is the first report of exposure of human cells to an environmental contaminant resulting in the dual effects of inhibition of cell proliferation and major changes in cell morphology. Our results make clear that human exposure to microplastic pollution has significant consequence and potential for harm to humans.

Stem-cell-derived extracellular vesicles (EVs) are promising tools for therapeutic delivery and imaging in the medical research fields. EVs that arise from endosomal compartments or plasma membrane budding consist of exosomes and microvesicles, which range between 30 and 200 nm and 100–1000 nm, respectively. Iron oxide nanoparticles can be used to label stem cells or possibly EVs for magnetic resonance imaging. This could be a novel way to visualize areas in the body that are affected by neurological disorders such as stroke. Human induced pluripotent stem cells (iPSK3 cells) were plated on low-attachment plates and treated with SB431542 and LDN193189 during the first week for the induction of cortical spheroid formation and grown with fibroblast growth factor 2 and cyclopamine during the second week for the neural progenitor cell (iNPC) differentiation. iNPCs were then grown on attachment plates and treated with iron oxide (Fe3O4) nanoparticles at different sizes (8, 15, and 30 nm in diameter) and concentrations (0.1, 10, and 100 μM). The spheroids and media collected from these cultures were used for iron oxide detection as well as EV isolation and characterizations, respectively. MTT assay demonstrated that the increased size and concentration of the iron oxide nanoparticles had little effect on the metabolic activity of iNPCs. In addition, the Live/Dead assay showed high viability in all the nanoparticle treated groups and the untreated control. The EVs isolated from these culture groups were analyzed and displayed similar or higher EV counts compared with control. The observed EV size averaged 200–250 nm, and electron microscopy revealed the expected exosome morphology for EVs from all groups. RT-PCR analysis of EV biogenesis markers (CD63, CD81, Alix, TSG101, Syntenin1, ADAM10, RAB27b, and Syndecan) showed differential expression between the iron-oxide-treated cultures and nontreated cultures, as well as between adherent and nonadherent 3D cultures. Iron oxide nanoparticles were detected inside the cortical spheroid cells but not EVs by MRI. The addition of iron oxide nanoparticles does not induce significant cytotoxic effects to cortical spheroids. In addition,, nanoparticles may stimulate the biogenesis of EVs when added to cortical spheroids in vitro.

Microplastics have gained much attention due to their prevalence and abundance in our everyday lives. They have been detected in household items such as sugar, salt, honey, seafood, tap water, water bottles, and food items wrapped in plastic. Once ingested, these tiny particles can travel to internal organs such as the kidney and liver and cause adverse effects on the cellular level. Here, human embryonic kidney (HEK 293) cells and human hepatocellular (Hep G2) liver cells were used to examine the potential toxicological effects of 1 μm polystyrene microplastics (PS-MPs). Exposing cells to PS-MPs caused a major reduction in cellular proliferation but no significant decrease in cell viability as determined by the trypan blue assay in both cell lines. Cell viability remained at least 94% for both cell lines even at the highest concentration of 100 μg/mL of PS-MPs. Phase-contrast imaging of both kidney and liver cells exposed to PS-MPs at 72 h showed significant morphological changes and uptake of PS-MP particles. Confocal fluorescent microscopy confirmed the uptake of 1 μm PS-MPs at 72 h for both cell lines. Additionally, flow cytometry experiments verified that more than 70% of cells internalized 1 μm PS-MPs after 48 h of exposure for both kidney and liver cells. Reactive oxygen species (ROS) studies revealed kidney and liver cells exposed to PS-MPs had increased levels of ROS at each concentration and for every time point tested. Furthermore, quantitative reverse transcription polymerase chain reaction (qRT-PCR) analysis at 24 and 72 h revealed that both HEK 293 and Hep G2 cells exposed to PS-MPs lowered the gene expression levels of the glycolytic enzyme, glyceraldehyde-3-phosphate dehydrogenase ( GAPDH ), and antioxidant enzymes superoxide dismutase 2 ( SOD2 ) and catalase ( CAT ), thus reducing the potential of SOD2 and CAT to detoxify ROS. These adverse effects of PS-MPs on human kidney and liver cells suggest that ingesting microplastics may lead to toxicological problems on cell metabolism and cell–cell interactions. Because exposing human kidney and liver cells to microplastics results in morphological, metabolic, proliferative changes and cellular stress, these results indicate the potential undesirable effects of microplastics on human health.

Interactions of plasmonic nanocolloids such as gold nanoparticles and nanorods with proximal dye emitters result in efficient quenching of the dye photoluminescence (PL). This has become a popular strategy for developing analytical biosensors relying on this quenching process for signal transduction. Here, we report on the use of stable PEGylated gold nanoparticles, covalently coupled to dye-labeled peptides, as sensitive optically addressable sensors for determining the catalytic efficiency of the human matrix metalloproteinase-14 (MMP-14), a cancer biomarker. We exploit real-time dye PL recovery triggered by MMP-14 hydrolysis of the AuNP−peptide-dye to extract quantitative analysis of the proteolysis kinetics. Sub-nanomolar limit of detections for MMP-14 has been achieved using our hybrid bioconjugates. In addition, we have used theoretical considerations within a diffusion-collision framework to derive enzyme substrate hydrolysis and inhibition kinetics equations, which allowed us to describe the complexity and irregularity of enzymatic proteolysis of nanosurface-immobilized peptide substrates. Our findings offer a great strategy for the development of highly sensitive and stable biosensors for cancer detection and imaging.

We detail the assembly and characterization of quantum dot (QD)−dye conjugates constructed using a peptide bridge specifically designed to recognize and interact with a breast cancer biomarkermatrix metalloproteinase-14 (MMP-14). The assembled QD conjugates are then used as optically addressable probes, relying on Förster resonance energy transfer (FRET) interactions as a transduction mechanism to detect the activity of MMP-14 in solution phase. The QDs were first coated with dithiolane poly(ethylene glycol) (PEG) bearing a carboxyl group that allows coupling via amide bond formation with different dye-labeled peptides. The analytical capability of the conjugates is enabled by correlating changes in the FRET efficiency with the conjugate valence and/or QD-to-dye separation distance, triggered and modulated by enzymatic proteolysis of surface-tethered peptides. The FRET probe exhibits great sensitivity to enzyme digestion with sub-nanomolar limit of detection. We further analyze the proteolysis data within the framework of the Michaelis–Menten model, which considers the fact that surface-attached peptides have a slower diffusion coefficient than free peptides. This results in reduced collision frequency and lower catalytic efficiency, k cat/K M. Our results suggest that our conjugate design is promising, effective, and potentially useful for in vivo analysis.